Effect of pentobarbital, verapamil and manganese on the frequency-force relationship of the isolated atrium and ventricle of the dog heart.

The canine right atrium was perfused with arterial blood led from a carotid artery of the heparinized support dog and suspended in a bath filled with blood. In 5 non-spontaneously beating preparations, the frequency-force relationship was investigated by electric stimulation at a frequency range from 0.017 to 3 Hz. At a low frequency level, a large peak tension developed. At 0.5 Hz, minimum values of developed tension were obtained. At a range of 0.5-3 Hz, the developed tension increased with the frequency. Higher frequencies than 4 Hz usually caused pulsus alternans. The staircase phenomena were not influenced by treatment with propranolol or atropine. Therefore, there may be no participation of the autonomic nerve stimulation on the frequency-force relationship. Effects of pentobarbital, (+/-)-verapamil and manganese on the frequency-force relationship were investigated with both the blood-perfused, isolated atrium preparations and isolated ventricular preparations. Pentobarbital and manganese chloride produced a uniform depression of the developed tension at all frequencies but the depression with (+/-)-verapamil was greater at higher frequencies in both atrial and ventricular muscles.