Different effect of serotonin on intracellular calcium ion dynamics in the smooth muscle cells between rat posterior ciliary artery and vorticose vein

Abstract

5-hydroxytriptamine (5-HT: serotonin) is an important transmitter that causes vessel constriction, although few studies have examined the effect of 5-HT on venous smooth muscles. The intracellular Ca2+ concentration ([Ca2+]i) plays an essential role in stimulus-response coupling in numerous tissue/cells including vascular smooth muscle cells. The present study was performed to examine whether differences between arteries and veins in the response to 5-HT can be detected under confocal microscope with respect to [Ca2+]i dynamics. In posterior ciliary arteries of rats, 5-HT induced a [Ca2+]i increase. The 5-HT-induced responses were caused by both Ca2+ influx and mobilization. Agonist and antagonist experiments revealed that arterial smooth muscles possess 5-HT1a, 1b, 2 (Gprotein- coupled type) and 5-HT3 (ion channel type) receptors, and that 5-HT2 in particular plays a major role in these responses. For vorticose veins, the 5-HT-induced responses were also caused by both Ca2+ influx and mobilization. However, the cAMP dependent pathway (5-HT4-7) was found to be significant in vasocontraction with respect to 5-HT in these vessels. Thus, Ca2+ mobilization was induced by 5-HT2 and 5-HT4-7 in a vessel-dependent manner, whereas Ca2+ influx universally was induced by 5-HT3. These results indicate that the posterior ciliary arteries and vorticose veins in the same tissue might differ greatly in their responses to stimulus.