CHANGES IN CA2- THE ROLE OF PROTEIN-KINASE-C IN REGULATION OF CA2+ ENTRY( CONCENTRATION IN PHORBOL ESTER AND THAPSIGARGIN TREATED GLIOMA C6CELLS )

Glioma C6 cells treated with 12-O-tetradecanoyl-phorbol-13-acetate, TP A (10 nM and 100 nM) manifested slow increase in intracellular calcium concentration ([Ca2+]i), dependent upon both Ca2+ release from intrac ellular stores and Ca2+ entry, and ranging from 50 to 500 nM in differ ent cells. The effect of TPA was abolished by the down-regulation proc edure and by protein kinase C inhibitors, such as staurosporine (100 n M), suramin (100 mu M), and sphingosine (100 mu M), pointing to a role of protein kinase C (PKC) in this process. On the other hand, thapsig argin (100 nM), a selective inhibitor of the endoplasmic reticulum Ca2 +-ATPase, produced a rapid increase in [Ca2+]i (up to 800 nM). This in crease consisted of a transient initial phase followed by sustained el evation in [Ca2+]i, typical of Ca2+ release from intracellular stores and of Ca2+ entry, respectively, However, when the cells were exposed to TPA (100 nM) prior to thapsigargin (100 nM), then thapsigargin prod uced only a [Ca2+]i. We suggest that TPA, a PKC activator, affects tha psigargin-induced Ca2+ entry, probably by PKC-mediated changes in cyto skeleton structures.