Modulation of Ca2+ mobilization by protein kinase C in the submandibular duct cell line A253

The expression of protein kinase C (PKC) isoforms and the modulation of Ca2 + mobilization by PKC were investigated in the human submandibular duct cel l line A253. Three new PKC (nPKC) isoforms (delta, epsilon, and theta) and one atypical PKC (aPKC) isoform (lambda) are expressed in this cell line. N o classical PKC (cPKC) isoforms were present. The effects of the PKC activa tor phorbol 12-myristate-13-acetate (PMA) and of the PKC inhibitors calphos tin C (CC) and bisindolymaleimide I (BSM) on inositol 1,4,5-trisphosphate ( IP3) and Ca2+ responses to ATP and to thapsigargin (TG) were investigated. Pre-exposure to PMA inhibited IP3 formation, Ca2+ release and Ca2+ influx i n response to ATP. Pre-exposure to CC or BSM slightly enhanced IP3 formatio n but inhibited the Ca2+ release and the Ca2+ influx induced by ATP. In con trast, pre-exposure to PMA did not modify the Ca2+ release induced by TG, b ut reduced the influx of Ca2+ seen in the presence of this Ca2+-ATPase inhi bitor. These results suggest that PKC modulates elements of the IP3/Ca2+ si gnal transduction pathway in A253 cells by (1) inhibiting phosphatidylinosi tol turnover and altering the sensitivity of the Ca2+ channels to IP3, (2) altering the activity, the sensitivity to inhibitors, or the distribution o f the TG-sensitive Ca2+ ATPase, and (3) modulating Ca2+ entry pathways.