Involvement of calmodulin and protein kinase C in the regulation of K+ transport by carbachol across the rat distal colon

The cholinergic agonist carbachol stimulates the apical H+-K+-ATPase and ap ical as well as basolateral K+ channels in the rat distal colon. The effect of carbachol was tested in the presence of different inhibitors of the Ca2 + signaling pathway in order to characterize the intracellular mechanisms i nvolved. Both carbachol-stimulated Rb+-efflux as well as carbachol-stimulat ed mucosal Rb+-uptake were dependent on the presence of serosal Ca2+. The C a2+-calmodulin antagonist calmidazolium (10(-7) mol l(-1)) inhibited the st imulation of mucosal and serosal Rbf efflux by carbachol. A similar effect had KN-62 (10(-5) mol l(-1)), an inhibitor of the Ca2+-calmodulin-dependent kinase II, suggesting the regulation of basolateral and apical K+ channels by this kinase. Staurosporine (10(-6) mol l(-1)), which potently inhibits protein kinase C, did not alter the effect of carbachol on Rb+ efflux, alth ough the stimulation of apical Rb+ efflux by carbachol seemed to be less pr olonged, indicating that protein kinase C is not involved in the regulation of K+ permeability. In contrast, mucosal Rbf uptake, which is determined b y the ouabain- and vanadate-sensitive K+ transport via the apical H+-K+-ATP ase, was decreased to nearly one third of control values in the presence of calmidazolium. Both calmidazolium and staurosporine, but not KN-62, preven ted the stimulatory action of carbachol on the H+-K+-ATPase, suggesting a s ynergistic control of this ion pump by both Ca2+-calmodulin and protein kin ase C. (C) 1999 Elsevier Science B.V. All rights reserved.