Ca2+ inhibits outward current through single K+ channels in canine atrial myocyte sarcolemma.
Single-channel currents in canine atrial cells were recorded by the patch-clamp technique in a bathing solution containing 150 mM [K+] and pipette solutions containing 5 mM [K+]. One kind of current was observed in 56% of 178 cell-free patches and in 3% of 60 patches in the cell-attached configuration. Single-channel amplitude varied in direct proportion to the bath [K+]. Openings of these single channels were prevented when bath [Ca2+] exceeded 1 microM. Below this concentration single-channel percent open time was inversely proportional to log [Ca2+]. Inward current was observed at hyperpolarized membrane potentials in some patches. There was no apparent steady-state voltage sensitivity. These properties suggest that the K+ channel described in this study (gK+LF), a low transition frequency K+ conductor, may be distinct from single K+ channels previously studied in cardiac myocyte sarcolemmae. The single-channel response to "intracellular" free [Ca2+] and the single-channel kinetic characteristics described in this study are similar to the macroscopic "long-lasting transient outward current" (IIO) described by Escande et al. [Am. J. Physiol. 252 (Heart Circ. Physiol. 21): H142-H148, 1987] in human atrial myocytes (tau open = 29.6 ms, tau inactivation = 35.7 ms, respectively). This suggests that gK+LF channels may carry IIO.
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004285:Dogs; D006325:Heart Atria; D007425:Intracellular Membranes / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects* / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism*; D012508:Sarcolemma / Q000378:metabolism*
D007473:Ion Channels; D011188:Potassium; D002118:Calcium