Activation of Na+/H+ exchange in cultured fibroblasts: synergism and antagonism between phorbol ester, Ca2+ ionophore, and growth factors.
The effects of phorbol 12-myristate 13-acetate (PMA), a potent activator of protein kinase C, on Na+ influx were investigated in cultured human foreskin fibroblasts (HSWP cells). We report here that in serum-deprived HSWP cells the addition of PMA alone has no significant effect on Na+ influx. However, the addition of PMA to cells whose Na+/H+ exchanger is partially activated with a submaximal dose of the Ca2+ ionophore A23187 leads to a larger stimulation than seen with A23187 alone. These data suggest that although stimulation of protein kinase C is not a sufficient signal to activate the Na+/H+ exchanger in HSWP cells or in another human foreskin line (Jackson fibroblasts) studied, there are some cooperative effects of protein kinase C activation with a rise in Ca2+ to stimulate Na+/H+ exchange. In addition, we found that PMA actually inhibits the mitogen-induced stimulation of Na+ influx in HSWP and Jackson fibroblasts. This observation strengthens the argument that in these cells activation of protein kinase C is not sufficient to activate Na+/H+ exchange and suggests that there is a negative feedback control via protein kinase C that inhibits some signal that is necessary for activating Na+/H+ exchange. However, in contrast to observations in HSWP cells, we were able to activate the Na+/H+ exchanger in mouse 3T3 and human WI-38 cells with PMA alone, suggesting that there is some diversity in the mechanism for activation of Na+/H+ exchange in different types of fibroblasts.
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D004357:Drug Synergism; D006133:Growth Substances / Q000494:pharmacology*; D006801:Humans; D051379:Mice; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
D002352:Carrier Proteins; D006133:Growth Substances; D010704:Phorbols; D017923:Sodium-Hydrogen Exchangers; D000001:Calcimycin; D012964:Sodium; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate