AJP - Lung Cellular and Molecular Physiology, Vol 259, Issue 6 410-L414, Copyright © 1990 by American Physiological Society
Evidence that Ca2(+)-dependent activation of airway epithelia Cl- channels is not dependent on phosphorylation
J. P. Clancy, J. D. McCann and M. J. Welsh
Howard Hughes Medical Institute, Department of Internal Medicine, University of Iowa College of Medicine, Iowa City 52242.
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 125I- 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 microM), to nonspecifically inhibit
kinase activity, blocked cAMP- and PMA-stimulated 125I- efflux but had no
effect on A23187-induced efflux. These results suggest that elevation of
[Ca2+]c does not activate Cl- channels via phosphorylation.
