Endothelin-1-evoked arachidonic acid release: A Ca2+-dependent pathway

Endothelins (ET) are potent vasoconstricting peptides with 21 amino acid residues. Endothelin-1 (ET-1) stimulates arachidonic acid (AA) release in human pericardial smooth muscle cells (HPSMC), which is primarily mediated through the ET(A) receptor. Manoalide, an inhibitor for phospholipase A(2), inhibited the ET-1-evoked response by 50% at 1 mu M. RHC-80267, an inhibitor for diacylglycerol lipase, did not have a significant effect. The Ca2+ ionophore A-23187 at 2 mu M greatly stimulated AA release in the presence of extracellular Ca2+. ET-1 (10 nM) evoked a robust Ca2+ response. The intracellular Ca2+ concentration reached a peak after 10 a and gradually decreased to a new plateau level in the presence of extracellular Ca2+. ET-1-evoked AA release closely followed the change in the intracellular Ca2+ concentration. Removal of extracellular Ca2+ or treating cells with 250 mu M bis(2-amino-5-methylphenoxy)ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (MAPTAM; an intracellular Ca2+ chelator) greatly reduced ET-1-stimulated AA release. The protein kinase C (PKC) inhibitors, staurosporine (1 mu M) and chelerythrine chloride (2.5 mu M), inhibited ET-1-evoked AA release by 70%. Phorbol 12-myristate 13-acetate, a PKC activator, potentiated the effect of ET on AA release. The data suggest that the effect of ET on AA release in HPSMC is via phospholipase A(2), which is modulated by Ca2+ and PKC.