The effect of noradrenaline on the permeability of depolarized intestinal smooth muscle to inorganic ions

Abstract

Radio-isotopes were used to study the effect of noradrenaline [norepinephrine] on the permeability of the taenia of the guinea-pig caecum to inorganic ions. The preparations were bathed at either 10 or 20[degree]C in solutions containing a high concentration of K, in order to depolarize the fibers and so avoid ionic movements secondary to changes in membrane potential. Under these conditions noradrenaline increased both inward and outward fluxes of potassium while having little effect on the exchange of chloride. No effect of noradrenaline on the uptake of Na could be detected, whereas carbachol (carbamyl choline chloride), applied under identical conditions, caused a significant increase at a concentration chosen to match the effect of noradrenaline on K exchange. These results are discussed in relation to the hypothesis that an increase in K permeability contributes to the inhibitory actions of noradrenaline on intestinal smooth muscle.