Skip to main content
NCBI home page
The Journal of General Physiology logoLink to The Journal of General Physiology
. 1984 Mar 1;83(3):435–468. doi: 10.1085/jgp.83.3.435

The time course of miniature endplate currents and its modification by receptor blockade and ethanol

PMCID: PMC2215641  PMID: 6325590

Abstract

Miniature endplate currents (MEPCs) recorded from mouse diaphragms with a point voltage clamp, without inhibition of acetylcholinesterase (AChE) and in the absence of any drug, showed in their decay phase consistent deviations from an exponential time course, consisting of (a) "curvature," a progressive increase of decay rate during most of the decay phase, followed by (b) "late" tails. Both phenomena persisted when MEPCs (and channel lifetime) were prolonged by ethanol. Curvature was increased by muscle fiber depolarization and decreased by hyperpolarization. Receptor blockade by (+)-tubocurarine, alpha- bungarotoxin, hexamethonium, or myasthenic IgG accelerated the decay of the main part of MEPCs and eliminated curvature; the time constant of MEPCs became close to the channel time constant. We conclude that curvature arises from repeated action of ACh with cooperativity in ACh- receptor interaction; the voltage sensitivity of curvature follows from the voltage sensitivity of channel closing. Ethanol, in addition to its effect to prolong channel lifetime, enhances the tendency of ACh to act more than once to open channels before being lost to the system. Analysis of the rising phase of the MEPC, in terms of driving functions, also indicated that ethanol promotes channel opening by ACh; this action can account for a substantial increase of MEPC height by ethanol when MEPCs are made small by receptor blockade. Driving functions were also voltage sensitive, in a manner indicating acceleration of channel opening, but reduction of channel conductance, with hyperpolarization. Poisoning or inhibition of AChE prolonged MEPCs without altering the duration of ionic channels. Since ethanol caused further prolongation of MEPCs after poisoning of AChE, with little change in MEPC height, we conclude that the extension of mean channel lifetime by ethanol is accompanied by a similar extension of ACh binding to receptors. After poisoning of AChE, MEPCs became very variable in time course and the decay rate (tau-1) was correlated with MEPC height with a slope of log tau vs. log height of 0.77 for MEPCs of greater than 60% mean size. This slope is larger than expected from cooperativity in ACh-receptor interaction. Correlation of tau and height of MEPCs also exists when AChE is intact; the slope of log tau vs. log height was 0.12 with or without prolongation of MEPCs by ethanol.

Full Text

The Full Text of this article is available as a PDF (2.0 MB).

Selected References

These references are in PubMed. This may not be the complete list of references from this article.

  1. Adams D. J., Gage P. W. Ionic currents in response to membrane depolarization in an Aplysia neurone. J Physiol. 1979 Apr;289:115–141. doi: 10.1113/jphysiol.1979.sp012728. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Adams P. R. Acetylcholine receptor kinetics. J Membr Biol. 1981 Feb 28;58(3):161–174. doi: 10.1007/BF01870902. [DOI] [PubMed] [Google Scholar]
  3. Anderson C. R., Stevens C. F. Voltage clamp analysis of acetylcholine produced end-plate current fluctuations at frog neuromuscular junction. J Physiol. 1973 Dec;235(3):655–691. doi: 10.1113/jphysiol.1973.sp010410. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Attwell D., Iles J. F. Synaptic transmission: ion concentration changes in the synaptic cleft. Proc R Soc Lond B Biol Sci. 1979 Nov 30;206(1162):115–131. doi: 10.1098/rspb.1979.0095. [DOI] [PubMed] [Google Scholar]
  5. Boyd N. D., Cohen J. B. Kinetics of binding of [3H]acetylcholine and [3H]carbamoylcholine to Torpedo postsynaptic membranes: slow conformational transitions of the cholinergic receptor. Biochemistry. 1980 Nov 11;19(23):5344–5353. doi: 10.1021/bi00564a031. [DOI] [PubMed] [Google Scholar]
  6. Bradley R. J., Peper K., Sterz R. Postsynaptic effects of ethanol at the frog neuromuscular junction. Nature. 1980 Mar 6;284(5751):60–62. doi: 10.1038/284060a0. [DOI] [PubMed] [Google Scholar]
  7. Cohen I., van der Kloot W., Attwell D. The timing of channel opening during miniature end-plate currents. Brain Res. 1981 Oct 26;223(1):185–189. doi: 10.1016/0006-8993(81)90821-0. [DOI] [PubMed] [Google Scholar]
  8. Colquhoun D., Large W. A., Rang H. P. An analysis of the action of a false transmitter at the neuromuscular junction. J Physiol. 1977 Apr;266(2):361–395. doi: 10.1113/jphysiol.1977.sp011772. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. Cooke J. D., Quastel D. M. Transmitter release by mammalian motor nerve terminals in response to focal polarization. J Physiol. 1973 Jan;228(2):377–405. doi: 10.1113/jphysiol.1973.sp010092. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. DEL CASTILLO J., KATZ B. Biophysical aspects of neuro-muscular transmission. Prog Biophys Biophys Chem. 1956;6:121–170. [PubMed] [Google Scholar]
  11. DEL CASTILLO J., KATZ B. Localization of active spots within the neuromuscular junction of the frog. J Physiol. 1956 Jun 28;132(3):630–649. doi: 10.1113/jphysiol.1956.sp005554. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Dreyer F., Müller K. D., Peper K., Sterz R. The M. omohyoideus of the mouse as a convenient mammalian muscle preparation. A study of junctional and extrajunctional acetylcholine receptors by noise analysis and cooperativity. Pflugers Arch. 1976 Dec 28;367(2):115–122. doi: 10.1007/BF00585146. [DOI] [PubMed] [Google Scholar]
  13. Dreyer F., Peper K., Sterz R. Determination of dose-response curves by quantitative ionophoresis at the frog neuromuscular junction. J Physiol. 1978 Aug;281:395–419. doi: 10.1113/jphysiol.1978.sp012430. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Dunn S. M., Raftery M. A. Multiple binding sites for agonists on Torpedo californica acetylcholine receptor. Biochemistry. 1982 Nov 23;21(24):6264–6272. doi: 10.1021/bi00267a035. [DOI] [PubMed] [Google Scholar]
  15. Dwyer T. M. The rising phase of the miniature endplate current at the frog neuromuscular junction. Biochim Biophys Acta. 1981 Aug 6;646(1):51–60. doi: 10.1016/0005-2736(81)90271-6. [DOI] [PubMed] [Google Scholar]
  16. FATT P., KATZ B. Spontaneous subthreshold activity at motor nerve endings. J Physiol. 1952 May;117(1):109–128. [PMC free article] [PubMed] [Google Scholar]
  17. Feltz A., Large W. A., Trautmann A. Analysis of atropine action at the frog neutromuscular junction. J Physiol. 1977 Jul;269(1):109–130. doi: 10.1113/jphysiol.1977.sp011895. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Feltz A., Trautmann A. Interaction between nerve-related acetylcholine and bath applied agonists at the frog end-plate. J Physiol. 1980 Feb;299:533–552. doi: 10.1113/jphysiol.1980.sp013141. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Gage P. W., McBurney R. N., Schneider G. T. Effects of some aliphatic alcohols on the conductance change caused by a quantum of acetylcholine at the toad end-plate. J Physiol. 1975 Jan;244(2):409–429. doi: 10.1113/jphysiol.1975.sp010806. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Gage P. W. The effect of methyl, ethyl and n-propyl alcohol on neuromuscular transmission in the rat. J Pharmacol Exp Ther. 1965 Nov;150(2):236–243. [PubMed] [Google Scholar]
  21. Hartzell H. C., Kuffler S. W., Yoshikami D. Post-synaptic potentiation: interaction between quanta of acetylcholine at the skeletal neuromuscular synapse. J Physiol. 1975 Oct;251(2):427–463. doi: 10.1113/jphysiol.1975.sp011102. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Horn R., Brodwick M. S. Acetylcholine-induced current in perfused rat myoballs. J Gen Physiol. 1980 Mar;75(3):297–321. doi: 10.1085/jgp.75.3.297. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. KATZ B., THESLEFF S. A study of the desensitization produced by acetylcholine at the motor end-plate. J Physiol. 1957 Aug 29;138(1):63–80. doi: 10.1113/jphysiol.1957.sp005838. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Katz B., Miledi R. A re-examination of curare action at the motor endplate. Proc R Soc Lond B Biol Sci. 1978 Dec 4;203(1151):119–133. doi: 10.1098/rspb.1978.0096. [DOI] [PubMed] [Google Scholar]
  25. Katz B., Miledi R. The binding of acetylcholine to receptors and its removal from the synaptic cleft. J Physiol. 1973 Jun;231(3):549–574. doi: 10.1113/jphysiol.1973.sp010248. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Katz B., Miledi R. The nature of the prolonged endplate depolarization in anti-esterase treated muscle. Proc R Soc Lond B Biol Sci. 1975 Dec 31;192(1106):27–38. doi: 10.1098/rspb.1975.0149. [DOI] [PubMed] [Google Scholar]
  27. Kordás M., Brzin M., Majcen Z. A comparison of the effect of cholinesterase inhibitors on end-plate current and on cholinesterase activity in frog muscle. Neuropharmacology. 1975 Nov;14(11):791–800. doi: 10.1016/0028-3908(75)90106-9. [DOI] [PubMed] [Google Scholar]
  28. Kriebel M. E., Gross C. E. Multimodal distribution of frog miniature endplate potentials in adult denervated and tadpole leg muscle. J Gen Physiol. 1974 Jul;64(1):85–103. doi: 10.1085/jgp.64.1.85. [DOI] [PMC free article] [PubMed] [Google Scholar]
  29. Land B. R., Salpeter E. E., Salpeter M. M. Acetylcholine receptor site density affects the rising phase of miniature endplate currents. Proc Natl Acad Sci U S A. 1980 Jun;77(6):3736–3740. doi: 10.1073/pnas.77.6.3736. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Land B. R., Salpeter E. E., Salpeter M. M. Kinetic parameters for acetylcholine interaction in intact neuromuscular junction. Proc Natl Acad Sci U S A. 1981 Nov;78(11):7200–7204. doi: 10.1073/pnas.78.11.7200. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Landau E. M. Function and structure of the ACh receptor at the muscle end-plate. Prog Neurobiol. 1978;10(4):253–288. doi: 10.1016/0301-0082(78)90005-9. [DOI] [PubMed] [Google Scholar]
  32. Linder T. M., Quastel D. M. A voltage-clamp study of the permeability change induced by quanta of transmitter at the mouse end-plate. J Physiol. 1978 Aug;281:535–558. doi: 10.1113/jphysiol.1978.sp012438. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Magleby K. L., Stevens C. F. A quantitative description of end-plate currents. J Physiol. 1972 May;223(1):173–197. doi: 10.1113/jphysiol.1972.sp009840. [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Magleby K. L., Stevens C. F. The effect of voltage on the time course of end-plate currents. J Physiol. 1972 May;223(1):151–171. doi: 10.1113/jphysiol.1972.sp009839. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Magleby K. L., Terrar D. A. Factors affecting the time course of decay of end-plate currents: a possible cooperative action of acetylcholine on receptors at the frog neuromuscular junction. J Physiol. 1975 Jan;244(2):467–495. doi: 10.1113/jphysiol.1975.sp010808. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Mallart A., Molgó J. The effects of pH and curare on the time course of end-plate currents at the neuromuscular junction of the frog. J Physiol. 1978 Mar;276:343–352. doi: 10.1113/jphysiol.1978.sp012238. [DOI] [PMC free article] [PubMed] [Google Scholar]
  37. Manalis R. S. Voltage-dependent effect of curare at the frog neuromuscular junction. Nature. 1977 May 26;267(5609):366–368. doi: 10.1038/267366a0. [DOI] [PubMed] [Google Scholar]
  38. Milne R. J., Byrne J. H. Effects of hexamethonium and decamethonium on end-plate current parameters. Mol Pharmacol. 1981 Mar;19(2):276–281. [PubMed] [Google Scholar]
  39. Pennefather P., Quastel D. M. Relation between subsynaptic receptor blockade and response to quantal transmitter at the mouse neuromuscular junction. J Gen Physiol. 1981 Sep;78(3):313–344. doi: 10.1085/jgp.78.3.313. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Pennefather P., Quastel D. M. The effects of myasthenic IgG on miniature end-plate currents in mouse diaphragm. Life Sci. 1980 Dec 1;27(22):2047–2054. doi: 10.1016/0024-3205(80)90483-x. [DOI] [PubMed] [Google Scholar]
  41. Pressman B. C. Properties of ionophores with broad range cation selectivity. Fed Proc. 1973 Jun;32(6):1698–1703. [PubMed] [Google Scholar]
  42. Quastel D. M., Hackett J. T., Cooke J. D. Calcium: is it required for transmitter secretion? Science. 1971 Jun 4;172(3987):1034–1036. doi: 10.1126/science.172.3987.1034. [DOI] [PubMed] [Google Scholar]
  43. TAKEUCHI A., TAKEUCHI N. Active phase of frog's end-plate potential. J Neurophysiol. 1959 Jul;22(4):395–411. doi: 10.1152/jn.1959.22.4.395. [DOI] [PubMed] [Google Scholar]
  44. TAKEUCHI A., TAKEUCHI N. On the permeability of end-plate membrane during the action of transmitter. J Physiol. 1960 Nov;154:52–67. doi: 10.1113/jphysiol.1960.sp006564. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Takeda K., Barry P. H., Gage P. W. Effects of ammonium ions on endplate channels. J Gen Physiol. 1980 May;75(5):589–613. doi: 10.1085/jgp.75.5.589. [DOI] [PMC free article] [PubMed] [Google Scholar]
  46. Wathey J. C., Nass M. M., Lester H. A. Numerical reconstruction of the quantal event at nicotinic synapses. Biophys J. 1979 Jul;27(1):145–164. doi: 10.1016/S0006-3495(79)85208-X. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. van Helden D. F., Gage P. W., Hamill O. P. Conductance of end-plate channels is voltage dependent. Neurosci Lett. 1979 Feb;11(2):227–232. doi: 10.1016/0304-3940(79)90133-2. [DOI] [PubMed] [Google Scholar]

Articles from The Journal of General Physiology are provided here courtesy of The Rockefeller University Press

RESOURCES