ROLE FOR PROTEIN-KINASE IN CA2-DEPENDENT FEEDBACK MODULATION OF DIVALENT-CATION INFLUX IN INTERNAL-CA2+-STORE-DEPLETED RAT PAROTID-GLAND CELLS()

Divalent cation (Ca2+ and Mn2+) influx, stimulated by internal Ca2+ st ore depletion, into rat parotid acinar cells is inhibited by condition s which increase protein phosphorylation [T. Sakai and I.S. Ambudkar ( 1996) Am J Physiol 271:C284-C294]. The present study examines the invo lvement of this protein phosphorylation and Ca2+ in the store-dependen t inactivation of divalent cation entry. Internal Ca2+ store depletion , achieved by incubation (30 min) of cells in nominally Ca2+-free medi um containing either carbachol or thapsigargin, stimulated Ca2+. and M n2+. influx into cells. In either case, inclusion of 1.5 mM Ca2+ for t he last 5 min of incubation resulted in a decrease in Ca2+ (33-41%) an d Mn2+ (50%) influx, which could not be accounted for by internal Ca2 store refill. The inhibition was prevented when internal-store-deplet ed cells were treated (prior to incubation with Ca2+) with either stau rosporine or K-252a, but not with H-7 or KN-93. Refilling of internal Ca2+ store(s) in carbachol-treated cells (incubation with Ca(2+)atropi ne) induced complete inhibition of divalent cation influx, which was n ot prevented by treatment with protein kinase inhibitors. These data s uggest the staurosporine-sensitive (and K-252a-sensitive) protein phos phorylation is not involved in Ca2+-store-refilling-dependent inactiva tion of Ca2+ influx but mediates a Ca2+-dependent feedback modulation of divalent cation influx in rat parotid gland acinar cells.