Abolition by nicorandil of spontaneous action potentials of the small atrio-ventricular node preparation of the dog.

: Effects of carbachol and nicorandil on spontaneous action potentials were examined in the small atrio-ventricular (A-V) node preparation of the dog. Carbachol (3 X 10(-6) M) definitely hyperpolarized the membrane potential and abolished the spontaneous activity. Nicorandil (3 X 10(-4) M) also abolished the spontaneous activity but the membrane potential became quiescent at -65 mV, which was less negative than the maximum diastolic potential. From these results it appears that nicorandil may increase the potassium conductances but not hyperpolarize the membrane potential because the background potassium conductance is little developed in the nodal cells.