A Comprehensive Review on Pesticide Residues in Human Urine.

Numerous studies worldwide have evaluated pesticide residues detected in urine. This review serves as a contribution to this field by presenting an overview of scientific research studies published from 2001 to 2023, including details of study characteristics and research scope. Encompassing 72 papers, the review further delves into addressing key challenges in study design and method used such as sampling and analytical approaches, results adjustments, risk assessment, estimations, and results evaluation. The review explores urinary concentrations and detection frequency of metabolites of organophosphates and pyrethroids, as well as herbicides such as 2,4-D and glyphosate and their metabolites, across various studies. The association of the results with demographic and lifestyle variables were explored. While farmers generally have higher pesticide exposure, adopting organic farming practices can reduce the levels of pesticides detected in their urine. Residence close to agricultural areas has shown high exposure in some cases. Dietary exposure is especially high among people adopting a conventionally grown plant-rich dietary pattern. A higher detection level and frequency of detection are generally found in females and children compared to males. The implications of transitioning to organic and sustainable plant-rich diets for reducing pesticide exposure and potential health benefits for both adults and children require further investigation.

Assessing the performance of various sorbents in micro-solid phase extraction cartridges for pesticide residue analysis in feed.

Newly designed micro-solid phase extraction cartridges are now available, reflecting the increasing shift towards laboratory automation, especially in the clean-up step for the analysis of pesticide residues in food and feed. In the present study, the introduction of different sorbents on the newly designed PAL µSPE CTC cartridges was investigated for the removal of matrix interferents and the recovery of pesticides. Eight cartridges containing different sorbent combinations and different amounts were used including EMR-lipid (not activated), Z-sep, chitin, C18, PSA, and GCB. The evaluation of co-extractive removal for each cartridge showed that the optimal choice for removing fatty acids was the cartridges containing PSA and Z-sep as clean-up sorbents. However, the presence of C18 and EMR-lipid was still required for the removal of sterols and tocopherols. Two grams of sample, fish feed (FF) and rapeseed cake (RSC) were extracted using QuEChERS citrate buffer, followed by a freeze-out step. The recoveries and repeatability of QuEChERS using µ-SPE clean-up were evaluated for 216 pesticide residues (112 compounds analyzed by GC-MS/MS and 143 compounds by LC-MS/MS, from which 39 compounds were analyzed using both techniques). The best results, with recovery between 70 and 120% and RSD <20%, were achieved when FF samples were cleaned-up with 15 mg EMR-lipid and 20 mg MgSO4. This was achieved for 94% of GC-amenable compounds and 86% of LC-amenable compounds. In the case of RSC, the best results were seen when samples were cleaned-up with the cartridge containing only 20 mg Z-sep and 20 mg MgSO4. This was achieved for 88% of GC-amenable compounds and 90% of LC-amenable compounds. Although these cartridges yielded optimal results in terms of recovery, their use could require more instrument maintenance, especially for GC-MS/MS, due to the lower removal of co-extractives.

Results from the Danish monitoring programme on pesticide residues from the period 2012-2017 - frequencies and trends in detected pesticides.

In order to assess compliance with maximum residue levels in foods and evaluate the exposure of the Danish population to pesticides, a comprehensive monitoring programme was conducted. The work from 2012-2017 involved testing pesticide residues in fruits, vegetables, cereals, animal product and processed commodities. The sampling strategy, mainly based on exposure calculations and previous findings, involved the collection of 13,492 samples primarily from fresh conventional and organic produces on the Danish market. The origin of the samples varied, with 34% being of Danish origin and 67% originating from EU and non-EU countries. The results revealed that residues in conventionally grown produce were detected in 54% of the fruit and vegetable samples, and 30% of the cereal samples. Additionally, residues above the maximum residue limits were found in 1.8% of these samples, most frequently in fruits. As previous years, more residues were found in samples of foreign origin compared to samples of Danish origin. Compared to earlier findings more than 40 pesticides were detected for the first time and including boscalid, imidacloprid, thiacloprid, etofenprox, and spinosad, all detected more than 100 times. The data shows that detection of PFAS pesticides has increased dramatically, from 24 in 2006 to 412 in 2022.

Long-term cardiac computed tomography follow-up after left atrial appendage occlusion.

BACKGROUND: Left atrial appendage occlusion (LAAO) is performed increasingly, but long-term follow-up imaging data are lacking. AIMS: The aim of this study was to evaluate the safety and durability of the Amplatzer Amulet device >4 years after LAAO. METHODS: This was a prospective observational cohort study including 52 patients implanted with the Amplatzer Amulet device at Aarhus University Hospital, Denmark. A >4-year follow-up cardiac computed tomography (CT) scan after LAAO was performed and compared with the results from the 2-month and 12-month scans. The primary outcome was left atrial appendage (LAA) sealing based on distal LAA contrast patency and peridevice leakage (PDL), stratified into complete occlusion (grade 0 [G0]) and grade 1-3 leakage (G1-3), respectively. Secondary outcomes were low- and high-grade hypoattenuated thickening (HAT), device-related thrombosis (DRT) and device durability. RESULTS: The median (interquartile range [IQR]) follow-up time from LAAO to the latest CT scan was 5.8 years (4.5; 6.3). At 2-month (n=52), 12-month (n=27) and >4-year CT follow-ups (n=52), rates of both complete occlusion (33%, 37%, 35%) and G2 leaks (52%, 52%, 48%) remained stable. Rates of G1 leaks varied (14%, 4%, 6%) and G3 leaks rose (2%, 7%, 12%) from earliest to latest follow-up. The median left atrial (LA) volume increased from 127 mL (96; 176) to 144 mL (108; 182) and 147 mL (107; 193). No DRT was found. The structural device integrity was preserved. CONCLUSIONS: This study indicates a stable LAA sealing status throughout the follow-up period, emphasising the importance of the procedural result in avoiding PDL. Few patients displayed PDL progression, which might partly be related to LA remodelling with increasing volume. The long-term device durability appears excellent. Larger studies are warranted to confirm these findings.

Optimization of Postprocessing parameters for abdominal Forensic CT scans.

Aim: Postmortem Computed Tomography (PMCT) is gradually introduced at forensic institutes. Image reconstruction software can increase diagnostic potential in CT by increasing distinction between structures and reduction of artifacts. The aim of this study was to develop and evaluate novel image reconstruction parameters for postmortem conditions, to increase image quality and diagnostic potential of CT scans. Method: Twenty PMCT scans of deceased hereof two in severe decay were subjected to four reconstruction techniques: a standard reconstruction algorithm, the detail reconstruction algorithm and two novel algorithms based on the standard algorithm, but with different Hounsfield settings. Image quality was evaluated by visual grading analysis (VGA) by four forensic radiologist observers. Results: The VGA did not prove that any of the reconstruction techniques were superior to the others. For standard and detail, the two pre-defined reconstruction algorithms, VGA scores were indiscernible and were superior to the equally indiscernible Hounsfield reconstructions on parameters translated into Sharpness and Low Contrast Resolution. The two alternative Hounsfield settings were superior with respect to Noise and Artifacts/Beam Hardening. Conclusion: The study elucidates the possiblity for multiple reconstructions specialized for PMCT conditions, to accommodate the special conditions when working with the deceased. Despite the lack of clear improvements in the tested reconstructions, this study provides an insight into some of the possibilities of improving PMCT quality using reconstruction techniques.

Human P2X7 receptor variants Gly150Arg and Arg276His polymorphisms have differential effects on risk association and cellular functions in pancreatic cancer.

BACKGROUND: The purinergic P2X7 receptor (P2X7R) plays an important role in the crosstalk between pancreatic stellate cells (PSCs) and cancer cells, thus promoting progression of pancreatic ductal adenocarcinoma (PDAC). Single nucleotide polymorphisms (SNPs) in the P2X7R have been reported for several cancers, but have not been explored in PDAC. MATERIALS AND METHODS: Blood samples from PDAC patients and controls were genotyped for 11 non-synonymous SNPs in P2X7R and a risk analysis was performed. Relevant P2X7R-SNP GFP variants were expressed in PSCs and cancer cells and their function was assayed in the following tests. Responses in Ca2+ were studied with Fura-2 and dye uptake with YO-PRO-1. Cell migration was monitored by fluorescence microscopy. Released cytokines were measured with MSD assay. RESULTS: Risk analysis showed that two SNPs 474G>A and 853G>A (rs28360447, rs7958316), that lead to the Gly150Arg and Arg276His variants, had a significant but opposite risk association with PDAC development, protecting against and predisposing to the disease, respectively. In vitro experiments performed on cancer cells and PSCs expressing the Gly150Arg variant showed reduced intracellular Ca2+ response, fluorescent dye uptake, and cell migration, while the Arg276His variant reduced dye uptake but displayed WT-like Ca2+ responses. As predicted, P2X7R was involved in cytokine release (IL-6, IL-1ß, IL-8, TNF-α), but the P2X7R inhibitors displayed varied effects. CONCLUSION: In conclusion, we provide evidence for the P2X7R SNPs association with PDAC and propose that they could be considered as potential biomarkers.

The Needle Shield Size and Applied Force of Subcutaneous Autoinjectors Significantly Influence the Injection Depth.

BACKGROUND: This study examines how shield-triggered autoinjectors (AIs), for subcutaneous drug delivery, affect injection depth. It focuses on shield size and applied force, parameters that could potentially lead to inadvertent intramuscular (IM) injections due to tissue compression. METHOD: A blinded ex-vivo study was performed to assess the impact of shield size and applied force on injection depth. Shields of 15, 20, and 30 mm diameters and forces from 2 to 10 N were investigated. The study involved 55 injections in three Landrace, Yorkshire, and Duroc (LYD) pigs, with injection depths measured with computed tomography (CT). An in-vivo study, involving 20 injections in three LYD pigs, controlled the findings, using fluoroscopy (FS) videos for depth measurement. RESULTS: The CT study revealed that smaller shield sizes significantly increased injection depth. With a 15 mm diameter shield, 10 N applied force, and 5 mm needle protrusion, the injection depth exceeded the needle length by over 3 mm. Injection depth increased with higher applied forces until a plateau was reached around 8 N. Both applied force and size were significant factors for injection depth (analysis of variance [ANOVA], P < .05) in the CT study. The FS study confirmed the ex-vivo findings in an in-vivo setting. CONCLUSIONS: The study demonstrates that shield size has a greater impact on injection depth than the applied force. While conducted in porcine tissue, the study provides useful insights into the relative effects of shield size and applied force. Further investigations in humans are needed to confirm the predicted injection depths for AIs.

Fate of pesticide residues in beer and its by-products.

Sustainable beer production requires a comprehensive assessment of potential hazards such as pesticides in both the finished product and waste streams, as these streams can be used to create high-value by-products. This study presents the tracking of 13 fungicides (azoxystrobin, boscalid, epoxiconazole, fenpropidin, fenpropimorph, fluquiconazole, flutriafol, fluxapyroxad, kresoxym-methyl, spiroxamine, propiconazole, prothioconazole-desthio, and tebuconazole), two insecticides (chlorpyrifos-methyl and deltamethrin), one herbicide (glyphosate), and one growth regulator (mepiquat) through the beer brewing process. Field-treated rye, wheat, and barley samples containing pesticide residues were used as adjunct during brewing. Samples of the beer as well as the by-products (spent grain, spent hops, trub and spent yeast) were collected and extracted with a modified QuEChERS method for pesticide residues analysis using GC-MS/MS and LC-MS/MS. Results show that an average of 58% of pesticide residues are retrieved in the by-products with the highest fraction (53%) recovered in the spent grain, 4% in trub, 1% in spent hops, no residues detected in spent yeast and 9% in the beer. This is consistent with these nonpolar pesticides tending to remain adsorbed to the spent grain during brewing. Glyphosate and mepiquat, the most polar pesticides included in this study, showed a different behavior, with the largest fraction (>80%) being retrieved in sweet wort and transferred to the beer. Processing factors were generated for each pesticide from the adjunct to the beer and to the four by-products.

New-onset atrial fibrillation in critically ill adult patients-an SSAI clinical practice guideline.

BACKGROUND: Acute or new-onset atrial fibrillation (NOAF) is the most common cardiac arrhythmia in critically ill adult patients, and observational data suggests that NOAF is associated to adverse outcomes. METHODS: We prepared this guideline according to the Grading of Recommendations Assessment, Development and Evaluation methodology. We posed the following clinical questions: (1) what is the better first-line pharmacological agent for the treatment of NOAF in critically ill adult patients?, (2) should we use direct current (DC) cardioversion in critically ill adult patients with NOAF and hemodynamic instability caused by atrial fibrillation?, (3) should we use anticoagulant therapy in critically ill adult patients with NOAF?, and (4) should critically ill adult patients with NOAF receive follow-up after discharge from hospital? We assessed patient-important outcomes, including mortality, thromboembolic events, and adverse events. Patients and relatives were part of the guideline panel. RESULTS: The quantity and quality of evidence on the management of NOAF in critically ill adults was very limited, and we did not identify any relevant direct or indirect evidence from randomized clinical trials for the prespecified PICO questions. We were able to propose one weak recommendation against routine use of therapeutic dose anticoagulant therapy, and one best practice statement for routine follow-up by a cardiologist after hospital discharge. We were not able to propose any recommendations on the better first-line pharmacological agent or whether to use DC cardioversion in critically ill patients with hemodynamic instability induced by NOAF. An electronic version of this guideline in layered and interactive format is available in MAGIC: https://app.magicapp.org/#/guideline/7197. CONCLUSIONS: The body of evidence on the management of NOAF in critically ill adults is very limited and not informed by direct evidence from randomized clinical trials. Practice variation appears considerable.

Biomechanical properties of the stomach: A comprehensive comparative analysis of human and porcine gastric tissue.

BACKGROUND: Stomach-related disorders impose medical challenges and are associated with significant social and economic costs. The field of biomechanics is promising for understanding tissue behavior and for development of medical treatments and surgical interventions. In gastroenterology, animal models are often used when studies on humans are not possible. Often large animal models with similar anatomical characteristics (size and shape) are preferred. However, it is uncertain if stomachs from humans and large animals have similar mechanical properties. The aim of the present study is to characterize and compare hyper- and viscoelastic properties of porcine and human gastric tissue using tension and radial compression tests. METHODS: Hyperelastic and viscoelastic properties were quantified from quasi-static ramp tests and stress relaxation tests. Tension in two directions and radial compression experiments were done on intact stomach wall samples as well as on separated mucosa and muscularis layer samples from porcine and human fundus, corpus and antrum. RESULTS AND CONCLUSIONS: Similar hyper- and viscoelastic constitutive models can be used to describe porcine and human gastric tissue. In total, 19 constitutive parameters were compared and results showed significant variations between species. For example, for intact circumferential samples from antrum, the stiffness (a) and relaxation (τ1) were greater for human samples than for porcine samples (p < 0.0001). The constitutive parameters were condition-, region- and layer-dependent and no distinct pattern hereof between species was found. This indicates that different parameters must be used to describe the specific situation. The present work provides insight into porcine and human gastric radial compressive and tensile hyper- and viscoelastic properties, strengthening the inter-species relation of the biomechanical properties. Constitutive relations were established that may aid development and translation of diagnostic or therapeutic devices with computational models.

Cumulative dietary risk assessment of pesticides in food for the Danish population for the period 2012-2017.

The cumulative chronic dietary exposure for the Danish population were assessed using Danish food monitoring data for the period 2012-2017 and Danish food consumption data for the consumer groups children (age 1-2, age 4-6 and age 7-14 years), adults age 15-75, high consumers and consumers eating Danish produced fruit and vegetables whenever possible. Levels below the Limit of Reporting (LOR) were set to ½ LOR with correction. For risk assessment of the cumulative chronic dietary exposure we used the Hazard Index (HI) method where the Hazard Quotient (HQ) was calculated for each pesticide and summed up to a HI. The HI was calculated to be below 1 for all consumer groups; i.e. 0.36 for children age 4-6 years and 0.13 for adults, indicating that the cumulative chronic dietary pesticide exposure is unlikely to constitute a health risk for Danish consumers, even for high consumers eating 600 g or more of fruit and vegetables each day. By eating Danish produced commodities whenever possible, the HI was reduced by a factor of one third for both children and adults. 25 different commodities contributed to about 90% of the HI and to 84% of the exposure.

P2X2 receptor subunit interfaces are missense variant hotspots, where mutations tend to increase apparent ATP affinity.

BACKGROUND AND PURPOSE: P2X receptors are trimeric ligand-gated ion channels that open a cation-selective pore in response to ATP binding to their large extracellular domain. The seven known P2X subtypes can assemble as homotrimeric or heterotrimeric complexes and contribute to numerous physiological functions, including nociception, inflammation and hearing. The overall structure of P2X receptors is well established, but little is known about the range and prevalence of human genetic variations and the functional implications of specific domains. EXPERIMENTAL APPROACH: Here, we examine the impact of P2X2 receptor inter-subunit interface missense variants identified in the human population or by structural predictions. We test both single and double mutants through electrophysiological and biochemical approaches. KEY RESULTS: We demonstrate that predicted extracellular domain inter-subunit interfaces display a higher-than-expected density of missense variations and that the majority of mutations that disrupt putative inter-subunit interactions result in channels with higher apparent ATP affinity. Lastly, we show that double mutants at the subunit interface show significant energetic coupling, especially if located in close proximity. CONCLUSION AND IMPLICATIONS: We provide the first structural mapping of the mutational distribution across the human population in a ligand-gated ion channel and show that the density of missense mutations is constrained between protein domains, indicating evolutionary selection at the domain level. Our data may indicate that, unlike other ligand-gated ion channels, P2X2 receptors have evolved an intrinsically high threshold for activation, possibly to allow for additional modulation or as a cellular protection mechanism against overstimulation.

Chlorate and perchlorate residues in food products on the Danish market.

Upon the European commission's request in 2013, Denmark initiated a survey of the levels of chlorate and perchlorate in agriculture products from the Danish market over a period of 4 years from 2014 to 2017. The results of the survey were used to guide decision making with a view to setting maximum levels for intra-Union trade in 2013 and reviewing and updating the levels from 2020. The results of the Danish survey and the employed analytical method are documented in this paper. In addition to the 89 domestic samples, 30 samples of foreign origin were analysed for chlorate and perchlorate, together with ten samples of baby food and seven samples of infant formula collected from the Danish market. Samples were extracted using the Quick Polar Pesticides extraction method (QuPPe) and analysed on a triple quadrupole LC-MS/MS system. The levels of both chlorate and perchlorate detected in samples originating from Denmark were lower than the current MRLs except for a single sample of lettuce. Moreover, the percentage of foreign samples that were positive for chlorate and perchlorate residues was higher than the percentage of domestic samples. The reason for the generally low levels and low frequency of chlorate and perchlorate in Danish products is most likely linked to the fact that the water supply in Denmark is 100% unchlorinated ground water. The present study shows that residues of perchlorate and chlorate are found in Danish food products at a relatively low frequency and that the levels found are below the EU's MRLs implemented in 2020.

Oral delivery of systemic monoclonal antibodies, peptides and small molecules using gastric auto-injectors.

Oral administration provides a simple and non-invasive approach for drug delivery. However, due to poor absorption and swift enzymatic degradation in the gastrointestinal tract, a wide range of molecules must be parenterally injected to attain required doses and pharmacokinetics. Here we present an orally dosed liquid auto-injector capable of delivering up to 4-mg doses of a bioavailable drug with the rapid pharmacokinetics of an injection, reaching an absolute bioavailability of up to 80% and a maximum plasma drug concentration within 30 min after dosing. This approach improves dosing efficiencies and pharmacokinetics an order of magnitude over our previously designed injector capsules and up to two orders of magnitude over clinically available and preclinical chemical permeation enhancement technologies. We administered the capsules to swine for delivery of clinically relevant doses of four commonly injected medications, including adalimumab, a GLP-1 analog, recombinant human insulin and epinephrine. These multi-day dosing experiments and oral administration in awake animal models support the translational potential of the system.

Evaluation of the automated micro-solid phase extraction clean-up system for the analysis of pesticide residues in cereals by gas chromatography-Orbitrap mass spectrometry.

Food analysis is a tremendously broad field that is constantly evolving. New methods have emerged to increase productivity, such as modern miniaturized and robotic analytical techniques. In this paper, a micro-solid-phase extraction system (µ-SPE) for clean-up was combined with a robotic autosampler to yield ready-to-analyze extracts. The system was evaluated for its applicability in routine laboratories. The new, automated, high-throughput µ-SPE clean-up method was applied to acetonitrile extracts and was developed for the analysis of pesticide residues in cereals by gas chromatography-Orbitrap mass spectrometry (GC-Orbitrap-MS). The µ-SPE clean-up efficiency was demonstrated in the removal of matrix-interfering components and in the recovery of pesticides. The sorbent bed mixture consisted of magnesium sulfate, primary-secondary amine, C18, and CarbonX, and effectively retained matrix components without loss of target analytes. Analysis of five types of cereals (barley, oat, rice, rye, and wheat) by GC-Orbitrap-MS showed that the method removed more than 70% of matrix components. The clean-up method was validated for 170 pesticides in rye, 159 pesticides in wheat, 142 pesticides in barley, 130 pesticides in oat, and 127 pesticides in rice. Spike recovery values were 70-120% for all pesticides and the repeatability, calculated as the relative standard deviation, was less than 20%. The limits of quantitation achieved were 0.005 mg kg-1 for almost all analytes, ensuring compliance with the maximum residue limits.

Crosslinking glutamate receptor ion channels.

Combining crosslinking strategies with electrophysiology, biochemistry, and structural in silico analysis is a powerful tool to study transient movements of ion channels during gating. This chapter describes crosslinking in living cells using cysteine and photoactive unnatural amino acids (UAAs) that we have used on glutamate receptor ion channels. Here, we share the protocol for building a perfusion tool to enable rapid chemical modification of glutamate-gated AMPA receptors, optimized for their fast activation. This system can be used to perform state-dependent crosslinking in receptors modified by cysteines or UAA incorporation on the millisecond timescale. Introducing UAAs results in receptors with lower expression levels relative to the introduction of cysteine residues. Reduced expression is principally a challenge for biochemical studies, and we share here our approach to capture the light driven oligomerization of AMPA receptors containing UAA crosslinkers. Finally, we describe strategies for computational analysis to make sense of the crosslinking results in terms of structure and function.

Development of a new generic extraction method for the analysis of pesticides, mycotoxins, and polycyclic aromatic hydrocarbons in representative animal feed and food samples.

Various generic extraction methods have been used to determine pesticide residues, mycotoxins, and polycyclic aromatic hydrocarbons (PAHs) in food and animal feed to ensure consumer safety. However, these methods cannot extract all relevant compounds at an acceptable rate of recovery. This study presents a new extraction method. This new method facilitated the identification of 231 compounds, including 196 pesticides, 11 mycotoxins, and 24 PAHs over a broad range of polarities. These compounds were identified in various sample matrices, including those that are lipid-rich. The processed sample is first extracted with water, acetonitrile, formic acid, and heptane. The addition of ammonium formate results in separation into three phases and enables analysis of the aqueous phase. Solid-phase extraction clean-up procedures were performed as necessary followed by analysis by liquid or gas chromatography and mass spectrometry. Analyte recoveries were typically in the range of 70 - 120% with relative standard deviations below 20%.

Processing factors of pesticide residues in biscuits and their relation to the physicochemical properties of pesticides.

Agricultural commodities are generally consumed as processed food. Therefore, it is indispensable to assess pesticide residues in processed products rather than only in the raw agricultural commodity, in order to approach a more realistic scenario of dietary exposure. Processing factors are important tools for dietary exposure risk assessments. In this study, processing factors for the baking process were derived for 41 pesticides in cereal bran-based biscuits. The raw materials used consisted of wheat, rye, oat, and barley grains with incurred pesticides, which originally was produced for test material for European Union Proficiency Tests. Information on physicochemical properties of pesticides was collected for understanding the fate of pesticides during the baking process. Average processing factors varied between 0.67 and 1.6. Most pesticide residues exhibited a reduction of pesticide residues of less than 24%, which correspond to a processing factor (PF) range between 1 and 0.76, showing resistance to the baking process. However, for polar compounds such as carbendazim and volatile compounds (chlorpyrifos-methyl, malathion, and pirimiphos-methyl) larger reduction rates were observed, up to 33% (PF: 0.67). In general, a prolonged baking time did not significantly affect the PF, because the main degradation process takes place within the first 6 min. However, this was not the case for the highly volatile compounds, highly polar compounds, and compounds of low degradation temperature. These latter were significantly reduced with prolonged baking time, resulting in a reduction rate of up to 95%, which means an almost complete elimination.

Gating modules of the AMPA receptor pore domain revealed by unnatural amino acid mutagenesis.

Ionotropic glutamate receptors (iGluRs) are responsible for fast synaptic transmission throughout the vertebrate nervous system. Conformational changes of the transmembrane domain (TMD) underlying ion channel activation and desensitization remain poorly understood. Here, we explored the dynamics of the TMD of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type iGluRs using genetically encoded unnatural amino acid (UAA) photocross-linkers, p-benzoyl-l-phenylalanine (BzF) and p-azido-l-phenylalanine (AzF). We introduced these UAAs at sites throughout the TMD of the GluA2 receptor and characterized the mutants in patch-clamp recordings, exposing them to glutamate and ultraviolet (UV) light. This approach revealed a range of optical effects on the activity of mutant receptors. We found evidence for an interaction between the Pre-M1 and the M4 TMD helix during desensitization. Photoactivation at F579AzF, a residue behind the selectivity filter in the M2 segment, had extraordinarily broad effects on gating and desensitization. This observation suggests coupling to other parts of the receptor and like in other tetrameric ion channels, selectivity filter gating.

Controlling Ca2+ Permeable α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptors with Photochromic Ion Channel Blockers.

Ionotropic glutamate receptors (iGluRs) play a critical role in normal brain function and neurodegenerative diseases. Development of light-dependent compounds would enable studies of iGluRs within intact mammalian neural tissue, as light is noninvasive and can be applied with high spatiotemporal precision. Here we develop a potent photochromic antagonist that selectively targets the Ca2+ permeable AMPA-type of iGuRs, thus providing an important tool to study the contribution of AMPA-type iGluRs on neuronal activity.