Recycling of noradrenergic storage vesicles of isolated rat vas deferens

Abstract

Del Castillo and Katz established the theory of quantal release of acetylcholine from the neuromuscular junction¹. The concept was expanded by showing that quanta of transmitter was packaged in, and released from, storage vesicles of the nerve endings. Noradrenaline (NA) is also believed to be stored in, and released from, storage vesicles of the sympathetic nerves. The requirement of Ca for NA release² and concomitant secretion of the vesicular enzyme, dopamine-β-hydroxylase³, on stimulation lends strong evidence to the theory of exocytosis. However, it remains unclear whether storage vesicles after fusing with neuronal membrane to release NA into cleft, are once again reused for further storage and release of NA, or are discarded by the nerve endings. I have investigated this question by making use of the fact that tetraethylammonium (TEA) causes profound facilitation of the overflow of ³H-NA when the sympathetic nerves of the isolated vas def erens are electrically excited⁴, and that this excess release is accompanied by a significant reduction in tissue NA content⁵. The principal advantage of the method is that the reduction in tissue NA content is effected exclusively by the exocytotic release of NA from the nerve terminals and easy washout of TEA allows one to study uptake of exogenous NA by the tissue. The results presented here support the hypothesis that NA storage vesicles are recycled.