Calcium-dependent inactivation of inwardly rectifying K+ channel in a tumor mast cell line.
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)
Mukai
M
M
Department of Physiology, Osaka City University Medical School, Japan.
Kyogoku
I
I
Kuno
M
M
D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004594:Electrophysiology; D007700:Kinetics; D015471:Leukemia, Basophilic, Acute / Q000378:metabolism / Q000473:pathology; D008407:Mast Cells / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects* / Q000502:physiology; D014407:Tumor Cells, Cultured
D015221:Potassium Channels; D002118:Calcium