Eicosapentaenoic acid inhibits vasopressin-activated Ca2+ influx and cell proliferation in rat aortic smooth muscle cell lines

The purpose of this study was to clarify how eicosapentaenoic acid (EPA), an <(omega)over bar>-3 polyunsaturated fatty acid, modulates the vascular action of vasopressin in rat aortic smooth muscle cell lines. The effects of EPA on Ca2+ mobilization and DNA synthesis elicited by vasopressin were investigated and compared to those of Ca2+ channel blocking agents, by means of Ca2+ measurements and the incorporation of [H-3]thymidine. Patch-clamp techniques were also employed. Vasopressin (100 nM) elicited an initial peak of intracellular Ca2+ ([Ca2+]), followed by a sustained phase due to Ca2+ entry, Nifedipine or nicardipine (1 mu M), a potent L-type Ca2+ channel blocker, partly inhibited the sustained phase, but La3+ completely abolished it. EPA (10 mu M) also inhibited it even in the presence of nicardipine. Under voltage-clamp conditions with CsCl-internal solution, depolarizing pulses positive to -30 mV from a holding potential of -40 mV elicited a slow inward current. The inward current was blocked by La3+, nicardipine, and nifedipine (1 mu M), suggesting that the inward current mainly consisted of the voltage-dependent L-type Ca2+ channel (I-Ca.L). EPA (1-30 mu M) also inhibited I-Ca.L in a concentration-dependent manner. The inhibitory effect of EPA was observed at concentrations higher than 1 mu M, and its half-maximal inhibitory concentration (IC50) was 7.6 mu M Vasopressin induced a long-lasting inward current at a holding potential of -40 mV, The vasopressin-induced current was considered as a non-selective cation current (I-cat) with a reversal potential of approximately +0 mV, Both nifedipine and nicardipine (10 mu M) failed to inhibit it significantly, but La3+ completely abolished I-cat. EPA also inhibited vasopressin-induced IC50 in a concentration-dependent manner; its IC50 value was 5.9 mu M. Vasopressin (100 nM) stimulated [H-3]thymidine incorporation. Exclusion of extracellular Ca2+ with EGTA or La3+ markedly inhibited it. EPA (3-30 mu M) also inhibited the incorporation induced by vasopressin, while nifedipine and nicardipine (1 mu M) only partly inhibited it. These results suggested that EPA, unlike nifedipine and nicardipine, inhibited vasopressin-induced Ca2+-entry and proliferation in rat vascular smooth muscle cells, where the inhibitory effects of EPA on I-cat as well as I-Ca.L might be involved. Thus, EPA would exert hypotensive and antiatherosclerotic effects. (C) 1999 Elsevier Science B.V. All rights reserved.