Effect of the external concentrations of potassium and sodium on the release of (−)-[3H]noradrenaline from the adrenergic nerves of the rat vas deferens

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Abstract
The effect of the external concentrations of sodium and potassium on the nerve-induced release of (−)-[3H]noradrenaline from the adrenergic nerves of the rat vas deferens has been investigated. Increasing the external potassium concentration above 5 mM decreased the amount of noradrenaline released, while reducing the external potassium concentration below 5 mM had no significant effect on the induced release of noradrenaline. Decreasing the external sodium concentration below 75 mM progressively decreased the release of noradrenaline. It is concluded that the amplitude of the action potential is optimum for release at the normal resting membrane potential, and only decreasing the amplitude of the action potential alters the amount of transmitter released per nerve impulse.