Modulation by protein kinase C of arachidonic acid release from permeabilised myometrial cells of guinea pig uterus.

: The effects of protein kinase C activation on phospholipase A2 and phospholipase C activity in permeabilised cultured myometrial cells from guinea pig uterus have been studied. Phospholipase A2 activity was followed by measurement of [3H]arachidonic acid release from [3H]arachidonic acid-prelabelled membrane lipids. [3H]Arachidonic acid release was stimulated by Ca2+ at 1-10 microM and by GTP gamma S at 1 microM to 1 mM in the presence of 10 microM Ca2+. The activation by calcium was enhanced 89.5 +/- 12.7% (P < 0.01) in the presence of 1 microM phorbol 12-myristate 13-acetate (PMA) and that by 1 microM GTP gamma S by 65.4 +/- 4.4% (P < 0.001). The PMA enhancement of arachidonic acid release was completely blocked by 3 microM staurosporine. Phospholipase C activation was followed by measurement of [3H]inositol polyphosphate production from [3H]inositol-prelabelled membrane lipids. This was stimulated by Ca2+ at 0.1 and 10 microM and by 1 and 50 microM GTP gamma S. PMA at 1 microM caused a consistent reduction in the extent of Ca2+ and GTP gamma S-stimulated inositol polyphosphate production and 3 microM reversed the inhibitory action of PMA. The data are consistent with arachidonic acid release in permeabilised myometrial cells from guinea pigs reflecting in large part phospholipase A2 activation and with that pathway being stimulated by protein kinase C activation. They are also consistent with protein kinase C activation causing reduction in phospholipase C pathways in uterine myocytes, at least as measured by inositol polyphosphate release.