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

1. Radio-isotopes have been used to study the effect of noradrenaline on the permeability of the taenia of the guinea-pig caecum to inorganic ions. The preparations were bathed at either 10 or 20 degrees C in solutions containing a high concentration of potassium, in order to depolarize the fibres and so avoid ionic movements secondary to changes in membrane potential.2. Under these conditions noradrenaline increased both inward and outward fluxes of potassium whilst having little effect on the exchange of chloride.3. No effect of noradrenaline on the uptake of sodium 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 potassium exchange.4. These results are discussed in relation to the hypothesis that an increase in potassium permeability contributes to the inhibitory actions of noradrenaline on intestinal smooth muscle.