Characteristics of collagen-induced Ca2+mobilization in bovine platelets

Abstract

We characterized the collagen-induced increase in cytosolic Ca2+([Ca2+]i) of bovine platelets loaded with the Ca2+indicator Fura-PE3/AM. Collagen (10 μg/ml)-induced increase in [Ca2+]iwas only partially inhibited by aspirin, a cyclooxygenase inhibitor, or adenosine 3′-phosphate 5′-phosphosulfate (A3P5PS, a P2Y1receptor antagonist), while in human platelets it was almost completely suppressed by aspirin. Collagen-induced increase in [Ca2+]iof bovine platelets was inhibited by U73122 (0.3–5 μM), a phospholipase C inhibitor. Collagen (10 μg/ml) increased production of inositol 1,4,5-trisphosphate, which was prevented by pretreatment with U73122 (5 μM). Collagen (10 μg/ml) accelerated Mn2+entry, since the rate of Fura-PE3 quenching by Mn2+was enhanced by 13-fold following stimulation with collagen. U73122 inhibited the acceleration of Mn2+entry induced by collagen. PGE1(2.5 μM) partially inhibited the collagen (50 μg/ml)-induced increase in [Ca2+]iin bovine platelets but not in human platelets. The data suggest that collagen-induced Ca2+mobilization in bovine platelets is mediated by phospholipase C. The Ca2+mobilization in bovine platelets is different from that in human ones as to the dependency on arachidonic acid metabolites and sensitivity to PGE1.