Some effects of noradrenaline on electrical activity of guinea-pig ureteric smooth muscle

THE double sucrose-gap was used to investigate the electrophysiological basis for the positive inotropic effect of noradrenaline on the isolated guinea-pig ureter. In unmodified Krebs solution noradrenaline (1×10−5 g/ml) increased the duration of the action potentnal and increased the number, but decreased the amplitude, of the superimposed spikes. This change in action potential configuration was paralleled by an increase in the force and duration of the mechanical response. Ion substitution experiments suggest that the most important action of noradrenaline is the enhancement of the slow inward current carried by sodium ions. No evidence was found for a chloride or potassium contribution to the noradrenaline effect.