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 vascular smooth muscle. This study aimed to clarify this question by conducting isometric tension experiments and Ca-45(2+) flux measurements in endothelium-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 abolished with high concentrations. Ca2+ store depletion with a maximum dose of caffeine in Ca2+-free solution further reduced the contraction by subsequent thiopental. Ca2+ store depletion with thapsigargin completely abolished contraction by thiopental. Ca-45(2+) influx experiment in the presence of verapamil showed that thiopental could not induce any Ca2+ influx with or without phenylephrine prestimulation The Ca-45(2+) efflux experiment showed more evidence of thiopental-induced Ca2+ release, which was abolished by thapsigargin. In conclusion, thiopental induces contraction in rat aortic smooth muscle by releasing Ca2+ from the sarcoplasmic reticulum without Ca2+ influx.