Independent release of supranormal acetylcholine quanta at the rat neuromuscular junction

This electrophysiological study deals with the occurrence and with the mode of release of unusually large miniature end-plate potentials at the rat neuromuscular junction during physiological conditions. A specific limit for the normal miniature end-plate potential amplitude at each cell studied was determined after fitting the observed frequency-amplitude histogram to a Gaussian distribution. The relative abundance of giant miniature end-plate potentials was 4.15% at room temperature. The occurrence of giant miniature end-plate potentials was temperature dependent. The percentage of giant miniature end-plate potentials was 5.8% and 0.61% at 35 degrees C and at 16 degrees C, respectively. The amplitude-independence of the intervals between miniature end-plate potentials was demonstrated at room temperature as well as at 35 degrees C and at 16 degrees C. The results of this study show that giant miniature end-plate potentials are produced by acetylcholine packets which are released independently and that they are not a consequence of the synchronous release of several normal-sized quanta. Moreover, the results indicate that during physiological conditions a minor but regular proportion of the spontaneous release of acetylcholine is made up of larger packets, which produce miniature end-plate potentials of supranormal amplitude.     

A new type of transmitter release at the neuromuscular junction

Examination of spontaneous miniature endplate potentials (MEPPs) in murine skeletal muscle has revealed that in conditions such as botulinum poisoning, during nerve terminal regeneration or in the presence of the drug 4-aminoquinoline, two types of acetylcholine release are responsible for the MEPPs. In addition to the MEPPs which correspond to the quantal component of a nerve impulse-evoked endplate potential a second type of acetylcholine release occurs. The latter type of transmitter release gives rise to MEPPs with a more prolonged time-to-peak and frequently a larger than normal amplitude. It is unaffected by nerve terminal depolarization and transmembrane Ca2+ fluxes. The relationship between MEPP frequency and temperature has a Q10 of about 12 compared to 2-3 for normal MEPPs. In botulinum-poisoned muscles this secretory type of transmitter release dominates, being exclusively present in muscles where nerve stimulation fails to release transmitter. In normal muscle such a release is induced by 4-aminoquinoline which may cause up to 45% of all the spontaneous MEPPs to be of that kind. It is suggested that the described spontaneous secretion of acetylcholine serves in inductory and neurotrophic function.     

Ultrastructural and physiological effects of the ionophore A23187 at identified frog neuromuscular junctions

The physiological and morphological effects of the calcium ionophore A23187 (calimycin) at the frog neuromuscular junction in vitro were examined. Miniature endplate potentials were recorded intracellularly during exposure to the ionophore. Preparations fixed 15 or 30 min after adding the drug to the incubating medium, which exhibited a greatly increased miniature endplate potential frequency, showed no obvious morphological differences when compared to controls with regard to synaptic vesicle number or distribution of vesicles within the terminal. However, after 45-60 min of exposure to the ionophore, when miniature endplate potential frequency had declined almost to zero, most of the nerve endings appeared devoid of synaptic vesicles and other organelles while the plasma membrane was intact. It is suggested that the apparent depletion of vesicles from the terminal induced by the calcium ionophore is a consequence of irreversible changes at the terminal.     

Spontaneous potentials and fine structure of identified frog denervated neuromuscular junctions

Morphological changes at the neuromuscular junction of the frog during nerve degeneration were correlated with the occurrence of either nerve or Schwann cell-induced miniature endplate potentials in identified edge muscle cells that were subsequently examined in the electron microscope. The initial stages of nerve deterioration produced showers of nerve-induced miniature endplate potentials but showed no apparent change in the vesicle population in nerve terminals. When the miniature endplate potentials ceased, the nerve ending appeared dense and exhibited clumped vesicles, swollen and disrupted mitochondria and membrane whorls. Nerve death was followed by movement and growth of the Schwann cell into the space previously occupied by the nerve terminal. The Schwann cell-muscle junctions were initially silent and no obvious morphological change accompanied the generation of miniature endplate potentials. Schwann cell-induced miniature endplate potentials had frequencies of 10–100/min which were comparable to the frequencies of nerve-induced miniature endplate potentials from similar sized neuromuscular junctions. Some histograms of Schwann cell-induced miniature endplate potentials showed a peak demonstrating a mean quantal size.Only a few vesicles were found in Schwann cells, including the high frequency junctions, so the morphological storage site for the production of miniature endplate potentials is not obvious. The frequencies of miniature endplate potentials evoked by Schwann cells were usually altered in the opposite direction to those evoked by nerves following various challenges, suggesting that the release mechanism for acetylcholine is quite different.     

A study on early post-denervation changes of non-quantal and quantal acetylcholine release in the rat diaphragm

The d-tubocurarine (dTC) induced hyperpolarization of antiesterase-treated muscles at the endplate zone, miniature endplate potentials (mepps), resting membrane potentials (RMPs) and the input resistances of single muscle fibres (R_in) were measured in rat diaphragm at various times after denervation. The dTC-induced hyperpolarization decreased in two phases: 2 h after denervation it decreased transiently to 25%, after 4 h it had partially recovered to 60% and from 6 h it progressively decreased up to 12 h after which time it changed to depolarization. The initial fall and recovery were also present in muscles from sham-operated animals. The frequency of mepps decreased by 25% and the amplitude diminished by 10% within the first 2–4 h. After 10 h the frequency had decreased by 35% and the amplitude by 65%. After 12 h no mepps were present. The RMP was not significantly changed during the first 16 h after denervation. From 16 to 24 h the membrane became depolarized at a rate of about 1 mV/h. The input resistance of a single muscle fibre was constant for 12 h after denervation and from 12 to 24 h it increased by 25%. It is concluded that the early decrease in the dTC-induced hyperpolarization is probably due to the desensitization of acetylcholine (ACh) receptors caused by stress-activated non-quantal ACh release. The later decrease of dTC-hyperpolarization reflects a fall in the non-quantal ACh release. The depolarization of the resting membrane after denervation is related to the decrease in passive membrane permeability which is a secondary consequence of transmission failure. The present results do not distinguish between non-quantally released and quantally released ACh as possible trophic agents, since both types of release disappear at the same time.     

Muscle reinnervation--I. Restoration of transmitter release mechanisms

Following sciatic nerve crush the restoration of neuromuscular transmission in the extensor digitorum longus muscle of rat proceeds in a well defined manner: (a) as soon as the nerve-muscle contact is reformed, a subthreshold end-plate potential is recorded; no 'non-transmitting stage' is observed; (b) 24 hours later muscle action potentials are induced by nerve stimulation; (c) miniature end-plate potentials are absent or very rare at the newly reinnervated end-plates; their frequency returns to normal in about 4 weeks; (d) the frequency is also very much reduced in 30 mM K+ and hypertonic solutions and recovers slowly, in 4 and 5 weeks, respectively, while black widow spider venom is from the beginning as powerful as in normal neuromuscular junctions; (e) at the early stages of reinnervation the Ca2+-dependent release mechanisms are much stronger than control cases, while the Ca2+-independent mechanisms are weaker and recover in 5 weeks. The gradual reassembly and restoration of neurotransmitter release mechanisms of the extensor digitorum longus nerve terminal indicate the complexity of pre-synaptic ending organization.     

Effect of Mg2+ on non-quantal acetylcholine release at the mouse neuromuscular junction

The effects of extracellular concentrations of Mg2+ on the non-quantal release of acetylcholine (ACh) from nerve terminals was studied by extra- and intracellular electrophysiological methods. Anticholinesterase-treated mouse diaphragms were used in vitro. In the presence of Ca2+, the non-quantal release was maximal in the absence of Mg2+ and was inhibited by 3 mmol/l Mg2+. The inhibitory effect of Mg2+ was antagonized by ouabain and was absent in Ca2+-free (EGTA) solutions. The non-quantal release of ACh was found to be more sensitive to inhibition by Mg2+ than the quantal one which was measured as the amplitude of miniature endplate currents.     

Effect of lanthanum ions on the amplitude distributions of miniature endplate potentials and on synaptic vesicles in frog neuromuscular junctions

Miniature endplate potential (MEPP) amplitude distributions, MEPP frequencies and percentages of small MEPPs were determined as well as synaptic vesicle diameters and numbers in the frog neuromuscular junction during La3+ treatment. MEPP frequencies initially increased by two orders of magnitude and then fell to very low values. La3+ treatment had an initial postsynaptic effect making the MEPPs larger. Prolonged treatment had a variable effect on MEPP amplitudes. There were considerable variations in MEPP frequencies in adjacent junctions so single junctions on edge muscle fibers were recorded for the duration of many experiments and later identified in the electron microscope. Therefore, the physiological and morphological conditions of a given identified junction could be compared. There was a loss of synaptic vesicles and no change in mean diameter during depletion. During high MEPP frequencies infoldings occurred on the axolemma and these disappeared when MEPP frequencies decreased towards the end of the La3+ treatment. After 3-4 h of La3+ treatment, the overall frequency of MEPPs dropped and many were composed of a small class of MEPPs. It is suggested that the morphological correlate of small MEPPs, as well as the classical bell-MEPPs is likely to be synaptic vesicles.     

The effect of temperature on the amplitude distributions of miniature endplate potentials in the mouse diaphragm

The effect of temperature (11 to 45°C) on miniature endplate potential (MEPP) distributions was examined at the mouse diaphragm. MEPP distributions were composed of two populations ('skew-MEPPS' and ‘bell-MEPPs’) and the mode of the skew-MEPP population (subminiature endplate potential, sub-MEPP) had an amplitude equal to 1/10 to 1/15 the mean of the normally distributed bell-MEPP class. The overall MEPP frequency increased with a Q₁₀ of 2.2 between 11 and 30°C, and an Arrhenius plot indicated two temperature-sensitive reactions between 11 and 45°C. Below 30°C, the activation energy was 10.4 kcal/mole K and between 30 and 45°C the activation energy was 38.7 kcal/ mole K. The proportion of skew-MEPPs between different fibers was independent of the overall MEPP frequency and varied between 1% and 31% at temperatures of 11–34°C. However, as the temperature was lowered below 24°C, the decrease in frequency of skew-MEPPs was more than that of bell-MEPPs. Conversely, an increase in temperature from 24 to 34°C increased the bell-MEPP frequency but either reduced or had little effect on the frequency of skew-MEPPs. Following heat challenges (T > 40°C), MEPP distributions contained a large percentage of skew-MEPPs and the profile of the MEPP distribution became uniform. Before complete cessation of spontaneous activity with multiple heat challenges, MEPP amplitude distributions were either uniform or were composed primarily of sub-MEPPs. MEPP time courses were slower after heat challenges, and in some preparations, inflections were observed on many MEPP rising phases. Amplitude histograms of these inflections yielded distributions similar to control distributions of skew-MEPPs.The presence of inflections on MEPPs following heat challenges supports the hypothesis that skew-MEPPs and bell-MEPPs are composed of subunits. These results suggest that skew- and bell-MEPPs are caused by the release of transmitter by different temperature-sensitive mechanisms.     

The effect of acetylcholine on the function and structure of the developing mammalian neuromuscular junction

Isolated soleus muscles from rats aged 9–12 days were exposed to acetylcholine for 2 h in normal Krebs solution. This treatment caused changes in the ultrastructural appearance of the neuro-muscular junction and a significant reduction of axon profiles per endplate. Nevertheless, most neuro-muscular junctions remained functional, since the ratio of the indirectly to directly elicited contraction was not reduced.If muscles were exposed to acetylcholine in Krebs solutions containing 12m M Ca²⁺ instead of the normal 1.9 m M, the ultrastructural changes produced by acetylcholine were more severe, and the number of axon terminals per endplate was further reduced so that many endplates became completely denervated. This was also reflected in the impaired function of the nerve-muscle preparation; the ratio of the indirectly to directly elicited contraction decreased and about 40% of the muscles fibres became functionally denervated. Addition of curare to the incubating medium prevented the functional deterioration of the preparation.Addition of the protease inhibitors leupeptin and pepstatin protected the nerve terminals from the damaging effects of acetylcholine in Krebs solution containing 12m M Ca²⁺ and the number of axon profiles per endplate remained normal. The functional deterioration was also much reduced when protease inhibitors were included in the incubation medium.These results suggest that acetylcholine causes the activation and release of proteolytic enzymes in developing muscles. The response is mediated by calcium and may have a role in the removal of superfluous nerve-muscle contacts during development.     

Spontaneous synchronization by 4-aminopyridine of acetylcholine release in the neuromuscular junction

The effect of 4-aminopyridine (4AP) on the character of acetylcholine release was investigated by intracellular recording of spontaneous synaptic activity in an isolated rate phrenic nervediaphragm preparation. No significant changes were found in the mean frequency and amplitude of miniature end-plate potentials (MEPP) in response to 4AP in concentrations of 1·10^–6 to 1·10^–3M. Meanwhile, 4AP caused the appearance of large spontaneous EPP capable of inducing spreading action potentials. 4AP changed the character of distribution of MEPP amplitudes, converting it to polymodal; in some cases the principal mode was shifted into the region of lower values. It is concluded that 4AP changes the character of acetylcholine release and potentiates spontaneous synchronization.Laboratory of General Pathology of the Nervous System, Institute of General Pathology and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Department of Pharmacology, Faculty of Internal Medicine and Hygiene, I. M. Sechenov First Moscow Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR A. M. Chernukh.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 88, No. 9, pp. 259–262, September, 1979.     

Noise analysis of acetylcholine induced current at neuromuscular junctions of the mouse diaphragm

Miniature end-plate currents (mepcs) and membrane noise elicited by acetylcholine (ACh) iontophoresis were investigated at neuromuscular junctions of the mouse diaphragm. All the experiments were performed at a holding potential of -70 mV at a temperature of 19 degrees C. The equilibrium potential of the ACh response was estimated to be near zero; the mepcs displayed a peak amplitude of 2.46 +/- 0.13 nA (mean +/- S.E.) and relaxed exponentially with a time constant to 1.63 +/- 0.11 msec. Single ACh-activated channels had a conductance of 26.5 +/- 1.5 pS and a mean life time of 1.69 +/0- 0.13 msec.     

Changes in spontaneous and evoked release of transmitter induced by the crotoxin complex and its component phospholipase A2 at the frog neuromuscular junction.

The time course and characteristics of the changes induced by the action of the crotoxin complex and of its component phospholipase A₂ on transmission at the frog neuromuscular junction was studiedin vitro at single endplates using intracellular recording techniques. Both the crotoxin complex and phospholipase A₂ induced variable changes in spontaneous transmitter release in which bursts of miniature endplate potentials alternated with periods when the frequency of miniature endplate potentials was stable but their amplitudes were markedly heterogeneous. The bursts of miniature endplate potentials were of sudden onset and of a high initial frequency, and their duration and incidence were highly variable both at one endplate and between endplates. These changes in the frequency and amplitude of miniature potentials occurred both before and after the abolition of neurally evoked endplate potentials and in the presence of tetrodotoxin. At a late stage in crotoxin intoxication, potassium depolarization of the motor nerve terminals failed to increase spontaneous transmitter release. Both the crotoxin complex and phospholipase A₂ reduced the amplitude of endplate potentials although phospholipase A₂ was less effective. The course of depression of the quantal content of evoked transmitter release induced by the crotoxin complex was occasionally interrupted by a brief facilitation of response; these irregularities in the rate of depression were more clearly seen when endplate potentials were recorded at partially curarized endplates exposed to either the crotoxin complex or to phospholipase A₂. At the stage of abolition of endplate potentials an increase in the external concentration of Ca^{2 +} enabled the evoked response to be restored temporarily. The crotoxin complex and phospholipase A₂ had no effect on the input resistance of the sarcolemmal membrane, but raised the threshold stimulus required to initiate an action potential at concentrations which affected transmitter release. Crotapotin did not affect any of the measured parameters even at high concentrations.The diversity of changes observed in the properties of spontaneous and evoked transmitter release, suggests that the crotoxin complex and phospholipase A₂ may induce two kinds of alterations in the structure of the presynaptic membrane as a result of the action of phospholipase A₂, viz (a) the formation of transient instabilities with an increased Ca^{2 +} inflow and (b) prolonged disturbance of the calcium channel and/or the synchronized release of subunits at the active zone.     

Changes in the distribution of the extrajunctional acetylcholine sensitivity along muscle fibers during development and following cordotomy in the rat

Acetylcholine sensitivity along the entire length of muscle fibers was studied during postnatal development and following transection of the spinal cord in the rat. During postnatal development, the acetylcholine sensitivity in the soleus and extensor digitorum longus muscles decreased faster at the juxtajunctional region than near the tendons. Thus, the adult pattern of low acetylcholine sensitivity at the extrajunctional membrane was achieved through the uneven change of acetylcholine sensitivity during normal development. This uneven pattern of the sensitivity was found to appear in both muscles in older rats after cordotomy, and is in striking contrast to the uniform pattern in denervated muscles. The uneven appearance of the sensitivity could not be explained by changes in input resistance or resting membrane potential. In the soleus muscle whose nerve was implanted at an ectopic site, the lowest sensitivity also appeared at the ectopic juxtajunctional region after cordotomy. These results indicate that the motor nerve exerts regionally different effects along a fiber with respect to the appearance of acetylcholine receptors.     

Effect of purines on calcium-independent acetylcholine release at the mouse neuromuscular junction

At the mouse neuromuscular junction, activation of adenosine A(1) and P2Y receptors inhibits acetylcholine release by an effect on voltage dependent calcium channels related to spontaneous and evoked secretion. However, an effect of purines upon the neurotransmitter-releasing machinery downstream of Ca(2+) influx cannot be ruled out. An excellent tool to study neurotransmitter exocytosis in a Ca(2+)-independent step is the hypertonic response. Intracellular recordings were performed on diaphragm fibers of CF1 mice to determine the action of the specific adenosine A(1) receptor agonist 2-chloro-N(6)-cyclopentyl-adenosine (CCPA) and the P2Y(12-13) agonist 2-methylthio-adenosine 5'-diphosphate (2-MeSADP) on the hypertonic response. Both purines significantly decreased such response (peak and area under the curve), and their effect was prevented by specific antagonists of A(1) and P2Y(12-13) receptors, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and N-[2-(methylthioethyl)]-2-[3,3,3-trifluoropropyl]thio-5'-adenylic acid, monoanhydride with dichloromethylenebiphosphonic acid, tetrasodium salt (AR-C69931MX), respectively. Moreover, incubation of preparations only with the antagonists induced a higher response compared with controls, suggesting that endogenous ATP/ADP and adenosine are able to modulate the hypertonic response by activating their specific receptors. To search for the intracellular pathways involved in this effect, we studied the action of CCPA and 2-MeSADP in hypertonicity in the presence of inhibitors of several pathways. We found that the effect of CPPA was prevented by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) while that of 2-MeSADP was occluded by the protein kinase C antagonist chelerythrine and W-7. On the other hand, the inhibitors of protein kinase A (N-(2[pbromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide, H-89) and phosphoinositide-3 kinase (PI3K) (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride, LY-294002) did not modify the modulatory action in hypertonicity of both purines. Our results provide evidence that activation of A(1) and P2Y(12-13) receptors by CCPA and 2-MeSADP inhibits ACh release from mammalian motor nerve terminals through an effect on a Ca(2+)-independent step in the cascade of the exocytotic process. Since presynaptic calcium channels are intimately associated with components of the synaptic vesicle docking and fusion processes, further experiments could clarify if the actions of purines on calcium channels and on secretory machinery are related.     

Presynaptic acetylcholine receptors at the excitatory amino acid synapse in locust muscle

Acetylcholine (greater than or equal to 10(-5) M) applied in the bathing medium to the excitatory nerve-muscle junction of the locust caused a dose-dependent increase in the frequency of spontaneous miniature potentials and in the mean quantal content of evoked potentials. The statistical characteristics of the spontaneous release process were also modified, high frequency bursts of spontaneous potentials and "giant' miniature potentials occurring in the presence of acetylcholine. The response, which was dependent on extracellular calcium concentration, consisted of two distinct phases; these could be induced or abolished selectively by nicotinic and muscarinic drugs, respectively. The results suggest the presence, in low density, of two types of cholinergic receptors on the excitatory motor nerve terminals of the locust. The acetylcholine-induced channels may admit calcium ions. The possible role of these presynaptic receptors is discussed.     

Stimulation of transmitter release by guanidine derivatives.

Guanidine and its alkylated derivatives stimulate transmitter release in the sciatic nerve-sartorius muscle preparation of the frog, the excitatory nerve-opener muscle preparation of the crayfish cheloped, and the phrenic nerve-diaphragm preparation of the rat. The mechanism underlying this action has been studied. The amplitude of the end-plate potential was increased by guanidine derivatives. Guanidine, methylguanidine, 1,1-dimethylguanidine, ethylguanidine and propylguanidine were almost equally potent with the threshold concentration of 0.1–0.2mM. Formamidine and aminoguanidine were 20–40 times less potent than guanidine. This effect was reversed slowly after washing with normal solution free of drugs. However, the frequency of miniature end-plate potentials was not affected by high concentrations (5–10mM) of guanidine, and no change was observed in membrane potential and input resistance following application of guanidine, methylguanidine and 1,1-dimethylguanidine. The iontophoretically induced acetylcholine potential was suppressed by methylguanidine, 1,1-dimethylguanidine, ethylguanidine and propylguanidine, and was restored quickly upon washing with normal solution. Based on the actions on the end-plate potential and on the iontophoretic acetylcholine potential, the order of the potencies of guanidine derivatives in stimulating transmitter release were estimated as: methylguanidine, 1,1-dimethylguanidine, ethylguanidine, propylguanidine > guanidine > aminoguanidine, formamidine. Amylguanidine and octylguanidine had no presynaptic effect.Increasing external calcium concentration from 1.8 mM to 6 or 12 mM did not prevent the stimulating action of guanidine and 1,1-dimethylguanidine on the end-plate potential. Methylguanidine and 1,1-dimethylguanidine did not seem to affect the time constant of decay of neuromuscular facilitation in the rat. The quantal content of the end-plate potential in the rat preparation was increased by methylguanidine and 1,1-dimethylguanidine, and this increase was due entirely to an increase in the immediately available store of acetylcholine in the nerve terminal. The probability of release remained constant. It is unlikely that this action is due to the inhibition of mitochondrial respiration.     

Distribution of spontaneous release along the frog neuromuscular junction

A new method, called the spatial decay method, is described. This method permits to localize the site of occurrence of the spontaneous release producing each miniature end-plate potential (MEPP) recorded at the frog neuromuscular junction (nmj). The method requires simultaneous intracellular recording at both distal ends of the nmj. The electrodes are positioned using Nomarksi optics. The assumptions that the MEPP amplitude is maximum in front of its release site and decays exponentially toward the recording electrodes placed distally, permit the calculation of the position of the release site producing each MEPP recorded intracellularly. The spatial decay method indicates that the occurrence of spontaneous release is not uniformly distributed along the frog nmj.     

Zinc competitively inhibits calcium-dependent release of transmitter at the mouse neuromuscular junction

The effect of zinc on the release of transmitter was investigated in preparations of mouse diaphragm by conventional microelectrode techniques. The frequency (FP of miniature end-plate potentials (MEPPs), elevated by Ca²⁺ in high K⁺ medium, was reduced by zinc in a concentration-dependent fashion. When the extracellular concentration of Ca²⁺ ([Ca²⁺]_o) was varied in the absence of zinc, a linear relationship between log(F) and log([Ca²⁺]_o) was obtained. When the effect of zinc was depicted graphically, it was found that zinc shifted the relationship between log(F) and log([Ca²⁺]_o) to the right, with respect to the control in the absence of zinc, without altering the slope. Zinc also reduced the quantal content (m) of end-plate potentials (EPPs). As [Ca²⁺]_o was varied in the absence of zinc, a linear relationship between ln(m) and ln([Ca²⁺]_o) was observed. Zinc shifted this linear relationship between ln(m) and ln([Ca²⁺]_o) to the right, with respect to the control, without altering the slope. Thus, zinc reduced both the asynchronous and the phasic release of transmitter. These results suggest that zinc competes with Ca²⁺, and this conclusion is confirmed by examination of a modified Lineweaver-Burk plot of the data. Zinc probably inhibits the entry of Ca²⁺ into the nerve terminals, thereby inhibiting transmitter release.     

Inhibition of non-quantal acetylcholine leakage by 2(4-phenylpiperidine)cyclohexanol in the mouse diaphragm

The drug 2(4-phenylpiperidine)cyclohexanol (AH 5183) caused hyperpolarization by 1.8 +/- 0.6 mV in an end-plate zone of mouse diaphragm fibers without any change in the amplitude of miniature end-plate potentials. This supports the idea that the drug inhibits the non-quantal leakage from motor nerve terminals, probably at those parts of the nerve terminals which were incorporated into the terminal membrane after vesicle exocytosis.