NORADRENERGIC NEURONS RELEASE BOTH NORADRENALINE AND NEUROPEPTIDE-Y FROM A SINGLE POOL - THE LARGE DENSE CORED VESICLES

In peripheral adrenergic nerve endings, noradrenaline is stored in two different types of vesicles, the large and the small dense cored vesi cles. A systematic study was undertaken to examine the release of nora drenaline and neuropeptide Y from dog spleen and rat vas deferens unde r various conditions of stimulation, particularly those which previous ly have demonstrated a differential regulation of exocytosis of the di fferent types of storage vesicles. Here we present evidence that norad renaline is released by exocytosis exclusively from the large dense co red vesicles, in which it is stored together with neuropeptide Y. Upon a single stimulation (at frequencies varying from 2-20 Hz), the relea se of noradrenaline and neuropeptide Y from the dog splenic nerve incr eased with the frequency of stimulation, but the ratio of noradrenalin e to neuropeptide Y remained constant, After repeated stimulation of t he splenic nerve, both substances' overflow decreased gradually and in parallel to values of 12.5% and 11.1% of the first stimulation for no radrenaline and neuropeptide Y, respectively, Similarly, repeated stim ulation of the rat vas deferens (of which only 2-10% is large dense co red vesicles, whereas in the dog splenic nerve the large dense cored v esicles make up 30-40% of the total vesicle population) with 120 mM K, in the presence of phentolamine, caused a gradual and parallel decli ne in the release of noradrenaline and neuropeptide Y (31.6% and 34.0% , respectively). Moreover, omega-conotoxin (10(-8) M to 10(-5) M) had a similar inhibitory effect on the release of both substances. alpha-l atrotoxin (10(-9) M) evoked a parallel release of both noradrenaline a nd neuropeptide Y. The results indicate that noradrenaline in peripher al noradrenergic nerves is released exclusively from large dense cored vesicles by an exocytotic mechanism. (C) 1997 Wiley-Liss, Inc.