AJP - Cell Physiology, Vol 262, Issue 1 C84-C90, Copyright © 1992 by American Physiological Society
Calcium-dependent inactivation of inwardly rectifying K+ channel in a tumor mast cell line
M. Mukai, I. Kyogoku and M. Kuno
Department of Physiology, Osaka City University Medical School, Japan.
Antigenic stimulation of rat basophilic leukemia (RBL-2H3) cells, a tumor
mast cell line, is associated with an increase in intracellular free Ca2+
concentrations ([Ca2+]i) and membrane polarization. We recorded whole cell
and single-channel currents through the inwardly rectifying K+ channel, a
major resting conductance of cells, using the patch-clamp technique, and we
examined interactions between channel activity and [Ca2+]i. With 10 microM
Ca2+ in the pipette, the amplitude of whole cell currents gradually
declined within 5 min to 48 +/- 13% of that immediately after rupture of
the patch membrane, in the presence of 1 mM ATP which minimized intrinsic
rundown. In inside-out patches, activity of the channel was reduced by
increasing the concentration of Ca2+ in the internal medium, both in the
presence and absence of 1 mM ATP, with no apparent change in single-channel
conductance. Time-averaged mean current activity in inside-out patches in
the presence of 5 microM Ca2+ was less than 50% of that with Ca2+ of 100 nM
or less. These results suggest that a rise in [Ca2+]i leads to a closure of
the inwardly rectifying K+ channel. In some inside-out patches, inward
currents characterized by burst composed of rapid transitions between open
and closed states were observed (flickering currents). Single-channel
properties of the flickering currents are similar to the inwardly
rectifying K+ channel except for kinetics (single-channel conductance of
24.5 +/- 7.9 pS, inward rectification, and permeability to K+).(ABSTRACT
TRUNCATED AT 250 WORDS)
