Barium- and calcium-permeable channels open at negative membrane potentials in rat ventricular myocytes.
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 (2 mM), cadmium (0.5 mM) or nickel (3 mM), had no apparent effect on these spontaneous unitary currents carried by barium ions. Under 10(5) M 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 x 10(-6) M 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.
Coulombe
A
A
Laboratoire de Physiologie Comparée, Laboratoire des Biomembranes, des Ensembles Neuronaux (CNRS URA 1121), Université Paris-XI, Orsay.
Lefèvre
I A
IA
Baro
I
I
Coraboeuf
E
E
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009206:Myocardium / Q000378:metabolism*; D009568:Nitrendipine / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism
D015220:Calcium Channels; D001464:Barium; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009568:Nitrendipine; D012964:Sodium; D011188:Potassium