| Abstract: | In quiescent cultures of Swiss 3T3 cells, prostaglandin E1 (PGE1) known to elevate cAMP increased rapidly cytoplasmic free Ca2+ concentration (Ca2+]i) as measured with the fluorescent Ca2+ indicator quin2. The primary source of the PGE1-induced elevation of Ca2+]i was extracellular. Pretreatment of the cells with various doses of 12-O-tetradecanoylphorbol-13-acetate (TPA), a potent protein kinase C-activating phorbol ester, inhibited the PGE1-induced elevation of Ca2+]i in a dose-dependent manner. Inversely, TPA enhanced slightly the PGE1-induced increase of cAMP. TPA alone did not affect the basal level of Ca2+]i or cAMP in the absence of PGE1. The inhibitory action of TPA on the PGE1-induced elevation of Ca2+]i was mimicked by other protein kinase C-activating agents such as phorbol 12,13-dibutyrate and 1-oleoyl-2-acetylglycerol. 4 alpha-Phorbol 12,13-didecanoate known to be inactive for protein kinase C was ineffective in this capacity. Prolonged treatment of the cells with phorbol 12,13-dibutyrate resulted in the down-regulation and disappearance of protein kinase C. In these protein kinase C-deficient cells, PGE1 still elevated Ca2+]i to the same extent as that in the control cells, but TPA did not inhibit the PGE1-induced elevation of Ca2+]i. These results strongly suggest that protein kinase C serves as an inhibitor for PGE1-induced Ca2+ influx in Swiss 3T3 cells. |
