Thiopental induces contraction of rat aortic smooth muscle through Ca(2+) 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 (45)Ca(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 Ca(2+)-free solution, thiopental-induced contraction was reduced but not abolished with high concentrations. Ca(2+) store depletion with a maximum dose of caffeine in Ca(2+)-free solution further reduced the contraction by subsequent thiopental. Ca(2+) store depletion with thapsigargin completely abolished contraction by thiopental. (45)Ca(2+) influx experiment in the presence of verapamil showed that thiopental could not induce any Ca(2+) influx with or without phenylephrine prestimulation. The (45)Ca(2+) efflux experiment showed more evidence of thiopental-induced Ca(2+) release, which was abolished by thapsigargin. In conclusion, thiopental induces contraction in rat aortic smooth muscle by releasing Ca(2+) from the sarcoplasmic reticulum without Ca(2+) influx.


CONCLUSIONS
This is the first study providing evidence that thiopental-induced vascular contraction is caused by Ca(2+) release from the sarcoplasmic reticulum of the smooth muscle.
Mousa
W F
WF
Department of Anesthesia, Kyoto University Hospital, Japan.
Enoki
T
T
Fukuda
K
K
D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects* / Q000502:physiology; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D006993:Hypnotics and Sedatives / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*; D019284:Thapsigargin / Q000494:pharmacology; D013874:Thiopental / Q000494:pharmacology*; D014661:Vasoconstriction / Q000187:drug effects
D006993:Hypnotics and Sedatives; D002110:Caffeine; D019284:Thapsigargin; D013874:Thiopental; D002118:Calcium