Search

Effects of gamma-aminobutyric acid (GABA) and some selective GABAergic ligands on the quantal acetylcholine (ACh) release in the frog neuromuscular contacts were investigated using combination of microelectrode technique with fluorescent and immunohistochemical assays. Significant attenuation of ACh release was observed in the presence of GABA as well as selective GABA A and GABA B receptor agonists. Neither GABA A nor GABA B antagonists abolished to full extent this effect of GABA. Fluorescent assay allowed to detect the GABA-induced opening of K + channels, which was inhibited by XE-991, a selective antagonist of K v 7 type. Electrophysiological recordings of endplate potentials in the presence of XE-991 confirmed the contribution of K v 7 type potassium channels to the effects of GABA on ACh release that was not associated with GABA A and GABA B receptors activation. Note that XE-991 effectively precluded the action of retigabine, neuronal K v 7 channel opener, on ACh release. Immunohistochemical assay revealed that frog mature skeletal muscle fibers contain a significant amount of GABA, and substantial amount of GABA can be released in the extracellular space at the muscle contractions induced by prolonged high-frequency nerve stimulation. Besides, some binding sites for exogenous GABA were detected on the plasma membranes. It is concluded that GABA, in addition to affecting GABA A and GABA B receptors, can directly activate K v 7 channels, thereby negatively modulating the evoked ACh release. Endogenous GABA may serve as a retrograde regulator of neurotransmitter exocytosis., Competing Interests: Declarations Ethics Approval The experimental protocol met the requirements of the EU Directive 2010/63/EU and was approved by the Local Ethical Committee of Kazan Federal Scientific Centre (Protocol #3/February 28, 2023) as well as by the Local Ethical Committee of Kazan State Medical University (Protocol #5/May 27, 2014). The current study was conducted in compliance with the NIH Guide for the Care and Use of Laboratory Animals. Consent for Publication Not applicable. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. All authors consent to publish the article., (© 2024. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Mathematical modeling was applied to study the dependence of miniature endplate current (MEPC) amplitude and temporal parameters on the values of the rate constants of acetylcholine binding to receptors (k+) when cholinesterase was either active or inactive. The simulation was performed under two different sets of parameters describing acetylcholine receptor activation--one with high and another with low probability (Pohigh and Polow) of receptor transition into the open state after double ligand binding. The dependence of model MEPC amplitudes, rise times, and decay times on k+ differs for set Polow and set Pohigh. The main outcome is that for set Pohigh, the rise time is significantly longer at low values of k+ because of the prolongation of ACh diffusion time to the receptor. For the set Polow, the rise time is shorter at low values of k+, which can be explained by the small probability of AChR forward isomerization after ACh binding and faster MEPC's peak formation.