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Pflügers Archiv

, Volume 377, Issue 3, pp 193–200 | Cite as

Relaxation of the ACh-induced potassium current in the rabbit sinoatrial node cell

  • A. Noma
  • W. Trautwein
Excitable Tissues and Central Nervous Physiology

Abstract

Voltage clamp experiments were carried out in order to study the mechanism of the ACh action in the rabbit S-A node cell. The following results were obtained:
  1. 1.

    The reversal potential of the ACh-induced current behaved like a potassium electrode, confirming that the ACh-operated channels pass potassium ions selectively.

     
  2. 2.

    On depolarizing voltage jumps the ACh-induced current showed an instantaneous peak from which the current decayed to a new steady level (relaxation). On hyperpolarizing voltage jumps the initial step change in current was followed by a gradual increase.

     
  3. 3.

    The time course of the current change on voltage jumps was well fitted by a single exponential and the time constant became longer as the membrane potential was increased.

     
  4. 4.

    The instantaneous I–V curve was linear while in the steady state the curve became flatter at low negative membrane potentials and steeper at high negative membrane potentials.

     

The results suggest that ACh opens a specific potassium channel when the drug is bound to the muscarinic receptor. The opening and closing rate constants for this potassium channel depend on the membrane potential in such a way that on depolarizing voltage jumps the fraction of open channels gradually decreases and on hyperpolarization the fraction increases.

Key words

S-A node Voltage clamp ACh-induced current Relaxation 

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References

  1. Adams, P. R.: Kinetics of agonist conductance changes during hyperpolarization at frog endplates. Br. J. Pharmacol.53, 308–310 (1974)Google Scholar
  2. Anderson, C. R., Stevens, C. F.: Voltage clamp analysis of acetylcholine produced current fluctuations at frog neuromuscular junction. J. Physiol. (Lond.)235, 655–691 (1973)Google Scholar
  3. Beeler, G. W., Reuter, H.: Reconstruction of the action potential of ventricular myocardial fibres. J. Physiol. (Lond.)268, 177–210 (1977)Google Scholar
  4. Dreyer, F., Peper, K.: Iontophoretic application of acetylcholine: Advantages of high resistance micropipettes in connection with an electronic current pump. Pflügers Arch.348, 263–272 (1974)Google Scholar
  5. Giles, W. R., Noble, S. J.: Changes in membrane currents in bullfrog atrium produced by acetylcholine. J. Physiol. (Lond.)261, 103–123 (1976)Google Scholar
  6. Glitsch, H. G., Pott, L.: Effects of acetylcholine and parasympathetic nerve stimulation on membrane potential in quiescent guinea pig atria. J. Physiol. (Lond.)279, 655–668 (1978)Google Scholar
  7. Harris, E. J., Hutter, O. F.: The action of acetylcholine on the movements of potassium ions in the sinus venosus of the heart. J. Physiol. (Lond.)133, 58P (1956)Google Scholar
  8. Hutter, O. F.: Ion movement during vagus inhibition of the heart. In: Nervous inhibition (E. Florey, ed.), pp. 114–123. Oxford: Pergamon Press 1961Google Scholar
  9. Ikemoto, Y., Goto, M.: Nature of the negative inotropic effect of acetylcholine on the myocardium. An elucidation of the bullfrog atrium. Proc. Jap. Acad.51, 501–505 (1975)Google Scholar
  10. Katz, B., Miledi, R.: The statistical nature of the acetylcholine potential and its molecular components. J. Physiol. (Lond.)224, 665–699 (1972)Google Scholar
  11. McAllister, R. E., Noble, D., Tsien, R. W.: Reconstruction of the electrical activity of cardiac Purkinje fibers. J. Physiol. (Lond.)251, 1–59 (1975)Google Scholar
  12. McDonald, T. F., Trautwein, W.: The potassium current underlying delayed rectification in cat ventricular muscle. J. Physiol. (Lond.)274, 217–246 (1978)Google Scholar
  13. Neher, E., Sakmann, B.: Noise analysis of drug-induced voltage clamp currents in denervated frog muscle fibers. J. Physiol. (Lond.)258, 705–729 (1976)Google Scholar
  14. Noble, D., Tsien, R. W.: The kinetic and rectifier properties of the slow potassium current in cardiac Purkinje fibers. J. Physiol. (Lond.)195, 185–214 (1968)Google Scholar
  15. Noble, D., Tsien, R. W.: Outward membrane currents activated in the plateau range of potentials in cardiac Purkinje fibers. J. Physiol. (Lond.)200, 205–231 (1969)Google Scholar
  16. Noma, A., Irisawa, H.: Membrane currents in the rabbit sinoatrial node cell as studied by the double microelectrode method. Pflügers Arch.364, 45–52 (1976a)Google Scholar
  17. Noma, A., Irisawa, H.: A time- and voltage-dependent potassium current in the rabbit sinoatrial node cell. Pflügers Arch.366, 251–258 (1976b)Google Scholar
  18. Noma, A., Trautwein, W.: Fluctuations in ACh-induced potassium current in the rabbit S-A node cell. in preparation (1979)Google Scholar
  19. Noma, A., DiFrancesco, D., Trautwein, W.: Dose-response curve for acetylcholine (ACh) and carbamylcholine (CCh) in the rabbit SA-node. Pflügers Arch.377, R4 (1978)Google Scholar
  20. Rayner, B., Weatherall, N.: Acetylcholine and potassium movements in rabbit auricles. J. Physiol. (Lond.)146, 392–409 (1959)Google Scholar
  21. Reuter, H.: Localization of beta adrenergic receptors and effects of noradrenaline and cyclic nucleotides on action potentials, ionic currents and tension in mammalian cardiac muscle. J. Physiol. (Lond.)242, 429–451 (1974)Google Scholar
  22. Ten Eick, R., Nawrath, H., McDonald, T. F., Trautwein, W.: On the mechanism of the negative inotropic effect of acetylcholine. Pflügers Arch.361, 207–213 (1976)Google Scholar
  23. Trautwein, W., Dudel, J.: Zum Mechanismus der Membranwirkung des Acetylcholin an der Herzmuskelfaser. Pflügers Arch. ges. Physiol.266, 324–334 (1958)Google Scholar
  24. Tsien, R. W.: Effects of epinephrine on the pacemaker potassium current of cardiac Purkinje fibers. J. Gen. Physiol.64, 293–319 (1974)Google Scholar

Copyright information

© Springer-Verlag 1978

Authors and Affiliations

  • A. Noma
    • 1
  • W. Trautwein
    • 1
  1. 1.II. Physiologisches Institut der Universität des SaarlandesHomburg/SaarGermany

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