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Pflügers Archiv

, Volume 338, Issue 2, pp 115–123 | Cite as

Selective inhibition of the transmembrane Ca conductivity of mammalian myocardial fibres by Ni, Co and Mn ions

  • M. Kohlhardt
  • B. Bauer
  • H. Krause
  • A. Fleckenstein
Article

Summary

According to earlier studies on mammalian papillary muscles, Ni and Co ions reduce the Ca dependent mechanical response whilst the action potential persists. In order to clarify the mode of action of these cations together with those of Mn their effects on the transmembrane fast Na and of the slow Ca currents were studied in voltage clamp experiments using the double sucrose gap technique. By a conditioning clamping procedure the Ca current was separated from the Na current. The following results were obtained:
  1. 1.

    Ni ions (2 mM) and Co ions (2 mM) strongly depress the Ca conductivity of the membrane. The same blockade was observed under the influence of Mn ions (2 mM). Even in the continued presence of Ni, Co or Mn the transmembrane Ca conductivity can be restored to a varying degree by increasing the extracellular Ca concentration.

     
  2. 2.

    In contrast to this strong inhibitory effect on the transmembrane Ca inward movements the fast transient Na current is only slightly affected if at all.

     
  3. 3.

    Apart from their selective inhibitory action on the transmembrane Ca current, Co ions show some additional features a) enhancement of its inhibitory action by repeated membrane depolarizations. b) Co-induced replacement of the slow Ca inward current by a transitory fast inward current component, c) synergetic effects of Co with Ca in restricting the fast Na current.

     
  4. 4.

    The selective inhibition of the transmembrane Ca conductivity clearly demonstrates the existence of a separate channel for Ca which is independent from the fast Na channel of the membrane.

     

This dual membrane transport system allows the regulation of the Ca dependent process of excitation-contraction coupling independently of a simultaneous influence on excitation.

Key words

Transmembrane Ca Currents Transmembrane Na Currents Ni, Co, Mn Excitation-Contraction Coupling Separate Ca Channel 

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References

  1. Baker, P. F., Meves, H., Ridgway, E. B.: Phasic entry of calcium in response to depolarization of giant axons of Loligo forbesi. J. Physiol. (Lond.)215, 22 P (1971).Google Scholar
  2. Carmeliet, E., Vereecke, J.: Adrenaline and the plateau phase of the cardiac action potential. Pflügers Arch.313, 300 (1969).Google Scholar
  3. Fleckenstein, A., Tritthart, H., Fleckenstein, B., Herbst, A., Grün, G.: deEine neue Gruppe kompetitiver Ca++-Antagonisten (Iproveratril, D 600, Prenylamin) mit starken Hemmeffekten auf die elektro-mechanische Koppelung im Warmblütermyokard. Pflügers Arch.307, 25 (1969).Google Scholar
  4. Haas, H. G., Kern, R., Einwächter, H. M.: Electrical activity and metabolism in cardiac tissue. An experimental and theoretcial study. J. Membrane Biol.3, 180 (1970).Google Scholar
  5. Kaufmann, R., Fleckenstein, A.: Ca++-kompetitive elektro-mechanische Entkoppelung durch Ni++- und Co++-Ionen am Warmblüter-Myokard. Pflügers Arch. ges. Physiol.282, 290 (1965).Google Scholar
  6. Kohlhardt, M., Bauer, B., Krause, H., Fleckenstein, A.: Differentiation of the transmembrane Na and Ca channels in mammalian cardiac fibres by the use of specific inhibitors. Pflügers Arch.335, 309 (1972).Google Scholar
  7. Ochi, R.: The slow inward current and the action of manganese ions in guinea-pigs myocardium. Pflügers Arch.316, 81 (1970).Google Scholar
  8. Reuter, H., Beeler, G. W.: Calcium current and activation of contraction in ventricular myocardial fibres. Science163, 399 (1969).Google Scholar
  9. Rougier, O., Vassort, G., Garnier, D., Gargouil, Y. M., Coraboeuf, E.: Existence and role of a slow inward current during the frog atrial action potential. Pflügers Arch.308, 91 (1969).Google Scholar
  10. Rougier, O., Vassort, G., Stämpfli, R.: Voltage clamp experiments on frog atrial heart muscle fibres with the sucrose gap technique. Pflügers Arch. ges. Physiol.301, 91 (1968).Google Scholar
  11. Stämpfli, R.: A new method for measuring membrane potential with external electrodes. Experientia (Basel)10, 508 (1954).Google Scholar
  12. Vassort, G., Rougier, O., Garnier, D., Sauviat, M. P., Coraboeuf, E., Gargouil, Y. M.: Effects of adrenaline on membrane inward currents during the cardiac action potential. Pflügers Arch.309, 70 (1969).Google Scholar
  13. Vitek, M., Trautwein, W.: Die Wirkung von Mangan-Ionen auf Aktionpotential und Ionenströme der Purkinje-Faser. Pflügers Arch.319, 113 (1970).Google Scholar
  14. Weidmann, S.: Elektrophysiologie der Herzmuskelfaser. Bern-Stuttgart: Huber 1956.Google Scholar

Copyright information

© Springer-Verlag 1973

Authors and Affiliations

  • M. Kohlhardt
    • 1
  • B. Bauer
    • 1
  • H. Krause
    • 1
  • A. Fleckenstein
    • 1
  1. 1.Physiologisches InstitutUniversität FreiburgFreiburg i. Br.Germany

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