The influence of adenylate cyclase inhibitors on the spontaneous activity of the cardiac pacemaker.

The effects of adenylate cyclase inhibitors, haloperidol and chlorpromazine, on the spontaneous activity of the rabbit sinus node was studied by means of double sucrose gap and intracellular microelectrodes. Haloperidol and chlorpromazine arrested the spontaneous activity which could be restored with noradrenaline, in the presence of haloperidol, or with dibutyryl c AMP, in the presence of either inhibitor used. After arresting of the spontaneous activity, sinus node cells might utilize metabolic energy supplied from exogenous pyruvate. Pyruvate protected from depolarization or reestablished polarization in depolarized cells but was not able to restore the spontaneous activity. Discussion of these results suggests that c AMP may be directly involved in the spontaneous electrogenesis in the sinus node.