Phospholipase C activation by prostaglandins and thromboxane A2 in cultured mesangial cells

Phospholipase C activation by prostaglandins (PG) and thromboxane A2 (TxA2) was studied in cultured rat and human glomerular mesangial cells, measuring accumulation of radiolabeled inositol phosphates and cytosolic free calcium ([Ca2+]i) with the fluorescent intracellular probe fura-2. Prostaglandin F2 alpha (PGF2 alpha) and TxA2 were found to be the major eicosanoids active on this signaling pathway in rat and human cells, respectively, whereas other PG had lesser or no effects. PGF2 alpha and TxA2 rapidly induced accumulation of inositol trisphosphate accompanied by a simultaneous transient rise of [Ca2+]i, followed by sustained elevation or, in human cells, by a distinct second increase of [Ca2+]i within 45 s. A minor initial accumulation of inositol monophosphate was followed by marked elevation greater than 5 min after the early responses. Responses to different eicosanoids were mediated by separate receptors, functionally characterized using receptor antagonists or heterologous desensitization during sequential applications. Protein kinase C activation by serum and phorbol esters potently inhibited inositol phosphate accumulation and/or [Ca2+]i transients, indicating a pathway for a negative feedback on PG-evoked intracellular signals. We conclude that receptor-mediated phospholipase C activation underlies the biological effects of certain eicosanoids on the glomerular mesangium.