Role of mechanoregulation in mast cell-mediated immune inflammation of the smooth muscle in the pathophysiology of esophageal motility disorders.

Major esophageal disorders involve obstructive transport of bolus to the stomach, causing symptoms of dysphagia and impaired clearing of the refluxed gastric contents. These may occur due to mechanical constriction of the esophageal lumen or loss of relaxation associated with deglutitive inhibition, as in achalasia-like disorders. Recently, immune inflammation has been identified as an important cause of esophageal strictures and the loss of inhibitory neurotransmission. These disorders are also associated with smooth muscle hypertrophy and hypercontractility, whose cause is unknown. This review investigated immune inflammation in the causation of smooth muscle changes in obstructive esophageal bolus transport. Findings suggest that smooth muscle hypertrophy occurs above the obstruction and is due to mechanical stress on the smooth muscles. The mechanostressed smooth muscles release cytokines and other molecules that may recruit and microlocalize mast cells to smooth muscle bundles, so that their products may have a close bidirectional effect on each other. Acting in a paracrine fashion, the inflammatory cytokines induce genetic and epigenetic changes in the smooth muscles, leading to smooth muscle hypercontractility, hypertrophy, and impaired relaxation. These changes may worsen difficulty in the esophageal transport. Immune processes differ in the first phase of obstructive bolus transport, and the second phase of muscle hypertrophy and hypercontractility. Moreover, changes in the type of mechanical stress may change immune response and effect on smooth muscles. Understanding immune signaling in causes of obstructive bolus transport, type of mechanical stress, and associated smooth muscle changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.NEW & NOTEWORTHY Esophageal disorders such as esophageal stricture or achalasia, and diffuse esophageal spasm are associated with smooth muscle hypertrophy and hypercontractility, above the obstruction, yet the cause of such changes is unknown. This review suggests that smooth muscle obstructive disorders may cause mechanical stress on smooth muscle, which then secretes chemicals that recruit, microlocalize, and activate mast cells to initiate immune inflammation, producing functional and structural changes in smooth muscles. Understanding the immune signaling in these changes may help pathophysiology-based prevention and targeted treatment of esophageal motility disorders.

Differential Myosin 5a splice variants in innervation of pelvic organs.

Introduction: Myosin proteins interact with filamentous actin and translate the chemical energy generated by ATP hydrolysis into a wide variety of mechanical functions in all cell types. The classic function of conventional myosins is mediation of muscle contraction, but myosins also participate in processes as diverse as exocytosis/endocytosis, membrane remodeling, and cytokinesis. Myosin 5a (Myo5a) is an unconventional motor protein well-suited to the processive transport of diverse molecular cargo within cells and interactions with multiprotein membrane complexes that facilitate exocytosis. Myo5a includes a region consisting of six small alternative exons which can undergo differential splicing. Neurons and skin melanocytes express characteristic splice variants of Myo5a, which are specialized for transport processes unique to those cell types. But less is known about the expression of Myo5a splice variants in other tissues, their cargos and interactive partners, and their regulation. Methods: In visceral organs, neurotransmission-induced contraction or relaxation of smooth muscle is mediated by Myo5a. Axons within urogenital organs and distal colon of rodents arise from cell bodies located in the major pelvic ganglion (MPG). However, in contrast to urogenital organs, the distal colon also contains soma of the enteric nervous system. Therefore, the rodent pelvic organs provide an opportunity to compare the expression of Myo5a splice variants, not only in different tissues innervated by the pelvic nerves, but also in different subcellular compartments of those nerves. This study examines the expression and distribution of Myo5a splice variants in the MPG, compared to the bladder, corpus cavernosum of the penis (CCP) and distal colon using immunohistochemistry and mRNA analyses. Results/discussion: We report detection of characteristic Myo5a variants in these tissues, with bladder and CCP displaying a similar variant pattern but one which differed from that of distal colon. In all three organs, Myo5a variants were distinct compared to the MPG, implying segregation of one variant within nerve soma and its exclusion from axons. The expression of distinct Myo5a variant arrays is likely to be adaptive, and to underlie specific functions fulfilled by Myo5a in those particular locations.

Myosin 5a in the Urinary Bladder: Localization, Splice Variant Expression, and Functional Role in Neurotransmission.

Dysregulation of neurotransmission is a feature of several prevalent lower urinary tract conditions, but the mechanisms regulating neurotransmitter release in the bladder are not completely understood. The unconventional motor protein, Myosin 5a, transports neurotransmitter-containing synaptic vesicles along actin fibers towards the varicosity membrane, tethering them at the active zone prior to reception of a nerve impulse. Our previous studies indicated that Myosin 5a is expressed and functionally relevant in the peripheral nerves of visceral organs such as the stomach and the corpora cavernosa. However, its potential role in bladder neurotransmission has not previously been investigated. The expression of Myosin 5a was examined by quantitative PCR and restriction analyses in bladders from DBA (dilute-brown-nonagouti) mice which express a Myosin 5a splicing defect and in control mice expressing the wild-type Myosin 5a allele. Functional differences in contractile responses to intramural nerve stimulation were examined by ex vivo isometric tension analysis. Data demonstrated Myosin 5a localized in cholinergic nerve fibers in the bladder and identified several Myosin 5a splice variants in the detrusor. Full-length Myosin 5a transcripts were less abundant and the expression of splice variants was altered in DBA bladders compared to control bladders. Moreover, attenuation of neurally-mediated contractile responses in DBA bladders compared to control bladders indicates that Myosin 5a facilitates excitatory neurotransmission in the bladder. Therefore, the array of Myosin 5a splice variants expressed, and the abundance of each, may be critical parameters for efficient synaptic vesicle transport and neurotransmission in the urinary bladder.

Expression of Myosin 5a splice variants in murine stomach.

BACKGROUND: The motor protein, Myosin 5a (Myo5a) is known to play a role in inhibitory neurotransmission in gastric fundus. However, there is no information regarding the relative expression of total Myo5a, or of its alternative exon splice variants, across the stomach. This study investigated the differential distribution of Myo5a variants expressed within distinct anatomical regions of murine stomach. METHODS: The distribution of Myo5a protein and mRNA in the stomach was assessed by immunofluorescence microscopy and fluorescent in situ hybridization. Quantitative PCR, restriction enzyme analysis, and electrophoresis were used to identify Myo5a splice variants and quantify their expression levels in the fundus, body, antrum, and pylorus. KEY RESULTS: Myo5a protein colocalized with ßIII-Tubulin in the myenteric plexus, and with synaptophysin in nerve fibers. Total Myo5a mRNA expression was lower in pylorus than in antrum, body, or fundus (p < 0.001), which expressed equivalent amounts of Myo5a. However, Myo5a splice variants were differentially expressed across the stomach. While the ABCE splice variant predominated in the antrum and body regions, the ACEF/ACDEF variants were enriched in fundus and pylorus. CONCLUSIONS AND INFERENCES: Myo5a splice variants varied in their relative expression across anatomically distinguishable stomach regions and might mediate distinct physiological functions in gastric neurotransmission.

Rapid gastric emptying in diabetes mellitus: Pathophysiology and clinical importance.

Although slow gastric emptying (gastroparesis) is a well-known complication of chronic hyperglycemia in diabetes mellitus (DM), it recently has become clear that rapid gastric emptying also is a frequent and important diabetic complication. In contrast, acute hyperglycemia causes slow gastric emptying, and acute hypoglycemia causes rapid gastric emptying. Rapid gastric emptying is frequent in T2DM; however, it may also occur in T1DM, particularly in the early stages of the disease, but may persist even into late stages. Recent studies suggest that usually, the stomach restricts the emptying of nutrients to 1-4 kcals/min. This restriction is due to the action of the gastric 'braking' hormones such as GLP-1, leptin, and amylin acting via the gastric inhibitory vagal motor circuit (GIVMC). Disruption of this braking system leads to rapid gastric emptying. Acute hyperglycemia also slows gastric emptying by stimulating the GIVMC, while acute hypoglycemia causes rapid gastric emptying by stimulating the gastric excitatory vagal motor circuit (GEVMC). In contrast, chronic hyperglycemia causes rapid gastric emptying by inducing oxidative stress in the stomach wall that disrupts inhibitory neuromuscular transmission and increases the contractility of the smooth muscle, while chronic hyperglycemia may also cause slow gastric emptying via severe inflammatory stress caused by proinflammatory macrophages and reduce contractility of the smooth muscle. There is a bidirectional relationship between blood glucose and gastric emptying. Thus, rapid gastric emptying may lead to a sizeable postprandial spike, and slow gastric emptying may blunt it. Postprandial hyperglycemia is involved in the development, progression, and complications of DM. Correction of fast gastric emptying involves agents that activate GIVMC and the use of gastric 'braking' hormones or their analogs. Recognition and treatment of rapid gastric emptying may contribute to better management of postprandial hyperglycemia and prevention of some diabetic complications.

Advances in the physiology of gastric emptying.

There have been many recent advances in the understanding of various aspects of the physiology of gastric motility and gastric emptying. Earlier studies had discovered the remarkable ability of the stomach to regulate the timing and rate of emptying of ingested food constituents and the underlying motor activity. Recent studies have shown that two parallel neural circuits, the gastric inhibitory vagal motor circuit (GIVMC) and the gastric excitatory vagal motor circuit (GEVMC), mediate gastric inhibition and excitation and therefore the rate of gastric emptying. The GIVMC includes preganglionic cholinergic neurons in the DMV and the postganglionic inhibitory neurons in the myenteric plexus that act by releasing nitric oxide, ATP, and peptide VIP. The GEVMC includes distinct gastric excitatory preganglionic cholinergic neurons in the DMV and postganglionic excitatory cholinergic neurons in the myenteric plexus. Smooth muscle is the final target of these circuits. The role of the intramuscular interstitial cells of Cajal in neuromuscular transmission remains debatable. The two motor circuits are differentially regulated by different sets of neurons in the NTS and vagal afferents. In the digestive period, many hormones including cholecystokinin and GLP-1 inhibit gastric emptying via the GIVMC, and in the inter-digestive period, hormones ghrelin and motilin hasten gastric emptying by stimulating the GEVMC. The GIVMC and GEVMC are also connected to anorexigenic and orexigenic neural pathways, respectively. Identification of the control circuits of gastric emptying may provide better delineation of the pathophysiology of abnormal gastric emptying and its relationship to satiety signals and food intake.

Effect of Hyperglycemia on Purinergic and Nitrergic Inhibitory Neuromuscular Transmission in the Antrum of the Stomach: Implications for Fast Gastric Emptying.

BACKGROUND: Hyperglycemia has been reported to enhance vagovagal reflex that causes the release of inhibitory neurotransmitter, nitric oxide (NO), at the neuromuscular junction in the antrum to relax the antrum and slow gastric emptying by stimulating glucose-sensitive afferent neurons. However, hyperglycemia has also been reported to cause fast gastric emptying that may be due to suppression of the inhibitory motor neurons. AIMS: The purpose of the present study was to investigate changes in inhibitory neuromuscular transmission in the gastric antrum due to hyperglycemia. METHODS: Inhibitory electrical junction potentials were recorded from gastric antral muscle strips, using intracellular electrodes under non-adrenergic, non-cholinergic conditions. Studies were performed in non-hyperglycemic NOD (NH-NOD), NOD mice as they develop hyperglycemia (H-NOD) and their age-matched controls. The purinergic inhibitory junction potential (pIJP) and nitrergic IJP (nIJP) were isolated pharmacologically. RESULTS: The control pIJP was large, around -18 mV and nIJP was small, around -9 mV. In NH-NOD the IJPs were not affected, but in H-NOD pIJP was nearly abolished and nIJP was significantly reduced. In H-NOD mice, membrane hyperpolarization caused by exogenous α,ß-MeATP or diethylenetriamine NO adduct was similar to that in wild-type controls (P > 0.05). H-NOD smooth muscles were significantly depolarized as compared to NH-NOD smooth muscles. CONCLUSION: These observations show that hyperglycemia causes suppression of purinergic and nitrergic transmission by acting on the motor neurons that form the last neuron in the vagovagal circuit. Moreover, the loss the neurotransmission is due to a defect in neurotransmitter release rather than a defect in signal transduction. Hyperglycemia also causes depolarization of smooth muscles that may increase their excitability.

Dysfunctional tear syndrome: dry eye disease and associated tear film disorders - new strategies for diagnosis and treatment.

Dysfunctional tear syndrome (DTS) is a common and complex condition affecting the ocular surface. The health and normal functioning of the ocular surface is dependent on a stable and sufficient tear film. Clinician awareness of conditions affecting the ocular surface has increased in recent years because of expanded research and the publication of diagnosis and treatment guidelines pertaining to disorders resulting in DTS, including the Delphi panel treatment recommendations for DTS (2006), the International Dry Eye Workshop (DEWS) (2007), the Meibomian Gland Dysfunction (MGD) Workshop (2011), and the updated Preferred Practice Pattern guidelines from the American Academy of Ophthalmology pertaining to dry eye and blepharitis (2013). Since the publication of the existing guidelines, new diagnostic techniques and treatment options that provide an opportunity for better management of patients have become available. Clinicians are now able to access a wealth of information that can help them obtain a differential diagnosis and treatment approach for patients presenting with DTS. This review provides a practical and directed approach to the diagnosis and treatment of patients with DTS, emphasizing treatment that is tailored to the specific disease subtype as well as the severity of the condition.

Myosin Va plays a role in nitrergic smooth muscle relaxation in gastric fundus and corpora cavernosa of penis.

The intracellular motor protein myosin Va is involved in nitrergic neurotransmission possibly by trafficking of neuronal nitric oxide synthase (nNOS) within the nerve terminals. In this study, we examined the role of myosin Va in the stomach and penis, proto-typical smooth muscle organs in which nitric oxide (NO) mediated relaxation is critical for function. We used confocal microscopy and co-immunoprecipitation of tissue from the gastric fundus (GF) and penile corpus cavernosum (CCP) to localize myosin Va with nNOS and demonstrate their molecular interaction. We utilized in vitro mechanical studies to test whether smooth muscle relaxations during nitrergic neuromuscular neurotransmission is altered in DBA (dilute, brown, non-agouti) mice which lack functional myosin Va. Myosin Va was localized in nNOS-positive nerve terminals and was co-immunoprecipitated with nNOS in both GF and CCP. In comparison to C57BL/6J wild type (WT) mice, electrical field stimulation (EFS) of precontracted smooth muscles of GF and CCP from DBA animals showed significant impairment of nitrergic relaxation. An NO donor, Sodium nitroprusside (SNP), caused comparable levels of relaxation in smooth muscles of WT and DBA mice. These normal postjunctional responses to SNP in DBA tissues suggest that impairment of smooth muscle relaxation resulted from inhibition of NO synthesis in prejunctional nerve terminals. Our results suggest that normal physiological processes of relaxation of gastric and cavernosal smooth muscles that facilitate food accommodation and penile erection, respectively, may be disrupted under conditions of myosin Va deficiency, resulting in complications like gastroparesis and erectile dysfunction.

Gastroenterology's editors-in-chief: historical and personal perspectives of their editorships.

Fourteen editors-in-chiefs have steered Gastroenterologyto success since its inception in 1943. Five (Alvarez, Ivy, Aaron, Grossman, and Donaldson) are no longer with us. Their personalities and editorships, along with those of Marvin Sleisenger, are presented by their admirers. Fordtran, Ockner, Goyal, LaRusso, Podolsky, Brenner, Rustgi, and Omary describe their own backgrounds, experiences, and personal reflections on serving as editor-in-chief of Gastroenterology.

Structure activity relationship of synaptic and junctional neurotransmission.

Chemical neurotransmission may include transmission to local or remote sites. Locally, contact between 'bare' portions of the bulbous nerve terminal termed a varicosity and the effector cell may be in the form of either synapse or non-synaptic contact. Traditionally, all local transmissions between nerves and effector cells are considered synaptic in nature. This is particularly true for communication between neurons. However, communication between nerves and other effectors such as smooth muscles has been described as nonsynaptic or junctional in nature. Nonsynaptic neurotransmission is now also increasingly recognized in the CNS. This review focuses on the relationship between structure and function that orchestrate synaptic and junctional neurotransmissions. A synapse is a specialized focal contact between the presynaptic active zone capable of ultrafast release of soluble transmitters and the postsynaptic density that cluster ionotropic receptors. The presynaptic and the postsynaptic areas are separated by the 'closed' synaptic cavity. The physiological hallmark of the synapse is ultrafast postsynaptic potentials lasting milliseconds. In contrast, junctions are juxtapositions of nerve terminals and the effector cells without clear synaptic specializations and the junctional space is 'open' to the extracellular space. Based on the nature of the transmitters, postjunctional receptors and their separation from the release sites, the junctions can be divided into 'close' and 'wide' junctions. Functionally, the 'close' and the 'wide' junctions can be distinguished by postjunctional potentials lasting ~1s and tens of seconds, respectively. Both synaptic and junctional communications are common between neurons; however, junctional transmission is the rule at many neuro-non-neural effectors.