EFFECT OF VASODILATORS UPON THE ISOLATED TAENIA CULI OF THE GUINEA PIG

¹ Department of Pharmacology, Faculty of Medicine, Tokyo Medical and Dental University, Yushima, Bunkyo-ku, Tokyo, Japan

Using the isolated guinea-pig taenia coli, the smooth muscle relaxing actions of nitroglycerin (NG), adenosine (Ads), papaverine (Pap) and aminophylline (AMPH) were examined, in comparison with that of epinephrine (Epi). The electrical activity was recorded with the sucrose-gap method. Associated with their relaxant actions, an inhibition of spontaneous spike discharge and a hyperpolarization were observed. In the depolarized muscle, the effects of NG, Ads and Epi were abolished, whereas those of Pap and AMPH persisted. After Pap, the maintained phase of K-contracture disappeared, while AMPH abolished the initial phasic response. In media with 10^-8 M calcium, in which the relaxant effect of AMPH on depolarized muscle was eliminated, Pap was still effective. The smooth muscle relaxing action of NG, Ads and Epi was ascribed to their inhibitory action on the electrical activity. Pap was considered to act on the "bound" calcium, besides its action on the membrane potential. Inhibition of the calcium permeability was postulated for the action of AMPH.