INTRACELLULAR ACIDIFICATION MEDIATES THE PROLIFERATIVE RESPONSE OF PC12 CELLS INDUCED BY POTASSIUM FERRICYANIDE AND INVOLVES MAP KINASE ACTIVATION

Potassium ferricyanide is known to elicit cell growth and mitogenesis in various cells by stimulating a transplasma membrane electron-transp ort system. When serum-starved PC12 cells were treated with potassium ferricyanide, stimulation of mitogenesis was evidenced by enhanced DNA synthesis, as well as by increased cell numbers. Intracellular pH (pH (i)) of PC12 cells was measured at 37 degrees C by microfluorimetric a nalysis of 2',7'-bis-(2-carboxyethyl)-5(and -6)-carboxyfluorescein (BC ECF). The resting pH(i) of unstimulated cells was 7.52 (external pH 7. 40). Addition of potassium ferricyanide (100 mu M) decreased pH(i) by about 0.25 pH units. Lowering pH(i) to a similar extent, either by dec reasing external pH (pH(o)) or by adding a weak acid, also elicited a mitogenic response, indicating that intracellular acidification by its elf has growth factor-mimicking, mitogenic effects. Nerve growth facto r (NGF) or basic fibroblast growth factor (bFGP) triggered proliferati on without changes in pH(i). The mitogenic treatments eliciting intrac ellular acidification did not activate protein kinase C (PKC) but stim ulated the p42/p44 mitogen-activated protein (MAP) kinase. Our results indicate that 2 distinct mitogenic: pathways are active in PC12 cells : the first is independent of pH(i) and involves activation of the PKC pathway and the second requires a permissive pH(i) value around 7.25 and involves activation of the p42/p44 MAP kinase pathway. (C) 1996 Wi ley-Liss, Inc.