title: Acetylcholine-Induced Inhibition of Presynaptic Calcium Signals and Transmitter Release in the Frog Neuromuscular Junction.
abstract: Acetylcholine (ACh), released from axonal terminals of motor neurons in neuromuscular junctions regulates the efficacy of neurotransmission through activation of presynaptic nicotinic and muscarinic autoreceptors. Receptor-mediated presynaptic regulation could reflect either direct action on exocytotic machinery or modulation of Ca2+entry and resulting intra-terminal Ca2+dynamics. We have measured free intra-terminal cytosolic Ca2+([Ca2+]i) using Oregon-Green 488 microfluorimetry, in parallel with voltage-clamp recordings of spontaneous (mEPC) and evoked (EPC) postsynaptic currents in post-junctional skeletal muscle fiber. Activation of presynaptic muscarinic and nicotinic receptors with exogenous acetylcholine and its non-hydrolized analog carbachol reduced amplitude of the intra-terminal [Ca2+]itransients and decreased quantal content (calculated by dividing the area under EPC curve by the area under mEPC curve). Pharmacological analysis revealed the role of muscarinic receptors of M2subtype as well as d-tubocurarine-sensitive nicotinic receptor in presynaptic modulation of [Ca2+]itransients. Modulation of synaptic transmission efficacy by ACh receptors was completely eliminated by pharmacological inhibition of N-type Ca2+channels. We conclude that ACh receptor-mediated reduction of Ca2+entry into the nerve terminal through N-type Ca2+channels represents one of possible mechanism of presynaptic modulation in frog neuromuscular junction.
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia; Institute of Applied Electrodynamics, Photonics and Living Systems, A.N. Tupolev Kazan National Research Technical UniversityKazan, Russia.
authors.forename: Eduard
authors.initials: E
authors.lastname: Khaziev
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia; Institute of Applied Electrodynamics, Photonics and Living Systems, A.N. Tupolev Kazan National Research Technical UniversityKazan, Russia.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Samigullin
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia.
authors.forename: Nikita
authors.initials: N
authors.lastname: Zhilyakov
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of Sciences Kazan, Russia.
authors.forename: Nijaz
authors.initials: N
authors.lastname: Fatikhov
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia.
authors.forename: Ellya
authors.initials: E
authors.lastname: Bukharaeva
authors.affiliation: Faculty of Life Sciences, University of Manchester Manchester, UK.
authors.forename: Alexei
authors.initials: A
authors.lastname: Verkhratsky
authors.affiliation: Laboratory of Biophysics of Synaptic Processes, Kazan Institute of Biochemistry and Biophysics, Kazan Scientific Center of the Russian Academy of SciencesKazan, Russia; Open Laboratory of Neuropharmacology, Kazan (Volga Region) Federal UniversityKazan, Russia; Department of Biophysics, Kazan State Medical UniversityKazan, Russia.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Nikolsky
keywords: N-type Ca channels; calcium transient; muscarinic receptors; neuromuscular synapse; nicotinic receptors; presynaptic acetylcholine receptors; quantum secretion of acetylcholine