Platelet-derived growth factor (PDGF) and other agents that activate protein kinase C (PKC) rapidly alter cytosolic pH (pHJ and intracellular free calcium (Ca' +I,) in BALBk-3T3 fibroblasts. To define whether changes in pH, or [Ca++], are linked to PDGF-stimulated mitogenesis, these parameters were assessed in control and PKC depleted fibroblasts. PDGF addition to BALBk-3T3 fibroblasts resulted in transient acidification of the cytoplasm followed by prolonged cytosolic alkalinization. Exposure of cells to 12-tetradecanoy1phorbol-13-acetate (TPA), a phorbol ester that activates PKC, resulted in cytosolic alkalinization without prior acidification. Overnight incubation with 600 n M TPA decreased the total cel I PKC histone phosphorylating activity in BALBlc-3T3 fibroblasts by >go%. In PKC-deficient fibroblasts, TPA, and PDGF-induced alkalinization was abolished. In addition, the transient drop in pH, seen initially in control cells treated with PDGF is sustained to the point where pHi is fully 0.6-0.7 p H units below control cell values for up to 30 minutes.
PDGF increased [Ca++], threefold; this transient rise in [ C a + + l i was only minimally affected (<15%) by lowering of the extracellular calcium level with ethylene glycol bis(b-aminoethyl ether)O N,N,N' tetraacetic acid (EGTA) or blocking calcium influx with CoC12. In contrast, 8-(diethylamine)-octyl-3,4,5trimethoxybenzoate (TMB-8), an agent thought to inhibit calcium release from intracellular stores, substantially inhibited the rise in [Ca++], caused by PDGF. TPA and 1 -oleoyl-2-acetylglycerol (OAG) increased [ C a + + ] , but in contrast to PDGF this effect was blocked by pretreatment of cells with EGTA or CoCI,. In PKC-deficient fibroblasts, PDGF still increased [Ca+ '1, and stimulated DNA synthesis as effectively as in controls. TPA and OAG however, no longer increased [Ca+ +I,. The continued ability of PDGF to stimulate DNA synthesis in the face of sustained acidification and the absence of PKC activity suggests that cytosolic alkalinization and PKC activation are not essential for PDGF-induced competence in BALBlc-3T3 fibroblasts.