Indexed on: 25 Aug '11Published on: 25 Aug '11Published in: Canadian journal of physiology and pharmacology
Dexmedetomidine, a full agonist of the α2B-adrenoceptor that is mainly involved in vascular smooth muscle contraction, is primarily used for analgesia and sedation in intensive care units. High-dose dexmedetomidine produces hypertension in children and adults. The goal of this in vitro study was to investigate the role of the calcium (Ca(2+)) sensitization mechanism involving Rho-kinase, protein kinase C (PKC), and phosphoinositide 3-kinase (PI3-K) in mediating contraction of isolated rat aortic smooth muscle in response to dexmedetomidine. The effect of dexmedetomidine on the intracellular Ca(2+) level ([Ca(2+)]i) and tension was measured simultaneously. Dexmedetomidine concentration-response curves were generated in the presence or absence of the following antagonists: rauwolscine, Y 27632, LY 294002, GF 109203X, and verapamil. Dexmedetomidine-induced phosphorylation of PKC and membrane translocation of Rho-kinase were detected with Western blotting. Rauwolscine, Y 27632, GF 109203X, LY 294002, and verapamil attenuated dexmedetomidine-induced contraction. The slope of the [Ca(2+)]i-tension curve for dexmedetomidine was higher than that for KCl. Dexmedetomidine induced phosphorylation of PKC and membrane translocation of Rho-kinase. These results suggest that dexmedetomidine-induced contraction involves a Ca(2+) sensitization mechanism mediated by Rho-kinase, PKC, and PI3-K that is secondary to α2-adrenoceptor stimulation in rat aortic smooth muscle.