Modulation of large conductance calcium-activated K+ channel by membrane-delimited protein kinase and phosphatase activities.

Large conductance Ca(2+)-activated K+ channel was identified and studied in excised inside-out membrane patches of freshly dispersed smooth muscle cells from rabbit gastric antrum. The current-voltage relationship of the single channel was linear from -80 to +80 mV of pipette voltage in which single channel conductance was 249 +/- 17.8 pS (n = 19) in symmetrical concentration of K+ (145 mM) across the patch. Activity of the channel (NPo) depended not only on cytoplasmic calcium concentration but also on membrane potential. MgATP increased NPo in a dose-dependent manner and Mg2+ was prerequisite for the effect. Okadaic acid (100 nM), inhibitor of protein phosphatases, increased NPo further in the presence of MgATP. Therefore, it would be concluded that activity of the calcium-activated K+ channel in gastric smooth muscle cells was controlled by phosphorylation state of the channel protein and the state is further modulated by membrane-delimited protein kinase and protein phosphatase activities.