Enrichment of cyclic adenosine 3',5'-monophosphate and cyclic guanosine 3',5'-monophosphate in cholinergic axon terminals of the Torpedo electric organ.

On fractionation of intact electric organ, cAMP and cGMP are enriched in the synaptosome fraction by factors of 14 and 6 respectively. For all regions of the electromotor neuron the absolute contents of nucleotides are in the order ATP greater than cAMP greater than cGMP. However, the molar ratios of cAMP/cGMP vary between tissues. Specific contents of both cyclic nucleotides are lowest in the nerve. For cAMP, specific contents in the axon terminal and in the perikaryal region are similar. As compared to this, cGMP is considerably enriched in the presynaptic nerve ending. This points to a physiological role of cGMP in presynaptic function.