title: Phorbol ester and diacylglycerol mimic growth factors in raising cytoplasmic pH.
abstract: There is now good evidence that cytoplasmic pH (pHi) may have an important role in the metabolic activation of quiescent cells. In particular, growth stimulation of mammalian fibroblasts leads to a rapid increase in pHi (refs 3-6), due to activation of a Na+/H+ exchanger in the plasma membrane, and this alkalinization is necessary for the initiation of DNA synthesis. However, the mechanism by which mitogens activate the Na+/H+ exchanger to raise pHi is not known, although an increase in cytoplasmic free Ca2+ ([Ca2+]i) has been postulated as the primary trigger. We now present data suggesting that the Na+/H+ exchanger is set in motion through protein kinase C, a phospholipid- and Ca2+-dependent enzyme normally activated by diacylglycerol produced from inositol phospholipids in response to external stimuli. Using newly developed pH microelectrodes and fluorimetric techniques, we show that a tumour promoting phorbol ester and synthetic diacylglycerol, both potent activators of kinase C (refs 12-15), mimic the action of mitogens in rapidly elevating pHi in different cell types. Furthermore, we demonstrate that, contrary to previous views, an early rise in [Ca2+]i is not essential for the activation of Na+/H+ exchange and the resultant increase in pHi. Finally, we suggest that an alkaline pHi shift, mediated by Na+/H+ exchange, may be a common signal in the action of those hormones which elicit the breakdown of inositol phospholipids.
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D002352:Carrier Proteins / Q000502:physiology; D002478:Cells, Cultured; D004075:Diglycerides / Q000494:pharmacology*; D005989:Glycerides / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D051379:Mice; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C; D011494:Protein Kinases / Q000502:physiology; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D002352:Carrier Proteins; D004075:Diglycerides; D005989:Glycerides; D010704:Phorbols; D017923:Sodium-Hydrogen Exchangers; D011494:Protein Kinases; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium