Interaction of glutamate- and adenosine-induced decrease of acetylcholine quantal release at frog neuromuscular junction (original) (raw)
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Glutamate regulation of non-quantal release of acetylcholine in the rat neuromuscular junction
Journal of Neurochemistry, 2003
Glutamate, previously demonstrated to participate in regulation of the resting membrane potential in skeletal muscles, also regulates non-quantal acetylcholine (ACh) secretion from rat motor nerve endings. Non-quantal ACh secretion was estimated by the amplitude of endplate hyperpolarization (H-effect) following blockade of skeletal muscle post-synaptic nicotinic receptors by (+)-tubocurarine and cholinesterase by armin (diethoxy-p-nitrophenyl phosphate). Glutamate was shown to inhibit non-quantal release but not spontaneous and evoked quantal secretion of ACh. Glutamate-induced decrease of the H-effect was enhanced by glycine. Glycine alone also lowered the H-effect, probably due to potentiation of the effect of endogenous glutamate present in the synaptic cleft. Inhibition of N-methyl-D-aspartate (NMDA) receptors with (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10imine (MK801), DL-2-amino-5-phosphopentanoic acid (AP5) and 7-chlorokynurenic acid or the elimination of Ca 2+ from the bathing solution prevented the glutamate-induced decrease of the H-effect with or without glycine. Inhibition of muscle nitric oxide synthase by N G -nitro-L-arginine methyl ester (L-NAME), soluble guanylyl cyclase by 1H[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and binding and inactivation of extracellular nitric oxide (NO) by haemoglobin removed the action of glutamate and glycine on the H-effect. The results suggest that glutamate, acting on post-synaptic NMDA receptors to induce sarcoplasmic synthesis and release of NO, selectively inhibits non-quantal secretion of ACh from motor nerve terminals. Non-quantal ACh is known to modulate the resting membrane potential of muscle membrane via control of activity of chloride transport and a decrease in secretion of nonquantal transmitter following muscle denervation triggers the early post-denervation depolarization of muscle fibres. Abbreviations used: ACh, acetylcholine; AP5, DL-2-amino-5-phosphopentanoic acid; D-NAME, N G -nitro-D-arginine methyl ester; EPP, endplate potentials; L-NAME, N G -nitro-L-arginine methyl ester; mEPP, miniature endplate potentials; MK801, (+)-5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine; NO, nitric oxide; ODQ, 1H[1,2,4] oxadiazolo[4,3-a]quinoxalin-1-one.
Neuroscience and behavioral physiology
Experiments on rat diaphragm muscles showed that glutamate (10 microM-1 mM) had no effect on the mean frequency, interspike intervals, and amplitude-time characteristics of miniature endplate potentials, but had a suppressive action on non-quantum secretion (the intensity of which was assessed in terms of the H effect). The effect of glutamate was markedly concentration-dependent and was completely overcome by blockade of NMDA receptors, inhibition of NO synthase, and by binding of NO molecules in the extracellular space by hemoglobin. It is suggested that glutamate can modulate the non-quantum release of acetylcholine, initiating the synthesis of NO molecules in muscle fibers via activation of NMDA receptors followed by the retrograde action of NO on nerve terminals.
Journal of Neurochemistry, 2007
Nitric oxide (NO), previously demonstrated to participate in the regulation of the resting membrane potential in skeletal muscles via muscarinic receptors, also regulates nonquantal acetylcholine (ACh) secretion from rat motor nerve endings. Non-quantal ACh release was estimated by the amplitude of endplate hyperpolarization (H-effect) following a blockade of skeletal muscle post-synaptic nicotinic receptors by (+)-tubocurarine. The muscarinic agonists oxotremorine and muscarine lowered the H-effect and the M1 antagonist pirenzepine prevented this effect occurring at all. Another muscarinic agonist arecaidine but-2-ynyl ester tosylate (ABET), which is more selective for M2 receptors than for M1 receptors and 1,1-dimethyl-4-diphenylacetoxypiperidinium (DAMP), a specific antagonist of M3 cholinergic receptors had no significant effect on the H-effect. The oxotremorine-induced decrease in the H-effect was calcium and calmodulin-dependent. The decrease was negated when either NO synthase was inhibited by N G -nitro-Larginine methyl ester or soluble guanylyl cyclase was inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one. The target of muscle-derived NO is apparently nerve terminal guanylyl cyclase, because exogenous hemoglobin, acting as an NO scavenger, prevented the oxotremorine-induced drop in the H-effect. These results suggest that oxotremorine (and probably also non-quantal ACh) selectively inhibit the non-quantal secretion of ACh from motor nerve terminals acting on post-synaptic M1 receptors coupled to Ca 2+ channels in the sarcolemma to induce sarcoplasmic Ca 2+dependent synthesis and the release of NO. It seems that a substantial part of the H-effect can be physiologically regulated by this negative feedback loop, i.e., by NO from muscle fiber; there is apparently also Ca 2+ -and calmodulindependent regulation of ACh non-quantal release in the nerve terminal itself, as calmidazolium inhibition of the calmodulin led to a doubling of the resting H-effect.
On the type of receptor involved in the inhibitory action of adenosine at the neuromuscular junction
British Journal of Pharmacology, 1985
The effects of adenosine and adenosine analogues (1‐N6‐phenylisopropyladenosine (1‐PIA), d‐N6‐phenylisopropyladenosine (d‐PIA), N6‐cyclohexyladenosine (CHA), N6‐methyladenosine, 5′‐N‐ethyl‐carboxamide adenosine (NECA) and 2‐chloroadenosine) on evoked endplate potentials (e.p.ps) and on twitch tension were investigated in innervated sartorius muscles of the frog. Adenosine and its analogues decreased, in a concentration‐dependent manner, the amplitude of both the e.p.ps and the twitch responses evoked by indirect stimulation. The order of potencies in decreasing twitch tension was: 1‐PIA, CHA, NECA > 2‐chloroadenosine > d‐PIA > n6‐methyladenosine, adenosine. 1‐PIA was about ten fold more potent than d‐PIA. None of the adenosine analogues tested affected the twitch responses of directly stimulated tubocurarine‐paralyzed muscles. In concentrations that did not modify neuromuscular transmission, theophylline and 8‐phenylth‐eophylline (8‐PT) but not isobutylmethylxanthine (IBMX)...
British Journal of Pharmacology, 2004
At the mouse neuromuscular junction, adenosine (AD) and the A 1 agonist 2-chloro-N 6cyclopentyl-adenosine (CCPA) induce presynaptic inhibition of spontaneous acetylcholine (ACh) release by activation of A 1 AD receptors through a mechanism that is still unknown. To evaluate whether the inhibition is mediated by modulation of the voltage-dependent calcium channels (VDCCs) associated with tonic secretion (L-and N-type VDCCs), we measured the miniature endplate potential (mepp) frequency in mouse diaphragm muscles. 2 Blockade of VDCCs by Cd 2 þ prevented the effect of the CCPA. Nitrendipine (an L-type VDCC antagonist) but not o-conotoxin GVIA (an N-type VDCC antagonist) blocked the action of CCPA, suggesting that the decrease in spontaneous mepp frequency by CCPA is associated with an action on L-type VDCCs only. 3 As A 1 receptors are coupled to a G i/o protein, we investigated whether the inhibition of PKA or the activation of PKC is involved in the presynaptic inhibition mechanism. Neither N-(2[p-bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide (H-89, a PKA inhibitor), nor 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine (H-7, a PKC antagonist), nor phorbol 12-myristate 13-acetate (PHA, a PKC activator) modified CCPA-induced presynaptic inhibition, suggesting that these second messenger pathways are not involved. 4 The effect of CCPA was eliminated by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1naphthalenesulfonamide hydrochloride (W-7) and by ethylene glycol-bis(b-aminoethyl ether)-N,N,N 0 ,N 0-tetraacetic acid-acetoxymethyl ester e6TD-BM, which suggests that the action of CCPA to modulate L-type VDCCs may involve Ca 2 þ-calmodulin. 5 To investigate the action of CCPA on diverse degrees of nerve terminal depolarization, we studied its effect at different external K þ concentrations. The effect of CCPA on ACh secretion evoked by 10 mM K þ was prevented by the P/Q-type VDCC antagonist o-agatoxin IVA. 6 CCPA failed to inhibit the increases in mepp frequency evoked by 15 and 20 mM K þ. We demonstrated that, at high K þ concentrations, endogenous AD occupies A1 receptors, impairing the action of CCPA, since incubation with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, an A 1 receptor antagonist) and adenosine deaminase (ADA), which degrades AD into the inactive metabolite inosine, increased mepp frequency compared with that obtained in 15 and 20 mM K þ in the absence of the drugs. Moreover, CCPA was able to induce presynaptic inhibition in the presence of ADA. It is concluded that, at high K þ concentrations, the activation of A 1 receptors by endogenous AD prevents excessive neurotransmitter release.
European Journal of Neuroscience, 2013
Acetylcholinesterase (AChE) is an enzyme that hydrolyses the neurotransmitter acetylcholine, thereby limiting spillover and duration of action. This study demonstrates the existence of an endogenous mechanism for the regulation of synaptic AChE activity. At the rat extensor digitorum longus neuromuscular junction, activation of N-methyl-D-aspartate (NMDA) receptors by combined application of glutamate and glycine led to enhancement of nitric oxide (NO) production, resulting in partial AChE inhibition. Partial AChE inhibition was measured using increases in miniature endplate current amplitude. AChE inhibition by paraoxon, inactivation of NO synthase by N x -nitro-L-arginine methyl ester, and NMDA receptor blockade by DL-2-amino-5-phosphopentanoic acid prevented the increase in miniature endplate current amplitude caused by amino acids. High-frequency (10 Hz) motor nerve stimulation in a glycine-containing bathing solution also resulted in an increase in the amplitude of miniature endplate currents recorded during the interstimulus intervals. Pretreatment with an NO synthase inhibitor and NMDA receptor blockade fully eliminated this effect. This suggests that endogenous glutamate, released into the synaptic cleft as a co-mediator of acetylcholine, is capable of triggering the NMDA receptor/NO synthase-mediated pathway that modulates synaptic AChE activity. Therefore, in addition to well-established modes of synaptic plasticity (e.g. changes in the effectiveness of neurotransmitter release and/or the sensitivity of the postsynaptic membrane), another mechanism exists based on the prompt regulation of AChE activity.
The effects of exogenous nitric oxide on the function of neuromuscular synapses
2002
Extracellular recording experiments using neuromuscular skin/chest muscle preparations from lake frogs were performed at low extracellular Ca 2+ ion concentrations to study the effect of L-arginine (the substrate for nitric oxide synthesis) and N G -nitro-L-arginine methyl ester (a blocker of NO synthase) on the parameters of evoked transmitter secretion and ion currents in motor nerve endings. L-arginine at a concentration of 100 µM decreased the amplitude of endplate currents as well as their quantum composition, and also increased the amplitude of the third phase of the evoked nerve ending response, which reflects the kinetics of potassium influx currents. N G -nitro-L-arginine methyl ester at a condition of 100 µM led to increases in the amplitude and quantum composition of endplate currents and decreased the amplitude of the third phase of the evoked nerve ending response. It is suggested that endogenous nitric oxide is produced in frog neuromuscular synapses, which in normal conditions suppresses transmitter secretion and modulates the function of potassium channels in the nerve ending.