Advertisement

Pflügers Archiv

, Volume 334, Issue 1, pp 1–23 | Cite as

Inward membrane currents in mammalian myocardium

  • W. New
  • W. Trautwein
Article

Summary

  1. 1.

    Voltage clamp experiments (intracellular electrode for voltage control, current applied through a sucrose gap) were carried out in cat myocardium with an improved clamp circuit. The improvements were: a) reduction of series resistance by clamping the extracellular bath to earth potential and b) monitoring the longitudinal core resistancer ig of the fibres and the shunt resistancer eg in the gap.

     
  2. 2.

    Ratios ofr ig /r eg <1 (usually due to increase ofr ig because of decoupling of the cells in the gap) cause artifactual current wave forms of the configuration of a more or less suppressed “action potential”. The artifactual component of the recorded current flows through the shunt resistance.

     
  3. 3.

    In most preparations, shorter than 1 mm, cable properties do not permit space clamp (tested with a second intracellular electrode). Both the rapid sodium current and a slow inward current differing in threshold, amplitude and time course “escape” and produce voltage gradients making measurement of membrane current incorrect. In these preparations the configuration of the current trace depends on the position of the intracellular electrode in the voltage control circuit.

     
  4. 4.

    In preparations of suitable geometry, smallr ig /r eg ratio and small series resistance space clamp is achieved. Under this condition the two inward currents are clearly separated from each other.

     
  5. 5.

    The threshold of the slow inward current is at −35 mV. The maximum amplitude of the slow inward current amounts to 1–5 μA (preparation length and diameter about 0.5 mm). A plot of h vs. membrane potential shows inactivation of the slow inward current between −50 mV and −20 mV.

     
  6. 6.

    Following a depolarization step the slow inward current is turned on with a delay of a few milliseconds. Its activation time amounts to about 20 ms at threshold and 6–8 ms at zero potential. Its inactivation time constant amounts to 60–70 ms between −25 mV and +10 mV, being much longer outside this range.

     

Key words

Voltage Clamp Rapid and Slow Inward Current Mammalian Myocardium 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Adrian, R. H., Chandler, W. K., Hodgkin, A. L.: Voltage clamp experiments in striated muscle fibres. J. Physiol. (Lond.)208, 607–644 (1970).Google Scholar
  2. Beeler, G. W., Jr., Reuter, H.: Membrane calcium current in ventricular myocardial fibres. J. Physiol. (Lond.)207, 191–209 (1970b).Google Scholar
  3. ——: Voltage clamp experiments on ventricular myocardial fibres. J. Physiol. (Lond.)207, 165–190 (1970a).Google Scholar
  4. Bezanilla, F., Rojas, E., Taylor, R. E.: Sodium and potassium conductance changes during a membrane action potential. J. Physiol. (Lond.)211, 729–751 (1970).Google Scholar
  5. Cole, K. S.: An analysis of the membrane potential along a clamped squid axon. Biophys. J.1, 401–418 (1961).Google Scholar
  6. —: Membranes, Ions and Impulses. Berkeley, California: University of California Press 1968.Google Scholar
  7. Giebisch, G., Weidmann, S.: Membrane currents in mammalian ventricular heart muscle fibres using a voltage clamp technique. J. gen. Physiol.57, 290–296 (1971).Google Scholar
  8. Hodgkin, A. L., Huxley, A. F., Katz, B.: Measurement of current-voltage relations in the membrane of the giant axon of Loligo. J. Physiol. (Lond.)116, 424–448 (1952).Google Scholar
  9. Johnson, E. A., Lieberman, M.: Heart: excitation and contraction. Ann. Rev. Physiol.33, 479–532 (1971).Google Scholar
  10. Mascher, D., Peper, K.: Two components of inward current in myocardial muscle fibers. Pflügers Arch.307, 190–203 (1969).Google Scholar
  11. Moore, J. W., Cole, K. S.: Voltage clamp techniques. In: Physical Techniques in Biological Research, G. Oster, ed., vol. 6, pp. 263–321. New York: Academic Press 1963.Google Scholar
  12. Ochi, R.: The slow inward current and the action of manganese ions on guinea pig's myocardium. Pflügers Arch.316, 81–94 (1970).Google Scholar
  13. Rougier, O., Vassort, G., Garnier, G., Gargouil, Y. M., Coraboeuf, E.: Existence and role of a slow inward current during the frog atrial action potential. Pflügers Arch.308, 91–110 (1969).Google Scholar
  14. ——, Stämpfli, R.: Voltage clamp experiments on frog atrial heart muscle fibres with the sucrose gap technique. Pflügers Arch. ges. physiol.301, 91–108 (1968).Google Scholar
  15. Schilling, M. O.: Capacitance transducers for muscle research. Rev. Sci. Inst.31, 1215–1217 (1960).Google Scholar
  16. Taylor, R. E., Moore, J. W., Cole, K. S.: Analysis of certain errors in squid axon voltage clamp measurements. Biophys. J.1, 161–202 (1960).Google Scholar

Copyright information

© Springer-Verlag 1972

Authors and Affiliations

  • W. New
    • 1
    • 2
  • W. Trautwein
    • 1
    • 2
  1. 1.Department of PhysiologyUniversity of California at Los Angeles, Center for Health SciencesLos Angeles
  2. 2.Los Angeles Country Cardiovascular Research LaboratoryUniversity of California at Los Angeles, Center for Health SciencesLos Angeles

Personalised recommendations