Role of store-operated calcium entry in imperatorin-induced vasodilatation of rat small mesenteric artery

Store-operated Ca2+ entry (SOCE) has recently been proposed to contribute to Ca2+ influx in vascular smooth muscle cells (VSMCs). Imperatorin is known for its potent vasodilatory effects as a dietary furanocoumarin. The study was designed to examine the hypothesis that SOCE have a functional role in imperatorin-induced vasodilation. Small mesenteric resistance arteries and mesenteric VSMCs were obtained from rats. Isometric tensions of isolated artery rings were measured by a sensitive myograph system. Laser scanning confocal microscopy was used to determine the intracellular Ca2+ concentration of fluo-3-loaded VSMCs. Imperatorin (1–100 μM) relaxed artery rings precontracted by phenylephrine in a concentration-dependent manner. In cultured mesenteric VSMCs, passive store depletion by thapsigargin and active store depletion by phenylephrine both induced Ca2+ influx due to SOCE. Imperatorin didn't inhibit SOCE-mediated increases in cytosolic Ca2+ levels evoked by the emptying of the stores. In isolated artery rings, imperatorin didn't inhibit SOCE-induced contractions due to store depletion. Our results exclude SOCE mechanism of vasodilatation by imperatorin. But imperatorin is partly similar with nifedipine in vasorelaxation effect.