Abstract
The papillary muscle of the canine right ventricle was perfused at a constant pressure of 100mm Hg with the blood from a donor dog by a cross-circulation technique. The papillary muscle was isometrically contracted by electrical stimulation through bipolar platinum electrodes, at 0.5 to 1.5 volts (the voltage approximately twice the threshold), 5 msec and 120 per min. When the strength of electrical stimulation was raised either with high voltage or with long pulse-duration at a constant frequency of 120 per min, the positive inotropic response was obtained in parallel with increasing strength of the stimulation. The positive inotropic response by increasing voltage was apparently enhanced by atropine and hemicholinium, and blocked by β-adrenergic blocking agent and tetrodotoxin. Guanethidine treatment converted the positive inotropic response to the pronounced negative one, which was blocked by atropine. These facts present some evidence that not only adrenergic but also cholineruie nerve. fibers exist, in the canine papillary muscle.
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