[Possible participation of slow Na+--Ca++ channels in realizing cholinergic effects on the cardiac pacemaker].

The effect of the Ca++-permeability inhibitors (Mn ions, Verapamil, D-600) on the bioelectrical activity and cholinergic responses of isolated sinus node involved reduction of the pacemaker rhythm within 30-40 min and a complete inhibition of the bioelectrical discharge as well as a diminished amplitude of the AP and a reduced slope of the slow diastolic and the fast depolarization. The findings seem to be due to an inhibiting of the slow Na+-Ca++ influx by Ca++-antagonists. The prolonged APs and the reduced rate of terminal repolarization might be due to effect of the inhibition on potassium permeability.

[Relation between intracardiac reflex effects on the rate of atrioventricular conduction and parameters of neural pathway stimulation].

Intracardiac nerves of the frog isolated heart were cut and the central or the peripheral end was stimulated. The atrioventricular (a-v) conduction was measured. The data showed that the intracardiac parasympathetic nervous system could induce both acceleration and deceleration of the a-v conduction, depending on the parameters of stimulation.

[Mechanical action of the atria during stimulation on the work of the sinus node].

The cardiac pacemaker and atria were removed from the frog heart and placed into a chamber with Ringer solution. Atrial pacing was performed at a suprathreshold milliamperage. The mechanism of changes in the cardiac pacemaker during atrial pacing was studied both under the conditions of the blockade of the intracardiac nervous system and elimination of the bioelectrical and mechanical effects of the atria on the cardiac pacemaker.

[Role of the atrium in the functional organization of the sinoatrial node].

The automatic activity of the venous sinus was studied in respect to the atrial bioelectrical activity in frogs. Each of the two parts of the divided venous sinus had different rhythms. Extra-cellular recording revealed that the APs of both parts of the sinus were closely synchronized if the parts were connected with the atrium.