Large conductance Ca²⁺-activated K⁺ channels inhibit vagal acetylcholine release at the rabbit sinoatrial node

Although large conductance Ca²⁺-activated K⁺ (BK) channels play an important role in determining vascular tone, their role in the efferent cardiac vagal system remains to be elucidated. In anesthetized rabbits (n=9), acetylcholine (ACh) was measured at the right atrium near the sinoatrial node by a cardiac microdialysis technique, and the ACh release in response to electrical stimulation of the cervical preganglionic vagal nerves was examined. Local administration of a BK channel blocker iberiotoxin (2μM) through a dialysis fiber increased the stimulation-induced ACh release from 7.6±2.7 to 9.0±3.2nM (P<0.05). Addition of intravenous administration of iberiotoxin (0.11mg/body) did not increase the stimulation-induced ACh release further (10.8±4.4nM). These results indicate that the BK channels play an inhibitory role in the vagal ACh release to the sinoatrial node.