REGULATION OF INTRACELLULAR PH BY PHOSPHOLIPASE-A2 AND PROTEIN-KINASE-C UPON NEUTROPHIL ADHESION TO SOLID SUBSTRATA

Adhesion to solid substrata has been shown to increase intracellular p H (pH(i)) of fibroblasts and of other cells (FEBS Lett, (1988) 234, 44 9-450; Proc, Natl, Acad, Sci, USA (1989) 86, 4525-4529; J. Biol, Chem, (1990) 265, 1327-1332; Exp, Cell Res, (1992) 200, 211-214; FEES Lett, (1995) 374, 17-20), We have found that the inhibitors of PLA2, 4-brom ophenacyl bromide and manoalide, completely blocked the increase of pH (i) and spreading of neutrophils upon adhesion to solid substrata, Inh ibition of phospholipase C with neomycin or removal of extracellular C a2+ affects neither neutrophil spreading nor their pH(i), Inhibition o f PKC with H-7 or staurosporin increased pH(i), PMA, an activator of P KC, dramatically decreased pH(i) but did not impair the spreading of n eutrophils. The effect of arachidonic acid, a product of PLA2 activity , on neutrophil pH(i) and spreading was similar to that of PMA, H-7, a n inhibitor of PKC, partially blocked the effect of arachidonic acid ( AA) on pH(i). BW755C, an inhibitor of AA metabolism by cyclooxygenase or lipoxygenase, affected neither the pH(i) nor cell spreading, We pro pose that the increase of pH(i) upon neutrophil adhesion is mediated b y PLA2 activity, while PKC decreased pH(i). AA produced by PLA2 activa tes PKC, thus forming a feedback regulation of pH(i).