Pflügers Archiv

, Volume 430, Issue 5, pp 871–878

[Ca2+]i-dependent membrane currents in guinea-pig ventricular cells in the absence of Na/Ca exchange

  • Karin R. Sipido
  • Geert Callewaert
  • Francesco Porciatti
  • Johan Vereecke
  • Edward Carmeliet
Original Article Heart, Circulation, Respiration and Blood; Environmental and Exercise Physiology

DOI: 10.1007/BF00386189

Cite this article as:
Sipido, K.R., Callewaert, G., Porciatti, F. et al. Pflugers Arch. (1995) 430: 871. doi:10.1007/BF00386189

Abstract

Transient inward currents (Iti) during oscillations of intracellular [Ca2+] ([Ca2+]i) in ventricular myocytes have been ascribed to Na/Ca exchange. We have investigated whether other Ca2+-dependent membrane currents contribute to Iti in single guinea-pig ventricular myocytes, by examining membrane currents during [Ca2+]i oscillations and during caffeine-induced Ca2+ release from the sarcoplasmic reticulum in the absence of Na+. Membrane currents were recorded during whole-cell voltage clamp and [Ca2+]i measured simultaneously with fura-2. In the absence of Na/Ca exchange, i.e., with Li+, Cs+ or N-methyl-D-glucamine (NMDG+) substituted for Na+, the cell could be loaded with Ca2+ by repetitive depolarizations to +10 mV, resulting in spontaneous [Ca2+]i oscillations. During these oscillations, no inward currents were seen, but instead spontaneous Ca2+ release was accompanied by a shift of the membrane current in the outward direction at potentials between −40 mV and +60 mV. This [Ca2+]i-dependent outward current shift was not abolished when NMDG+ was substituted for internal monovalent cations, nor was it sensitive to substitution of external Cl. It was however, sensitive to the blockade of ICa by verapamil. These results suggest that the transient outward current shift observed during spontaneous Ca2+ release represents [Ca2+]idependent transient inhibition of ICa. Similarly, during the [Ca2+]i transients induced by brief caffeine (10 mM) applications, we could not detect membrane currents attributable to a Ca2+-activated nonselective cation channel, or to a Ca2+-activated Cl channel; however, transient Ca2+-dependent inhibition of ICa was again observed. We conclude that neither the Ca2+-activated nonselective cation channel nor the Ca2+-activated Cl channel contribute significantly to the membrane currents during spontaneous [Ca2+]i oscillations in guineapig ventricular myocytes. However, in the voltage range between −40 mV and +60 mV Ca2+-dependent transient inhibition of ICa will contribute to the oscillations of the membrane current.

Key words

Calcium oscillations Calcium current Nonspecific cation channel [Ca2+]i-dependent Cl current 

Copyright information

© Springer-Verlag 1995

Authors and Affiliations

  • Karin R. Sipido
    • 1
  • Geert Callewaert
    • 1
  • Francesco Porciatti
    • 2
  • Johan Vereecke
    • 1
  • Edward Carmeliet
    • 1
  1. 1.Laboratory of physiologyKatholieke Universiteit LeuvenLeuvenBelgium
  2. 2.Department of PharmacologyUniversity of FlorenceFlorenceItaly

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