Ca2+-dependent inactivation of a store-operated Ca2+ current in human submandibular gland cells - Role of a staurosporine-sensitive protein kinase and the intracellular Ca2+ pump

Stimulation of human submandibular gland cells with carbachol, inositol tri sphosphate (IP3), thapsigargin, or tert-butylhydroxyquinone induced an inwa rd current that was sensitive to external Ca2+ concentration ([Ca2+](e)) an d was also carried by external Na+ or Ba2+ (in a Ca2+-free medium) with amp litudes in the order Ca2+ > Ba2+ > Na+. All cation currents were blocked by La3+ and Gd3+ but not by Zn2+. The IP3-stimulated current with 10 mu M 3-d eoxy-3-fluoro-D-myo-inositol 1,4,5-triphosphate and 10 mM 1,2-bis(2-aminoph enoxy)ethane-N,N,N',N'-tetraacetic acid in the pipette solution, showed 50% inactivation in <5 min and >5 min with 10 and 1 mM [Ca2+](e), respectively . The Na+ current was not inactivated, whereas the Ba2+ current inactivated at a slower rate. The protein kinase inhibitor, staurosporine, delayed the inactivation and increased the amplitude of the current, whereas the prote in Ser/Thr phosphatase inhibitor, calyculin A, reduced the current. Thapsig argin- and tert-butylhydroxyquinone-stimulated Ca2+ currents inactivated fa ster. Importantly, these agents accelerated the inactivation of the IP3-sti mulated current. The data demonstrate that internal Ca2+ store depletion-ac tivated Ca2+ current (I-SOC) in this salivary cell line is regulated by a C a2+-dependent feedback mechanism involving a staurosporine-sensitive protei n kinase and the intracellular Ca2+ pump. We suggest that the Ca2+ pump mod ulates I-SOC by regulating [Ca2+](i) in the region of Ca2+ influx.