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), a n <(omega)over bar>-3 polyunsaturated fatty acid, modulates the vascular ac tion of vasopressin in rat aortic smooth muscle cell lines. The effects of EPA on Ca2+ mobilization and DNA synthesis elicited by vasopressin were inv estigated and compared to those of Ca2+ channel blocking agents, by means o f Ca2+ measurements and the incorporation of [H-3]thymidine. Patch-clamp te chniques were also employed. Vasopressin (100 nM) elicited an initial peak of intracellular Ca2+ ([Ca2+]), followed by a sustained phase due to Ca2+ e ntry, Nifedipine or nicardipine (1 mu M), a potent L-type Ca2+ channel bloc ker, partly inhibited the sustained phase, but La3+ completely abolished it . EPA (10 mu M) also inhibited it even in the presence of nicardipine. Unde r voltage-clamp conditions with CsCl-internal solution, depolarizing pulses positive to -30 mV from a holding potential of -40 mV elicited a slow inwa rd current. The inward current was blocked by La3+, nicardipine, and nifedi pine (1 mu M), suggesting that the inward current mainly consisted of the v oltage-dependent L-type Ca2+ channel (I-Ca.L). EPA (1-30 mu M) also inhibit ed 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 in hibitory concentration (IC50) was 7.6 mu M Vasopressin induced a long-lasti ng 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 re versal potential of approximately +0 mV, Both nifedipine and nicardipine (1 0 mu M) failed to inhibit it significantly, but La3+ completely abolished I -cat. EPA also inhibited vasopressin-induced IC50 in a concentration-depend ent manner; its IC50 value was 5.9 mu M. Vasopressin (100 nM) stimulated [H -3]thymidine incorporation. Exclusion of extracellular Ca2+ with EGTA or La 3+ markedly inhibited it. EPA (3-30 mu M) also inhibited the incorporation induced by vasopressin, while nifedipine and nicardipine (1 mu M) only part ly inhibited it. These results suggested that EPA, unlike nifedipine and ni cardipine, inhibited vasopressin-induced Ca2+-entry and proliferation in ra t vascular smooth muscle cells, where the inhibitory effects of EPA on I-ca t as well as I-Ca.L might be involved. Thus, EPA would exert hypotensive an d antiatherosclerotic effects. (C) 1999 Elsevier Science B.V. All rights re served.