INVOLVEMENT OF A GUANINE-NUCLEOTIDE-BINDING PROTEIN-MEDIATED MECHANISM IN THE ENHANCEMENT OF ARACHIDONIC-ACID LIBERATION BY PHORBOL 12-MYRISTATE 13-ACETATE AND CA-2+ IN SAPONIN-PERMEABILIZED PLATELETS

A mechanism by which protein kinase C potentiates arachidonic acid (AA) liberation in rabbit platelets was examined using [3H]AA-labeled, saponin (7 μg/ml)-permeabilized rabbit platelets. Pretreatment of the [3H]AA-labeled platelets with 4β-phorbol 12-myristate 13-acetate (PMA, 10-40 nM) or 1,2-dioctanoylglycerol (DOG, 20 μM) enhanced [3H]AA liberation induced by an addition of Ca2+ (1 mM) after cell permeabilization, whereas 4α-phorbol 12,13-didecanoate (80 nM) did not exert such an effect. The potentiating effects of PMA and DOG were inhibited by staurosporine (200 nM). PMA (40 nM) also potentiated [3H]AA liberation induced by guanosine 5′-[γ-thio]triphosphate (GTPγS, 100 μM), 5′-guanylyl imidodiphosphate (200 μM) or NaF (20 mM) plus AlCl3 (10 μM) in the presence of Ca2+ (100 μM). The enhancement by PMA of the GTPγS-induced AA liberation was also inhibited by staurosporine (200 nM). Furthermore, guanosine 5′-[β-thio]diphosphate (GDPβS, 0.5-2 mM) suppressed the PMA (40 nM)- and DOG (20 μM)-enhanced, Ca2+ (1 mM)-dependent [3H]AA liberation. This inhibitory effect of GDPβS was reversed by a further addition of GTPγS (200 μM). However, pertussis toxin (0.2-1 μg/ml) had no effect on the PMA-enhanced [3H]AA liberation. These results indicate a possibility that protein kinase C may potentiate AA liberation through a guanine-nucleotide-binding protein-mediated mechanism in saponin-permeabilized rabbit platelets. © 1990.