Effects of Bradykinin on the Regulatory Mechanism of PGI2 Synthesis in Human Vascular Endothelial Cells with Reference to the Intracellular Ca2+ Kinetics and mRNA Expression of Cytosolic Phospholipase A2 (cPLA2) and Prostaglandin H2 Synthase-1 (PGHS-1)

We investigated the effects of bradykinin (BK) on the regulatory mechanism of PGI2 synthesis in endothelial cells with reference to intracellular Ca2+ kinetics, mRNA expression of cytosolic phospholipase A2 (cPLA2) and prostaglandin H2 synthase-1 (PGHS-1).PGI2 generation increased with BK stimulation in a time dependent manner for 180 minutes. In the early phase of BK stimulation, intracellular Ca2+ ([Ca2+]i) concentration was increased by the influx of extracellular Ca2+ and a release from the Ca2+ storage site. However the increase of [Ca2+] i was observed for only 2 minutes.cPLA2 mRNA expression was 87 amol/μg RNA at rest. The additon of BK produced 746amol/μg RNA at 15 minutes. After pretreatment with cycloheximide, cPLA mRNA was superinduced. PGHS-1 mRNA expression was 562 amol/μg RNA at rest. The additon ofBK produced 10608 amol/μg RNA at 180 minutes. After pretreatment with cycloheximide, PGHS-1 mRNA expression was inhibited.These results indicate that in the early phase of BK stimulation, [Ca2+]i activates cPLA2, and cPLA2 is considered to increase PGI2 generation. After 2 minutes, the increase of cPLA2 and PGHS-1 mRNA with BK stimulation seems to lead to an increase in these enzymes, but the time courses of these mRNA expressions were not the same.It is suggested that BK induced PGI2 generation depends not only on the increase of [Ca2+]i but also on the mRNA of cPLA2 and PGHS-1.

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