RNA Sensing by Gut Piezo1 Is Essential for Systemic Serotonin Synthesis.

Gastrointestinal enterochromaffin cells regulate bone and gut homeostasis via serotonin (5-hydroxytryptamine [5-HT]) production. A recent report suggested that gut microbes regulate 5-HT levels; however, the precise underlying molecular mechanisms are unexplored. Here, we reveal that the cation channel Piezo1 in the gut acts as a sensor of single-stranded RNA (ssRNA) governing 5-HT production. Intestinal epithelium-specific deletion of mouse Piezo1 profoundly disturbed gut peristalsis, impeded experimental colitis, and suppressed serum 5-HT levels. Because of systemic 5-HT deficiency, conditional knockout of Piezo1 increased bone formation. Notably, fecal ssRNA was identified as a natural Piezo1 ligand, and ssRNA-stimulated 5-HT synthesis from the gut was evoked in a MyD88/TRIF-independent manner. Colonic infusion of RNase A suppressed gut motility and increased bone mass. These findings suggest gut ssRNA as a master determinant of systemic 5-HT levels, indicating the ssRNA-Piezo1 axis as a potential prophylactic target for treatment of bone and gut disorders.

Propulsive colonic contractions are mediated by inhibition-driven poststimulus responses that originate in interstitial cells of Cajal.

The peristaltic reflex is a fundamental behavior of the gastrointestinal (GI) tract in which mucosal stimulation activates propulsive contractions. The reflex occurs by stimulation of intrinsic primary afferent neurons with cell bodies in the myenteric plexus and projections to the lamina propria, distribution of information by interneurons, and activation of muscle motor neurons. The current concept is that excitatory cholinergic motor neurons are activated proximal to and inhibitory neurons are activated distal to the stimulus site. We found that atropine reduced, but did not block, colonic migrating motor complexes (CMMCs) in mouse, monkey, and human colons, suggesting a mechanism other than one activated by cholinergic neurons is involved in the generation/propagation of CMMCs. CMMCs were activated after a period of nerve stimulation in colons of each species, suggesting that the propulsive contractions of CMMCs may be due to the poststimulus excitation that follows inhibitory neural responses. Blocking nitrergic neurotransmission inhibited poststimulus excitation in muscle strips and blocked CMMCs in intact colons. Our data demonstrate that poststimulus excitation is due to increased Ca2+ transients in colonic interstitial cells of Cajal (ICC) following cessation of nitrergic, cyclic guanosine monophosphate (cGMP)-dependent inhibitory responses. The increase in Ca2+ transients after nitrergic responses activates a Ca2+-activated Cl− conductance, encoded by Ano1, in ICC. Antagonists of ANO1 channels inhibit poststimulus depolarizations in colonic muscles and CMMCs in intact colons. The poststimulus excitatory responses in ICC are linked to cGMP-inhibited cyclic adenosine monophosphate (cAMP) phosphodiesterase 3a and cAMP-dependent effects. These data suggest alternative mechanisms for generation and propagation of CMMCs in the colon.

Biomechanical increase in cervical esophageal wall tension during peristalsis.

During pharyngeal phase of swallowing, circumferential tension of the cervical esophagus (CTE) increases caused by a biomechanical process of laryngeal elevation pulling the cervical esophagus orad. The esophagus contracts longitudinally during esophageal peristalsis, therefore, we hypothesized that CTE increases during esophageal peristalsis by a biomechanical process. We investigated this hypothesis using 28 decerebrate cats instrumented with electromyographic (EMG) electrodes on the pharynx and esophagus, and esophageal manometry. We recorded CTE, distal esophageal longitudinal tension (DET), and orad laryngeal tension (OLT) using strain gauges. Peristalsis was stimulated by injecting saline into esophagus or nasopharynx. We investigated the effects of transecting the pharyngo-esophageal nerve (PEN), hypoglossal nerve (HG), or administering (10 mg/kg iv) hexamethonium (HEX). We found that the durations of CTE and DET increased and OLT decreased simultaneously during the total extent of esophageal peristalsis. CTE duration was highly correlated with DET but not esophageal EMG or manometry. The peak magnitudes of the DET and CTE were highly correlated. After HEX administration, peristalsis in the distal esophagus did not occur, and the duration of the CTE response decreased. PEN transection blocked the occurrence of cricopharyngeal or cervical esophageal response during peristalsis but had no significant effect on the CTE response. HG transection had no significant effect on CTE. We conclude that there is a significant CTE increase, independent of laryngeal elevation or esophageal muscle contraction, which occurs during esophageal peristalsis. This response is a biomechanical process caused by esophageal shortening that occurs during esophageal longitudinal contraction of esophageal peristalsis.NEW & NOTEWORTHY Circumferential tension of cervical esophagus (CTE) increases during esophageal peristalsis. CTE response is correlated with distal longitudinal tension on cervical esophagus during esophageal peristalsis but not laryngeal elevation or esophageal muscle contraction. CTE response is not blocked by transection of motor innervation of laryngeal elevating muscles or proximal esophagus but is temporally reduced after hexamethonium administration. We conclude that the CTE response is a biomechanical effect caused by longitudinal esophageal contraction during esophageal peristalsis.

Surface mapping of gastric motor functions using MRI: a comparative study between humans and rats.

The stomach's ability to store, mix, propel, and empty its content requires highly coordinated motor functions. However, current diagnostic tools cannot simultaneously assess these motor processes. This study aimed to use magnetic resonance imaging (MRI) to map multifaceted gastric motor functions, including accommodation, tonic and peristaltic contractions, and emptying, through a single noninvasive experiment for both humans and rats. Ten humans and 10 Sprague-Dawley rats consumed MRI-visible semisolid meals and underwent MRI scans. We used a surface model to analyze MRI data, capturing the deformation of the stomach wall on ingestion or during digestion. We inferred muscle activity, mapped motor processes, parcellated the stomach into functional regions, and revealed cross-species distinctions. In humans, both the fundus and antrum distended postmeal, followed by sustained tonic contractions to regulate intragastric pressure. Peristaltic contractions initiated from the distal fundus, including three concurrent wavefronts oscillating at 3.3 cycles/min and traveling at 1.7 to 2.9 mm/s. These motor functions facilitated linear gastric emptying with a 61-min half-time. In contrast, rats exhibited peristalsis from the midcorpus, showing two wavefronts oscillating at 5.0 cycles/min and traveling at 0.4 to 0.9 mm/s. For both species, motility features allowed functional parcellation of the stomach along a midcorpus division. This study maps region- and species-specific gastric motor functions. We demonstrate the value of MRI with surface modeling in understanding gastric physiology and its potential to become a new standard for clinical and preclinical investigations of gastric disorders at both individual and group levels.NEW & NOTEWORTHY A novel MRI technique can visualize how the stomach accommodates, mixes, and propels food for digestion in humans and animals alike. Digital models of gastric MRI reveal the functional maps, organization, and distinction of the stomach across individuals and species. This technique holds the unique potential to advance basic and clinical studies of functional gastric disorders.

Enhancing the diagnostic yield of esophageal manometry using distension-contraction plots of peristalsis and artificial intelligence.

Our prior study reveals that the distension-contraction profiles using high-resolution manometry impedance recordings can distinguish patients with dysphagia symptom but normal esophageal function testing ("functional dysphagia") from control subjects. The aim of this study was to determine the diagnostic value of the recording protocol used in our prior studies (10-mL swallows with subjects in the Trendelenburg position) against the standard clinical protocol (5-mL swallows with subjects in the supine position). We used advanced machine learning techniques and robust metrics for classification purposes. Studies were performed on 30 healthy subjects and 30 patients with functional dysphagia. A custom-built software was used to extract the relevant distension-contraction features of esophageal peristalsis. Ensemble methods, i.e., gradient boost, support vector machines (SVMs), and logit boost, were used as the primary machine learning algorithms. Although the individual contraction features were marginally different between the two groups, the distension features of peristalsis were significantly different. The receiver operating characteristic (ROC) curve values for the standard recording protocol and the distension features ranged from 0.74 to 0.82; they were significantly better for the protocol used in our prior studies, ranging from 0.81 to 0.91. The ROC curve values using three machine learning algorithms were far superior for the distension than the contraction features of esophageal peristalsis, revealing a value of 0.95 for the SVM algorithm. Current patient classification for esophageal motility disorders, based on the contraction phase of peristalsis, ignores a large number of patients who have an abnormality in the distension phase of peristalsis. Distension-contraction plots should be the standard for assessing esophageal peristalsis in clinical practice.NEW & NOTEWORTHY Our findings underscore the superiority of distension features over contraction metrics in diagnosing esophageal dysfunctions. By leveraging state-of-the-art machine learning techniques, our study highlights the diagnostic potential of distension-contraction plots of peristalsis. Implementation of these plots could significantly enhance the accuracy of identifying patients with esophageal motor disorders, advocating for their adoption as the standard in clinical practice.

A PhysioMechanical Model of Esophageal Function in Eosinophilic Esophagitis.

BACKGROUND & AIMS: Eosinophilic esophagitis (EoE) is characterized by eosinophilic inflammation, but also heterogeneous presentations involving fibrostenotic esophageal remodeling and esophageal dysmotility. We aimed to define and evaluate phenotypes of EoE using functional lumen imaging probe (FLIP) panometry (ie, a PhysioMechanical classification of EoE). METHODS: Patients with EoE who completed FLIP during endoscopy were included in a cross-sectional study. FLIP studies were analyzed for distensibility plateau and compliance of the esophageal body, maximum esophagogastric junction diameter, and contractile response pattern. These FLIP features were then applied to define PhysioMechanical classifications. RESULTS: A total of 215 patients with EoE (mean [standard deviation] age 38 [12] years; 31% female) were included. Seven PhysioMechanical classifications were identified that differed by various clinical characteristics, including symptom duration (P < .001) and Endoscopic EoE Reference Scores (EREFS) (P < .001). In particular, patients with "nonreactive fibrostenosis" (n = 14), had greater symptom duration (median [interquartile range] 20 [10-30] years) and more frequently had EREFS grade 2 or 3 ring scores (14 of 14 patients) than patients with a "normal" PhysioMechanical classification (symptom duration: 3 [1-8] years; 4 of 50 [8%] had EREFS grade 2 or 3 rings). In addition, among patients off treatment at cross-sectional evaluation (n = 46), there was a difference between PhysioMechanical classifications in future proton pump inhibitor (PPI) response rates (ie, achieving peak mucosal eosinophil count <15 per high-powered field after PPI treatment); P = .009. PPI response ranged from 87% (13 of 15 patients) with "isolated esophagogastric junction outflow obstruction" to 11% (1 of 9 patients) with "spastic-reactive fibrostenosis." CONCLUSIONS: Classifying PhysioMechanical esophageal function in EoE based on FLIP panometry features may facilitate defining disease severity and directing management in EoE.

Chronic intestinal pseudo-obstruction: associations with gut microbiota and genes expression of intestinal serotonergic pathway.

BACKGROUND: Pediatric chronic intestinal pseudo-obstruction (PIPO) is a rare disease characterized by symptoms and radiological signs suggestive of intestinal obstruction, in the absence of lumen-occluding lesions. It results from an extremely severe impairment of propulsive motility. The intestinal endocrine system (IES) jointly with the enteric nervous system (ENS) regulates secreto-motor functions via different hormones and bioactive messengers/neurotransmitters. The neurotransmitter 5-hydroxytryptamine (5-HT) (or serotonin) is linked to intestinal peristalsis and secretory reflexes. Gut microbiota and its interplay with ENS affect 5-HT synthesis, release, and the subsequent serotonin receptor activation. To date, the interplay between 5-HT and gut microbiota in PIPO remains largely unclear. This study aimed to assess correlations between mucosa associated microbiota (MAM), intestinal serotonin-related genes expression in PIPO. To this purpose, biopsies of the colon, ileum and duodenum have been collected from 7 PIPO patients, and 7 age-/sex-matched healthy controls. After DNA extraction, the MAM was assessed by next generation sequencing (NGS) of the V3-V4 region of the bacterial RNA 16 S, on an Illumina Miseq platform. The expression of genes implicated in serotoninergic pathway (TPH1, SLC6A4, 5-HTR3 and 5-HTR4) was established by qPCR, and correlations with MAM and clinical parameters of PIPO have been evaluated. RESULTS: Our results revealed that PIPO patients exhibit a MAM with a different composition and with dysbiosis, i.e. with a lower biodiversity and fewer less connected species with a greater number of non-synergistic relationships, compared to controls. qPCR results revealed modifications in the expression of serotonin-related intestinal genes in PIPO patients, when compared to controls. Correlation analysis do not reveal any kind of connection. CONCLUSIONS: For the first time, we report in PIPO patients a specific MAM associated to underlying pathology and an altered intestinal serotonin pathway. A possible dysfunction of the serotonin pathway, possibly related to or triggered by an altered microbiota, may contribute to dysmotility in PIPO patients. The results of our pilot study provide the basis for new biomarkers and innovative therapies targeting the microbiota or serotonin pathways in PIPO patients.

Peristalsis prevents ureteral dilation.

PURPOSE: The etiology of ureteral dilation in primary nonrefluxing, nonobstructing megaureters is still not well understood. Impaired ureteral peristalsis has been theorized as one of the contributing factors. However, ureteral peristalsis and its "normal" function is not well defined. In this study, using mathematical modeling techniques, we aim to better understand how ureteral peristalsis works. This is the first model to consider clinically observed, back-and-forth, cyclic wall longitudinal motion during peristalsis. We hypothesize that dysfunctional ureteral peristalsis, caused by insufficient peristaltic amplitudes (e.g., circular muscle dysfunction) and/or lack of ureteral wall longitudinal motion (e.g., longitudinal muscle dysfunction), promotes peristaltic reflux (i.e., retrograde flow of urine during an episode of peristalsis) and may result in urinary stasis, urine accumulation, and consequent dilation. METHODS: Based on lubrication theory in fluid mechanics, we developed a two-dimensional (planar) model of ureteral peristalsis. In doing so, we treated ureteral peristalsis as an infinite train of sinusoidal waves. We then analyzed antegrade and retrograde flows in the ureter under different bladder-kidney differential pressure and peristalsis conditions. RESULTS: There is a minimum peristaltic amplitude required to prevent peristaltic reflux. Ureteral wall longitudinal motion decreases this minimum required amplitude, increasing the nonrefluxing range of peristaltic amplitudes. As an example, for a normal bladder-kidney differential pressure of 5 cmH2 O, ureteral wall longitudinal motion increases nonrefluxing range of peristaltic amplitude by 65%. Additionally, ureteral wall longitudinal motion decreases refluxing volumetric flow rates. For a similar normal bladder pressure example of 5 cmH2 O, refluxing volumetric flow rate decreases by a factor of 18. Finally, elevated bladder pressure, not only increases the required peristaltic amplitude for reflux prevention but it increases maximum refluxing volumetric flow rates. For the case without wall longitudinal motion, as bladder-kidney differential pressure increases from 5 to 40 cmH2 O, minimum required peristaltic amplitude to prevent reflux increases by 40% while the maximum refluxing volumetric flow rate increases by approximately 100%. CONCLUSION: The results presented in this study show how abnormal ureteral peristalsis, caused by the absence of wall longitudinal motion and/or lack of sufficient peristaltic amplitudes, facilitates peristaltic reflux and retrograde flow. We theorize that this retrograde flow can lead to urinary stasis and urine accumulation in the ureters, resulting in ureteral dilation seen on imaging studies and elevated infection risk. Our results also show how chronically elevated bladder pressures are more susceptible to such refluxing conditions that could lead to ureteral dilation.

Efficacy of Glycicumarin and Isoliquiritigenin in Suppressing Colonic Peristalsis in Both an Animal Model and a Clinical Trial.

Patients with diarrhea-predominant irritable bowel syndrome (IBS-D) show excessive peristalsis, and antispasmodic agents may be useful therapeutic agents. There are few reports on the use of Kampo medicines for the treatment of IBS-D. Shakuyakukanzoto (SKT) is a Kampo medicine that is effective against abdominal pain. We examined the relationship between SKT and intestinal peristalsis in an animal model and a prospective study. In the animal model, SKT and its components were administered from the serosal side of the colon and colonic peristalsis was evaluated using intraluminal pressure and spatiotemporal mapping before and after the administration of SKT and its components. In this clinical trial, we used abdominal ultrasonography (US) to obtain long-axis images of the sigmoid colon of 11 patients. The frequency of intestinal peristalsis was measured using US in five patients with SKT and six patients without medication after the ingestion of a test meal. The primary outcome was the frequency of peristalsis. The Clinical Trial Registry Website (Trial No. UMIN-CTR; UMIN000051547). In the animal model, peony did not suppress peristalsis frequency, but SKT (p = 0.005) and glycyrrhiza (p = 0.001) significantly suppressed peristalsis frequency compared with saline and peony. Among the glycyrrhiza components, glycycoumarin and isoliquiritigenin suppressed the peristalsis frequency compared to dimethyl sulfoxide (control) (p = 0.001, 0.01, respectively). In a clinical trial, peristalsis was significantly suppressed after oral administration in patients taking SKT (p = 0.03). Administration of SKT was found to inhibit colonic peristalsis, with glycicumarin and isoliquiritigenin being particularly relevant among its components.

An analytical and comparative study of swallowing in a tumor-infected oesophagus: a mathematical model.

This study discusses non-steady effects encountered in peristaltic flows in oesophagus. The purpose of this communication is to evolve a mechanism to diagnose tumor in an oesophagus mathematically. The tumor is modelled by generic bump function of certain height and width. The method of solution follows long wavelength and low-Reynolds number approximations for unsteady flow, while integrations have been performed numerically in order to plot graphs, which reveal various characteristics of the flow. The goal is to assess how pressure varies across the tumor's width. The spatial, as well as temporal, dependence of pressure has been studied in the laboratory frame of reference. The pressure distribution for tumor-infected oesophagus is compared with that of normal oesophagus. An intensified pressure is obtained in the presence of tumor. The interruption while swallowing through benign oesophageal tumor is confirmed by an abrupt pressure rise across the tumor's width. Tumor position also plays a significant role whether it is at contraction or relaxation of walls. Additionally, wall-shear-stress, volumetric flow rate and streamlines have also been described and compared with that without tumor growth. The expressions corresponding to all the physical quantities are computed numerically. Further, this model may also be implemented to the two-dimensional channel flow for an industrial application.

A Mechanics-Based Perspective on the Function of Human Sphincters During Functional Luminal Imaging Probe Manometry.

Functional luminal imaging probe (FLIP) is used to measure cross-sectional area (CSA) and pressure at sphincters. It consists of a catheter surrounded by a fluid filled cylindrical bag, closed on both ends. Plotting the pressure-CSA hysteresis of a sphincter during a contraction cycle, which is available through FLIP testing, offers information on its functionality, and can provide diagnostic insights. However, limited work has been done to explain the mechanics of these pressure-CSA loops. This work presents a consolidated picture of pressure-CSA loops of different sphincters. Clinical data reveal that although sphincters have a similar purpose (controlling the flow of liquids and solids by opening and closing), two different pressure-CSA loop patterns emerge: negative slope loop (NSL) and positive slope loop (PSL). We show that the loop type is the result of an interplay between (or lack thereof) two mechanical modes: (i) neurogenic mediated relaxation of the sphincter muscle or pulling applied by external forces, and (ii) muscle contraction proximal to the sphincter which causes mechanical distention. We conclude that sphincters which only function through mechanism (i) exhibition NSL whereas sphincters which open as a result of both (i) and (ii) display a PSL. This work provides a fundamental mechanical understanding of human sphincters. This can be used to identify normal and abnormal phenotypes for the different sphincters and help in creating physiomarkers based on work calculation.

Revealing the material basis and mechanism for the inhibition of intestinal peristalsis by Zingiber officinale Roscoe through integrated metabolomics, serum pharmacochemistry, and network pharmacology.

Abnormal relaxation and contraction of intestinal smooth muscle can cause various intestinal diseases. Diarrhea is a common and important public health problem worldwide in epidemiology. Zingiber officinale Roscoe (fresh ginger) has been found to treat diarrhea, but the material basis and mechanism of action that inhibits intestinal peristalsis remain unclear. Metabolomics and serum pharmacology were used to identify differential metabolites, metabolic pathways, and pharmacodynamic substances, and were then combined with network pharmacology to explore the potential targets of ginger that inhibit intestinal peristalsis during diarrhea treatment, and the targets identified were verified using molecular docking and molecular dynamic simulation. We found that 25 active components of ginger (the six most relevant components), 35 potential key targets (three core targets), 40 differential metabolites (four key metabolites), and four major metabolic pathways were involved in the process by which ginger inhibits intestinal peristalsis during diarrhea treatment. This study reveals the complex mechanism of action and pharmacodynamic material basis of ginger in the inhibition of intestinal peristalsis, and this information helps in the development of new Chinese medicine to treat diarrhea and lays the foundation for the clinical application of ginger.

Effects of Phloroglucinol on Embryo Transfer: A Systematic Review and Meta-Analysis.

INTRODUCTION: Phloroglucinol may be able to improve embryo transfer outcomes. We aimed to systematically evaluate the effects of phloroglucinol on embryo transfer outcomes. METHODS: The databases searched were PubMed, Ovid MEDLINE, Web of Science, Wanfang, CQVIP, China National Knowledge Infrastructure, and ClinicalTrials.gov. The last search was on February 7, 2023. The included studies were written in English or Chinese. Randomized controlled trials and cohort studies aiming to assess the effect of phloroglucinol on embryo transfer outcomes were included. The studies reported at least one of the primary outcomes (biochemical pregnancy rate, clinical pregnancy rate, and live birth rate). The odds ratio (OR) and 95% confidence interval (CI) were calculated. A random-effects or fixed model was used where applicable to estimate the results. RESULTS: Seventeen articles reporting 5,953 cycles were included. Biochemical pregnancy rate (OR = 1.58, 95% CI = 1.20-2.08, I2 = 71%), clinical pregnancy rate (OR = 1.69, 95% CI = 1.35-2.10, I2 = 64%), and live birth rate (OR = 1.45, 95% CI = 1.23-1.71, I2 = 36%) were improved by phloroglucinol. Less miscarriage (OR = 0.46, 95% CI = 0.35-0.60, I2 = 0%), less ectopic pregnancy (OR = 0.45, 95% CI = 0.28-0.72, I2 = 0%), higher implantation rate (OR = 1.45, 95% CI = 1.24-1.71, I2 = 62%) but more multiple pregnancy rate (OR = 1.48, 95% CI = 1.13-1.94, I2 = 0%) were induced by phloroglucinol. Endometrial peristaltic waves were improved by phloroglucinol (OR = 22.87, 95% CI = 5.52-94.74, I2 = 72%). CONCLUSION: Phloroglucinol may improve the outcomes of embryo transfer, including biochemical pregnancy, clinical pregnancy, and live birth rates. Further studies are warranted.

Daphnia magna digestive activity is differentially altered when exposed to equally turbid waters caused by either suspended sediment or suspended microplastics.

Turbidity can be a result of suspended natural particles, such as sediment, or anthropogenic particles such as microplastics. This study assessed whether Daphnia magna, a pelagic filter feeder known to ingest suspended particles, have an altered response to equally turbid environments caused by the presence of either suspended bentonite or suspended polyethylene microplastics. Compared to controls, daphnids exposed to suspended bentonite maintained their feeding efficiency and increased their digestive activity, as measured by mandibular movement, peristalsis, and expulsion, to pass bentonite through the digestive tract. The same effects were not seen in microplastic-exposed individuals, in which feeding efficiency was decreased and only peristaltic movement was increased but without a coordinated increase in expulsion, suggesting that microplastics do not have the same ability as bentonite to pass through the digestive tract. This study highlights the need to discern the identities of particulates contributing to turbid environments as different particles, even of the same size, can have different effects on filter feeders, which inherently ingest suspended particles.

Effect of marination in lemon juice on beef tenderization and in vitro gastric digestibility.

BACKGROUND: There is limited knowledge regarding digestion and absorption of nutrients after cooked marinated meat is ingested. Most of the previous studies on food gastric digestion have focused on chemical digestion and did not reflect upon physical digestion driven by peristalsis. In the present study, we examined the effects of marinating beef in lemon juice on gastric digestibility using a human gastric digestion simulator (GDS) that mimics peristaltic motion called antral contraction waves. RESULTS: Beef thigh slices were marinated in 100% lemon juice for 1 h and then grilled; an image of a stained tissue sample revealed that muscle tissue contraction (i.e. that usually occurs upon cooking) was suppressed. The measurement of physical properties using a rheometer and texture analyzer showed that the meat marinated in lemon juice had a soft texture. In vitro digestion experiments using the GDS revealed that the extent of both physical digestion driven by peristalsis and chemical digestion catalyzed by digestive enzymes was enhanced by the lemon juice marinade. CONCLUSION: The results of the present study suggest that marinating beef in lemon juice affects nutrient digestibility. An integrated evaluation of tissue structure, physical properties and GDS digestion to analyze meat digestion would enhance our understanding of the effects of seasoning and cooking methods on meat. © 2023 Society of Chemical Industry.

An evolutionarily conserved pacemaker role for HCN ion channels in smooth muscle.

Although hyperpolarization-activated cation (HCN) ion channels are well established to underlie cardiac pacemaker activity, their role in smooth muscle organs remains controversial. HCN-expressing cells are localized to renal pelvic smooth muscle (RPSM) pacemaker tissues of the murine upper urinary tract and HCN channel conductance is required for peristalsis. To date, however, the Ih pacemaker current conducted by HCN channels has never been detected in these cells, raising questions on the identity of RPSM pacemakers. Indeed, the RPSM pacemaker mechanisms of the unique multicalyceal upper urinary tract exhibited by humans remains unknown. Here, we developed immunopanning purification protocols and demonstrate that 96% of isolated HCN+ cells exhibit Ih . Single-molecule STORM to whole-tissue imaging showed HCN+ cells express single HCN channels on their plasma membrane and integrate into the muscular syncytium. By contrast, PDGFR-α+ cells exhibiting the morphology of ICC gut pacemakers were shown to be vascular mural cells. Translational studies in the homologous human and porcine multicalyceal upper urinary tracts showed that contractions and pacemaker depolarizations originate in proximal calyceal RPSM. Critically, HCN+ cells were shown to integrate into calyceal RPSM pacemaker tissues, and HCN channel block abolished electrical pacemaker activity and peristalsis of the multicalyceal upper urinary tract. Cumulatively, these studies demonstrate that HCN ion channels play a broad, evolutionarily conserved pacemaker role in both cardiac and smooth muscle organs and have implications for channelopathies as putative aetiologies of smooth muscle disorders. KEY POINTS: Pacemakers trigger contractions of involuntary muscles. Hyperpolarization-activated cation (HCN) ion channels underpin cardiac pacemaker activity, but their role in smooth muscle organs remains controversial. Renal pelvic smooth muscle (RPSM) pacemakers trigger contractions that propel waste away from the kidney. HCN+ cells localize to murine RPSM pacemaker tissue and HCN channel conductance is required for peristalsis. The HCN (Ih ) current has never been detected in RPSM cells, raising doubt whether HCN+ cells are bona fide pacemakers. Moreover, the pacemaker mechanisms of the unique multicalyceal RPSM of higher order mammals remains unknown. In total, 97% of purified HCN+ RPSM cells exhibit Ih . HCN+ cells integrate into the RPSM musculature, and pacemaker tissue peristalsis is dependent on HCN channels. Translational studies in human and swine demonstrate HCN channels are conserved in the multicalyceal RPSM and that HCN channels underlie pacemaker activity that drives peristalsis. These studies provide insight into putative channelopathies that can underlie smooth muscle dysfunction.

Neural targets of the enteric dopaminergic system in regulating motility of rat proximal colon.

In isolated segments of the rat proximal colon, the dopamine reuptake inhibitor GBR 12909 (GBR) causes a dilatation, while the D1-like receptor antagonist SCH 23390 (SCH) induces a tonic constriction, suggesting that neurally released dopamine tonically stimulates enteric inhibitory efferent neurons. Here, the targets of the enteric dopaminergic neurons were investigated. Cannulated segments of rat proximal colon were bathed in physiological salt solution and luminally perfused with 0.9% saline, while all drugs were applied to the bath. Spatio-temporal maps of colonic motility were constructed from video recordings of peristaltic contractions, and the maximum diameter was measured as an index of colonic contractility. GBR (1 µM)-induced dilatations of colonic segments were prevented by SCH (5 µM), L-nitro arginine (L-NA; 100 µM), a nitric oxide synthase inhibitor, or tetrodotoxin (0.6 µM). In contrast, constrictions induced by a higher concentration of SCH (20 µM) were unaffected by either L-NA or tetrodotoxin. The vasoactive intestinal peptide (VIP) receptor antagonist VIP10-28 (3 µM) or P2Y1 receptor antagonist MRS 2500 (1 µM) had no effect on either the GBR-induced dilatation or the SCH-induced constriction. In colonic segments that had been pretreated with 6-hydroxydopamine (100 µM, 3 h) to deplete enteric dopamine, GBR failed to increase the colonic diameter, while SCH was still capable of constricting colonic segments. Enteric dopaminergic neurons appear to project to nitrergic neurons to dilate the proximal colon by activating neuronal D1-like receptors. In addition, constitutively activated D1-like receptors expressed in cells yet to be determined may provide a tonic inhibition on colonic constrictions.

Rapid Prototypable Biomimetic Peristalsis Bioreactor Capable of Concurrent Shear and Multi-Axial Strain.

Peristalsis is a nuanced mechanical stimulus comprised of multi-axial strain (radial and axial strain) and shear stress. Forces associated with peristalsis regulate diverse biological functions including digestion, reproductive function, and urine dynamics. Given the central role peristalsis plays in physiology and pathophysiology, we were motivated to design a bioreactor capable of holistically mimicking peristalsis. We engineered a novel rotating screw-drive based design combined with a peristaltic pump, in order to deliver multi-axial strain and concurrent shear stress to a biocompatible polydimethylsiloxane (PDMS) membrane "wall." Radial indentation and rotation of the screw drive against the wall demonstrated multi-axial strain evaluated via finite element modeling. Experimental measurements of strain using piezoelectric strain resistors were in close alignment with model-predicted values (15.9 ± 4.2% vs. 15.2% predicted). Modeling of shear stress on the "wall" indicated a uniform velocity profile and a moderate shear stress of 0.4 Pa. Human mesenchymal stem cells (hMSCs) seeded on the PDMS "wall" and stimulated with peristalsis demonstrated dramatic changes in actin filament alignment, proliferation, and nuclear morphology compared to static controls, perfusion, or strain, indicating that hMSCs sensed and responded to peristalsis uniquely. Lastly, significant differences were observed in gene expression patterns of calponin, caldesmon, smooth muscle actin, and transgelin, corroborating the propensity of hMSCs toward myogenic differentiation in response to peristalsis. Collectively, our data suggest that the peristalsis bioreactor is capable of generating concurrent multi-axial strain and shear stress on a "wall." hMSCs experience peristalsis differently than perfusion or strain, resulting in changes in proliferation, actin fiber organization, smooth muscle actin expression, and genetic markers of differentiation. The peristalsis bioreactor device has broad utility in the study of development and disease in several organ systems.

Uterine contractile activity in healthy women throughout the menstrual cycle measured using a novel quantitative two-dimensional transvaginal ultrasound speckle tracking method.

RESEARCH QUESTION: To explore normal uterine contractile function across the menstrual cycle using a novel quantitative ultrasound method. DESIGN: This multicentre prospective observational study took place in three European centres from 2014 to 2022. Uterine contraction frequency (contractions/minute), amplitude, direction (cervix-to-fundus, C2F; fundus-to-cervix; F2C), velocity and coordination were investigated. Features were extracted from transvaginal ultrasound recordings (TVUS) using speckle tracking. Premenopausal women ≥18 years of age, with normal, natural menstrual cycles were included. A normal cycle was defined as: regular (duration 28 ± 2 days), no dysmenorrhoea, no menometrorrhagia. Four-minute TVUS were performed during the menstrual phase, mid-follicular, late follicular phase, early luteal phase and/or late luteal phase. Of the 96 recordings available from 64 women, 70 were suitable for inclusion in the analysis. RESULTS: Contraction frequency (for the posterior wall) and velocity (for the anterior uterine wall in the F2C direction) were highest in the late follicular phase and lowest in the menstrual and late luteal phases (1.61 versus 1.31 and 1.35 contractions/min, P < 0.001 and 0.81 versus 0.67 and 0.62 mm/s, P < 0.001, respectively). No significant difference was found for contraction amplitude. Contraction coordination (simultaneous contraction of the anterior and posterior walls in the same direction) was least coordinated in the mid-follicular phase (P = 0.002). CONCLUSIONS: This is the first study to objectively measure uterine contraction features in healthy women during the natural menstrual cycle on TVUS. Likewise, it introduces contraction coordination as a specific feature of uterine peristalsis. Differences in uterine contractility across the menstrual cycle are confirmed, with highest activity seen in the late follicular phase, and lowest in the late luteal phase.

Indwelling stents cause obstruction and induce ureteral injury and fibrosis in a porcine model.

OBJECTIVES: To investigate global changes in ureters at the transcriptional, translational and functional levels, both while stents are indwelling and after removal and recovery, and to study the effects of targeting pathways that play a potential role. METHODS: Pig ureters were stented for varying amounts of time (48 h, 72 h, 14 days) and the impact on peristalsis, dilatation and hydronephrosis were assessed. RNAseq, proteomic, histological and smooth muscle (SM) function analyses were performed on ureteric and kidney tissues to assess changes induced by stenting and recovery. Pathway analysis was performed using Ingenuity Pathway Analysis software. To study the impact of possible interventions, the effects of erythropoeitin (EPO) and a Gli1 inhibitor were assessed. RESULTS: Stenting triggers massive ureteric dilatation, aperistalsis and moderate hydronephrosis within 48 h. Pathways associated with obstruction, fibrosis and kidney injury were upregulated by stenting. Increased expression of GLI1, clusterin-α (a kidney injury marker) and collagen 4A2 (a fibrosis marker) was found in stented vs contralateral unstented ureters. EPO did not improve peristalsis or contraction force but did decrease non-purposeful spasming seen exclusively in stented ureters. Tamsulosin administration increased contractility but not rate of peristalsis in stented ureters. CONCLUSIONS: Ureters respond to stents similarly to how they respond to an obstruction, that is, with activation of pathways associated with hydronephrosis, fibrosis and kidney injury. This is driven by significant dilatation and associated ureteric SM dysfunction. EPO and tamsulosin induced mild favourable changes in SM physiology, suggesting that targeting specific pathways has potential to address stent-induced complications.