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

Abstract

The cholinergic agonist carbachol stimulates the apical H +–K +–ATPase and apical 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 Ca 2+ signaling pathway in order to characterize the intracellular mechanisms involved. Both carbachol-stimulated Rb +-efflux as well as carbachol-stimulated mucosal Rb +-uptake were dependent on the presence of serosal Ca 2+. The Ca 2+–calmodulin antagonist calmidazolium (10 −7 mol l −1) inhibited the stimulation of mucosal and serosal Rb + efflux by carbachol. A similar effect had KN-62 (10 −5 mol l −1), an inhibitor of the Ca 2+–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, although the stimulation of apical Rb + efflux by carbachol seemed to be less prolonged, indicating that protein kinase C is not involved in the regulation of K + permeability. In contrast, mucosal Rb + uptake, which is determined by the ouabain- and vanadate-sensitive K + transport via the apical H +–K +–ATPase, was decreased to nearly one third of control values in the presence of calmidazolium. Both calmidazolium and staurosporine, but not KN-62, prevented the stimulatory action of carbachol on the H +–K +–ATPase, suggesting a synergistic control of this ion pump by both Ca 2+–calmodulin and protein kinase C.