Dexmedetomidine-induced contraction of isolated rat aorta is dependent on extracellular calcium concentration

BACKGROUND: Dexmedetomidine is a highly selective α(2)-adrenoceptor agonist that is widely used for sedation and analgesia during the perioperative period. Intravenous administration of dexmedetomidine induces transient hypertension due to vasoconstriction via the activation of the α(2)-adrenoceptor on vascular smooth muscle. The goal of this in vitro study is to investigate the calcium-dependent mechanism underlying dexmedetomidine-induced contraction of isolated endothelium-denuded rat aorta. METHODS: Isolated endothelium-denuded rat thoracic aortic rings were suspended for isometric tension recording. Cumulative dexmedetomidine concentration-response curves were generated in the presence or absence of the following inhibitors: α(2)-adrenoceptor inhibitor rauwolscine; voltage-operated calcium channel blocker verapamil (5 × 10(-7), 10(-6) and 5 × 10(-5) M); purported inositol 1,4,5-trisphosphate receptor blocker 2-aminoethoxydiphenylborate (5 × 10(-6), 10(-5) and 5 × 10(-5) M); phospholipase C inhibitor U-73122 (10(-6) and 3 × 10(-6) M); and store-operated calcium channel inhibitor gadolinium chloride hexahydrate (Gd(3+); 5 × 10(-6) M). Dexmedetomidine concentration-response curves were also generated in low calcium concentrations (1 mM) and calcium-free Krebs solution. RESULTS: Rauwolscine, verapamil, and 2-aminoethoxydiphenylborate attenuated dexmedetomidine-induced contraction in a concentration-dependent manner. Low calcium concentrations attenuated dexmedetomidine-induced contraction, and calcium-free Krebs solution nearly abolished dexmedetomidine-induced contraction. However, U-73122 and Gd(3+) had no effect on dexmedetomidine-induced contraction. CONCLUSIONS: Taken together, these results suggest that dexmedetomidine-induced contraction is primarily dependent on extracellular calcium concentrations that contribute to calcium influx via voltage-operated calcium channels of isolated rat aortic smooth muscle. Dexmedetomidine-induced contraction is mediated by α(2)-adrenoceptor stimulation. Dexmedetomidine-induced contraction appears to be partially mediated by calcium release from the sarcoplasmic reticulum.