Cyclic AMP,Transmitter Release and the Effect of Adenosine on Neuromuscular Transmission

THE high activities of the enzymes in nervous tissue regulating the metabolism of 3',5' adenosine monophosphate (cyclic AMP) and its apparent involvement in secretion from glands have prompted considerable speculation about its possible role in the release of transmitters from nerve endings^1–4. There is some evidence that cyclic AMP is concerned in the release of acetylcholine from motor nerve endings^1,3. It has been found, for example, that neuromuscular transmission is facilitated by catecholamines^5,6 and methylxanthines^1,3; noradrenaline is known to increase both the quantal content of the endplate potential⁶ and the level of cyclic AMP in nervous tissue^7,8 and the increase in the quantal content is more marked in the presence of theophylline³. It was also found that increases in cyclic AMP concentration of up to thirty-fold occur in brain slices in the presence of 0.1-1 mM adenosine. We have therefore examined the effect of this substance on transmitter release.