Our study examined whether calcium channels are involved in the anesthetic action of dexmedetomidine (100-300 micrograms/kg), a highly selective alpha 2-adrenoceptor agonist. To investigate this, we studied the effects of verapamil (1.25 or 2.5 mg/kg), a calcium channel blocker, and BAY K8644 (0.5 or 1 mg/kg), a calcium channel agonist, on the hypnotic-anesthetic effect of dexmedetomidine in rats. Loss of the righting reflex was used to determine the presence of anesthesia, and its length in minutes was referred to as the duration of hypnosis. Verapamil significantly enhanced the duration of the hypnotic-anesthetic action of dexmedetomidine (P less than 0.05). In contrast, BAY K8644 caused a significantly increased onset of hypnosis (P less than 0.001) and attenuated the anesthetic property of dexmedetomidine. These results suggest that the hypnotic-anesthetic action of dexmedetomidine is influenced by the activation/gating of calcium channels.