Smooth muscle contraction in presence of an inhibitor of K efflux

Contractions of the isolated longitudinal smooth muscle from guinea pig ileum produced by pilocarpine are regularly accompanied by increases in the efflux of potassium ion. A concentration of 7.4 x 10 –6 m pilocarpine produced a maximum smooth muscle contraction and an increase in potassium efflux which averaged 157% above that of unexcited fibers. In the presence of appropriate concentrations of the inhibitor (desoxycorticosterone acetate) pilocarpine evoked small to negligible increases in potassium efflux, whereas the smooth muscle contractions elicited were about 81% of the control. These data show that pilocarpine can produce a near maximal smooth muscle contraction in the absence of any pronounced change in outward flux of potassium ion.