EFFECTS OF ANGIOTENSIN, BRADYKININ AND OXYTOCIN ON ELECTRICAL AND MECHANICAL ACTIVITIES IN THE TAENIA COLI OF THE GUINEA PIG

There have been published a number of papers dealing with the action of pharmacologically active polypeptides such as angiotensin, bradykinin and oxytocin on the visceral smooth muscle (1-9). However, no one has investigated into their effects on the membrane potential. Since the work of Evans and Schild (10, 11) it has been generally accepted that the effect on the spike generating mechanisms of smooth muscle is not only one way through which drugs can exert their actions on the contractility of smooth muscle. In other words, drugs would influence the contraction of smooth muscle without direct relationship to the spike discharges. Therefore it is highly desirable to observe the effect of these polypeptides on the membrane potential of smooth muscle simultaneously with their effect on the mechanical activity. The present studies were carried out along this line with the taenia coli of the guinea pig by recording changes in the membrane potential and spike discharges concurrently with the tension change. In the present article, it is also intended to decide the site of action of these polypeptides as it is uncertain whether they would act on smooth muscle directly or indirectly through nervous elements in smooth muscle. In contrast with some of the previous reports (1, 3, 4), which insisted on the participation of the indirect mechanism, it was revealed that all the three polypeptides act directly on the smooth muscle cells. Some of the results have been reported in brief (12).