The Journal of Membrane Biology

, Volume 111, Issue 1, pp 57–67 | Cite as

Barium- and calcium-permeable channels open at negative membrane potentials in rat ventricular myocytes

  • Alain Coulombe
  • Isabel Ann Lefèvre
  • Isabelle Baro
  • Edouard Coraboeuf
Articles

Summary

Ca2+- and Ba2+-permeable channel activity from adult rat ventricular myocytes, spontaneously appeared in the three single-channel recording configurations: cell-attached, and excised inside-out or outside-out membrane patches. Single-channel activity was recorded at steady-state applied membrane potentials including the entire range of physiologic values, and displayed no “rundown” in excised patches. This activity occurred in irregular bursts separated by quiescent periods of 5 to 20 min in cell-attached membrane patches, whereas in excised patch experiments, this period was reduced to 2 to 10 min. During activity, a variety of kinetic behaviors could be observed with more or less complex gating patterns. Three conductance levels: 22, 45 and 78 pS were routinely observed in the same excised membrane patch, sometimes combining to give a larger level. These channels were significantly permeable to divalent cations and showed little or no permeability to potassium or sodium ions. The inorganic blockers of voltage-gated Ca channels, cobalt (2mm), cadmium (0.5mm) or nickel (3mm), had no apparent effect on these spontaneous unitary currents carried by barium ions. Under 10−5m bay K 8644 or nitrendipine, the activity was clearly increased in about half of the tested excised inside-out membrane patches. Both dihydropyridines enhanced openings of the larger conductance level, which was only very occasionally seen under control conditions. When the single-channel activity became sustained under 5×10−6m Bay K 8644, it was possible to calculate the mean unitary current at different membrane potentials and show that the mean current value increased with membrane potential.

Key Words

cardiac myocytes single-channel recordings calcium background channels dihydropyridines voltage dependence 

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Copyright information

© Springer-Verlag New York Inc 1989

Authors and Affiliations

  • Alain Coulombe
    • 1
  • Isabel Ann Lefèvre
    • 1
  • Isabelle Baro
    • 1
  • Edouard Coraboeuf
    • 1
  1. 1.Laboratoire de Physiologie Comparée et Laboratoire des Biomembranes et des Ensembles Neuronaux (CNRS URA 1121)Université Paris-XIOrsay Cedex

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