PLATELET-ACTIVATING-FACTOR INDUCED CALCIUM MOBILIZATION AND PHOSPHOINOSITIDE METABOLISM IN CULTURED BOVINE CEREBRAL MICROVASCULAR ENDOTHELIAL-CELLS

Platelet-activating factor (PAF) is a powerful lipid autacoid with a variety of biological activities. More and more evidence suggests that PAF might play an important role in modulation of cerebrovascular system function, particularly during ischemia-induced cerebrovascular damage. However, the mechanisms involved in PAF actions on cerebrovascular or other brain cells are virtually unknown. Therefore, this study was designed to investigate PAF receptor-mediated cellular signal transduction in bovine cerebral microvascular endothelial (CME) cells with the aid of a potent PAF antagonist, WEB 2086. PAF induced an immediate and concentration-dependent increase in [Ca2+](i) with an EC(50) of 4.75 nM. PAF-induced [Ca2+](i) mobilization was inhibited by PAF antagonist WEB 2086, in a dose-dependent manner (IC50 = 15.53 nM). The calcium channel blockers diltiazem (10 mu M) and verapamil (10 mu M) had no effect on the PAF-induced increase in [Ca2+](i), but depletion of Ca2+ from the incubation buffer caused a 45.26% reduction of PAF-induced [Ca2+](i) elevation. PAF stimulated phosphoinositide metabolism in a dose-dependent manner with an EC(50) of 12.4 nM for IP3 formation, which was also inhibited by the PAF antagonist WEB 2086 in a dose-dependent manner with IC50 value of 16.97 nM for IP3 production. These data indicate that bovine CME cells respond to biologically relevant concentrations of PAF and this response involves activation of phospholipase C and increase in [Ca2+](i) via specific PAF receptors. Our results may contribute to further understanding of the mechanism behind PAF actions on cerebrovascular cells.