ENDOTHELIN-1 STIMULATES CONTRACTION OF RAT GLOMERULAR MESANGIAL CELLS AND POTENTIATES BETA-ADRENERGIC-MEDIATED CYCLIC ADENOSINE-MONOPHOSPHATE ACCUMULATION

The newly isolated peptide, endothelin-1 (ET-1), is a potent pressor agent that reduces GFR and the glomerular ultrafiltration coefficient. Recent evidence demonstrates that ET-1 mobilizes intracellular Ca2+ ([Ca2+](i)) in glomerular mesangial cells by activating the phosphoinositide cascade. The present experiments were designed to examine whether ET-1 stimulates mesangial cell contraction and regulates the synthesis of PGE2 and cAMP, which dampen vasoconstrictor-induced mesangial contraction. ET-1 (≥1 nM) reduced the cross-sectional area of rat mesangial cells cultured on three-dimensional gels of collagen type I. ET-1 also caused complex rearrangements of F-actin microfilaments consistent with a motile response. Contraction in response to ET-1 occurred only at concentrations that activate phospholipase C, and contraction was unaffected by blockade of dihydropyridine-sensitive Ca2+ channels. Elevation of [Ca2+](i) with ionomycin, to equivalent concentrations of [Ca2+](i) achieved with ET-1, also reduced mesangial cell cross-sectional area. ET-1 (0.1 μM) also evoked [3H]arachidonate release and a fivefold increase in PGE3 synthesis as well as increased synthesis of PGF(2α) and small changes of TXB2. ET-1 caused a minor increase in intracellular cAMP accumulation only in the presence of 3-isobutyl-1-methylxanthine. ET-1 also amplified cAMP production in response to isoproterenol. TPA and ionomycin, alone and in combination, failed to mimic the potentiating effect of ET-1; however, indomethacin blocked ET-1-induced potentiation of isoproterenol-stimulated cAMP, which was restored by addition of exogenous 10 nM PGE2. Thus the present data demonstrate that ET-1 stimulates mesangial cell contraction via pharmacomechanical coupling and activates phospholipase A2 to produce PGE2, PGF(2α), and TXB2. ET-1 also amplified β adrenergic-stimulated cAMP accumulation by a PGE2-dependent mechanism.