AJP - Cell Physiology, Vol 254, Issue 3 C397-C403, Copyright © 1988 by American Physiological Society
Ca2+ inhibits outward current through single K+ channels in canine atrial myocyte sarcolemma
J. K. Bubien, H. Van Der Heyde and W. T. Woods Jr
Department of Physiology and Biophysics, University of Alabama, Birmingham 35294.
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.
