Pflügers Archiv

, Volume 361, Issue 2, pp 145–151 | Cite as

Voltage dependence of agonist responses at voltage-clamped frog endplates

  • P. R. Adams


The conductance increment produced at voltage clamped frog endplates by various agonists, applied either iontophoretically or in the bath, increases exponentially with membrane hyperpolarisation, an e-fold change being obtained with shifts of the order of 100 mV. The voltage dependency of this increase is the same for different, but low, agonist concentrations. However, conductance changes evoked by decamethonium increased less with hyperpolarisation than did conductance changes evoked by carbachol or tetramethylammonium. Hyperpolarisation slowed iontophoretic responses to carbachol or decamethonium, and enhanced and prolonged inhibition of carbachol by a brief pulse of decamethonium.

Key words

Frog endplate Agonist conductance Voltage dependence 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Adams, P. R.: A comparison of the rate of onset of excitation and inhibition by decamethonium acting at frog endplate receptors. Brit. J. Pharmacol.51, 132P (1974)Google Scholar
  2. Adams, P. R.: Kinetics of agonist conductance changes during hyperpolarization at frog endplates. Brit. J. Pharmacol.53, 308–310 (1975a)Google Scholar
  3. Adams, P. R.: A study of desensitization using voltage clamp. Pflügers Arch.360, 135–144 (1975b)Google Scholar
  4. Adams, P. R.: An analysis of the dose-response curve at voltage-clamped frog endplates. Pflügers. Arch.360, 145–153 (1975c)Google Scholar
  5. Anderson, C. R., Stevens, C. F.: Voltage clamp analysis of acetylcholine produced end-plate current fluctuations at frog neuromuscular junction. J. Physiol. (Lond.)235, 655–691 (1973)Google Scholar
  6. del Castillo, J., Katz, B.: Interaction at endplate receptors between different choline derivatives. Proc. roy. Soc. B146, 369–381 (1957)Google Scholar
  7. Dionne, V. E., Stevens, C. F.: Voltage dependence of agonist effectiveness at the frog neuromuscular junction: Resolution of a paradox. J. Physiol. (Lond.) (in press, 1975)Google Scholar
  8. Dreyer, F., Peper, K.: Acetylcholine receptors: density and doseresponse curve in frog neuromuscular junction. Nature (Lond.)253, 641–643 (1975)Google Scholar
  9. Feltz, A., Mallart, A.: An analysis of acetylcholine responses of junctional and extrajunctional receptors of frog muscle fibres. J. Physiol. (Lond.)218, 85–100 (1971)Google Scholar
  10. Gage, P. W., Eisenberg, R. S.: Capacitance of the surface membrane and transvers tubular membrane of frog sartorius muscle fibres. J. gen. Physiol.53, 265–278 (1969)Google Scholar
  11. Gage, P. W., McBurney, R. N.: Effects of membrane potential, temperature and neostigmine on the conductance change caused by a quantum of acetylcholine at the toad neuromuscular junction. J. Physiol. (Lond.)244, 385–407 (1975)Google Scholar
  12. Hodgkin, A. L., Horowicz, P.: The differential action of hypertonic solutions on the twitch and action potential of a muscle fibre. J. Physiol. (Lond.)136, 17P (1957)Google Scholar
  13. Katz, B., Miledi, R.: The statistical nature of the acetylcholine potential and its molecular components. J. Physiol. (Lond.)224, 665–699 (1972)Google Scholar
  14. Katz, B., Miledi, R.: The binding of acetylcholine to receptors and its removal from the synaptic cleft. J. Physiol. (Lond.)231, 549–574 (1973)Google Scholar
  15. Kordaš, M.: The effect of membrane hyperpolarisation on the time course of the end-plate current in frog sartorius muscle. J. Physiol. (Lond.)204, 493–502 (1969)Google Scholar
  16. Lester, H. A., Changeux, J.-P., Sheridan, R. E.: Conductance increases produced by bath application of cholinergic agonists to Electrophorus electroplaques. J. gen Physiol.65, 797–816 (1975)Google Scholar
  17. Magazanik, L. G., Vyskočil, F.: Dependence of acetylcholine desensitization on the membrane potential of frog muscle fibre and on the ionic changes in the medium. J. Physiol. (Lond.)210, 507–518 (1970)Google Scholar
  18. Magleby, K. L., Stevens, C. F.: The effect of voltage on the time course of end-plate currents. J. Physiol. (Lond.)223, 151–171 (1972a)Google Scholar
  19. Magleby, K. L., Stevens, C. F.: A quantitative description of endplate currents. J. Physiol. (Lond.)223, 173–197 (1972b)Google Scholar
  20. 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. (Lond.)244, 467–495 (1975)Google Scholar
  21. Narahashi, T.: Chemicals as tools in the study of excitable membranes. Physiol. Rev.54, 813–889 (1974)Google Scholar
  22. Neher, E., Sakmann, B.: Voltage dependence of drug-induced conductance in frog neuromuscular junction. Proc. nat. Acad. Sci. (Wash.)72, 2140–2144 (1975)Google Scholar
  23. Rang, H. P., Quoted in Hammes, G. G., Molinoff, P. B., Bloom, F. E.: Receptor biophysics and chemistry. Neurosciences Res. Progr. Bull.11, 220–224 (1971)Google Scholar

Copyright information

© Springer-Verlag 1976

Authors and Affiliations

  • P. R. Adams
    • 1
  1. 1.Department of PharmacologySt. Bartholomew's Hospital Medical CollegeLondonUK

Personalised recommendations