Thiopental induces contraction of rat aortic smooth muscle through Ca2+ release from the sarcoplasmic reticulum

Little is known about the mechanism of thiopental-induced contraction in va scular smooth muscle. This study aimed to clarify this question by conducti ng isometric tension experiments and Ca-45(2+) flux measurements in endothe lium-denuded rat aortic rings. Thiopental induced a concentration-dependent contraction under basal tension. This contraction was enhanced when rings were precontracted with phenylephrine in the presence of verapamil. In Ca2-free solution, thiopental-induced contraction was reduced but not abolishe d with high concentrations. Ca2+ store depletion with a maximum dose of caf feine in Ca2+-free solution further reduced the contraction by subsequent t hiopental. Ca2+ store depletion with thapsigargin completely abolished cont raction by thiopental. Ca-45(2+) influx experiment in the presence of verap amil showed that thiopental could not induce any Ca2+ influx with or withou t phenylephrine prestimulation The Ca-45(2+) efflux experiment showed more evidence of thiopental-induced Ca2+ release, which was abolished by thapsig argin. In conclusion, thiopental induces contraction in rat aortic smooth m uscle by releasing Ca2+ from the sarcoplasmic reticulum without Ca2+ influx .