Parotid Acini: Comparison of the Roles of Cytosolic Ca2+ and Protein Kinase C.

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Carbachol (CCh) stimulated K+ release from rat parotid acini. Treatment with the intracellular Ca2+ antagonist 8-(N, N-diethylamino)octyl-3, 4, 5-trimethoxybenzoate (TMB-8) or the intracellular Ca2+ chelator 1, 2-bis(O-aminophenoxy)ethane-N, N, N'', N''-tetraacetic acid (BAPTA) strongly suppressed the CCh-induced K+ release. Combined addition of the Ca2+ ionophore ionomycin and the microsomal Ca2+-ATPase inhibitor thapsigargin caused a rapid increase in cytosolic Ca2+ concentration ([Ca2+]i) and resulted in a marked release of K+. In the absence of extracellular Ca2+, CCh or a combination of ionomycin and thapsigargin caused a transient release of K+ which correlated well with the transient change in [Ca2+]i. On the other hand, phorbol 12-myristate 13-acetate (PMA) did not potentiate the CCh-induced K+ release, although the CCh-induced amylase release was significantly enhanced in the presence of PMA. Staurosporine, a protein kinase C-inhibitor, did not inhibit the CCh-induced K+ release, which was in contrast with its inhibitory effect on amylase release. These results suggest that the K+ release from rat parotid acini induced by CCh stimulation is mediated by a rapid increase in [Ca2+]i but is not associated with activation of protein kinase C. This signal pathway is different from that for amylase release where activation of protein kinase C plays an important role.
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