Ca2+-activated nonselective cation channels in rat neonatal atrial myocytes

A nonselective cation channel activated by intracellular Ca2+ was identified in inside-out membrane patches taken from cultured rat atrial myocytes. Ca2+ (0.01-1.00 mm) reversibly activated the channel in a concentration-dependent manner. The channel often showed a quick and irreversible rundown within a few minutes after patch excision. The I-V relationship of the channel was linear between -100 and +100 mV. The single channel conductance was 26.0 +/- 0.5 pS and its open probability was weakly voltage-dependent. Ion-substitution experiments showed that the channel was permeable to monovalent cations (P-x/P-Cs: Li+ (1.5) = K+ (1.5) > Na+ (1.2) > Rb+ (1.1) > Cs+ (1.0)) but not to Cl-(P-Cl/P-Cs < 0.01) and Ca2+ (P-Ca/P-Cs = 0.02 +/- 0.01).