MODULATION BY PROTEIN-KINASE-C OF ARACHIDONIC-ACID RELEASE FROM PERMEABILIZED MYOMETRIAL CELLS OF GUINEA-PIG UTERUS

The effects of protein kinase C activation on phospholipase A2 and pho spholipase C activity in permeabilised cultured myometrial cells from guinea pig uterus have been studied. Phospholipase A2 activity was fol lowed by measurement of [H-3]arachidonic acid release from [H-3]arachi donic acid-prelabelled membrane lipids. [H-3]Arachidonic acid release was stimulated by Ca2+ at 1-10 muM and by GTPgammaS at 1 muM to 1 mM i n the presence of 10 muM Ca2+. The activation by calcium was enhanced 89.5 +/- 12.7% (P<0.01) in the presence of 1 muM phorbol 12-myristate 13-acetate (PMA) and that by 1 muM GTPgammaS by 65.4 +/- 4.4% (P<0.001 ). The PMA enhancement of arachidonic acid release was completely bloc ked by 3 muM staurosporine. Phospholipase C activation was followed by measurement of [H-3]inositol polyphosphate production from [H-3]inosi tol-prelabelled membrane lipids. This was stimulated by Ca2+ at 0.1 an d 10 muM and by 1 and 50 muM GTPgammaS. PMA at 1 muM caused a consiste nt reduction in the extent of Ca2+ and GTPgammaS-stimulated inositol p olyphosphate production and 3 muM reversed the inhibitory action of PM A. The data are consistent with arachidonic acid release in permeabili sed myometrial cells from guinea pigs reflecting in large part phospho lipase A2 activation and with that pathway being stimulated by protein kinase C activation. They are also consistent with protein kinase C a ctivation causing reduction in phospholipase C pathways in uterine myo cytes, at least as measured by inositol polyphosphate release.