EVIDENCE THAT CA-2+-DEPENDENT ACTIVATION OF AIRWAY EPITHELIA CL- CHANNELS IS NOT DEPENDENT ON PHOSPHORYLATION

Previous studies have shown that an increase in the cytosolic Ca2+ concentration (]Ca2+[c) activates Cl- channels in airway epithelia but that the effect is indirect. Because adenosine 3',5'-cyclic monophosphate (cAMP) and phorbol myristate acetate (PMA) activate Cl- channels via phosphorylation by cAMP-dependent protein kinase and protein kinase C, respectively, we asked whether Ca2+ -dependent Cl- channel activation is phosphorylation dependent. We measured I-125- efflux as an assay of Cl- channel activation in the intact cell. We found that depletion of cellular ATP prevented cAMP- and PMA-induced activation but did not alter activation produced by the Ca2+ ionophore A23187. Moreover, addition of high concentrations of staurosporine (5-mu-M), to nonspecifically inhibit kinase activity, blocked cAMP- and PMA-stimulated I-125- efflux but had no effect on A23187-induced efflux. These results suggest that elevation of ]Ca2+[c does not activate Cl- channels via phosphorylation.