EFFECTS OF INTRACELLULARLY APPLIED CYCLIC 3', 5'-ADENOSINE MONOPHOSPHATE AND DIBUTYRYL CYCLIC 3', 5'-ADENOSINE MONOPHOSPHATE ON THE ELECTRICAL ACTIVITY OF SINOATRIAL NODAL CELLS OF THE RABBIT

¹ Department of Pharmacology, Faculty of Medicine, Kyoto University, Sakyo-ku, Kyoto 606, Japan

Cyclic 3', 5'-adenosine monophosphate (cyclic AMP) and dibutryryl cyclic 3', 5'-AMP were iontophoretically injected into sinoatrial nodal cells of isolated rabbit atria. Intracellularly applied dibutyryl cyclic AMP caused an increase in the slope of diastolic depolarization which was accompanied by an acceleration of the atrial rate. Similar changes in the slope of diastolic depolarization and atrial rate was observed after an intracellular application of cyclic AMP when preparations were exposed to 10^-4 M theophylline. These effects of both drugs were not inhibited by 10^-6 M propranolol added to the bathing medium. Intracellularly applied 5'-AMP did not produce changes in pacemaker activities. Atrial rate was not accelerated by 2 x 10^-3 M cyclic AMP added to the bathing medium even when the preparations were pretreated with 10^-4 M theophylline but was accelerated by dibutyryl cyclic AMP. It may be concluded that intracellular cyclic AMP can cause an acceleration of the atrial rate associated with changes in the permeability of membrane of pacemaker cells for ions.

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