Cytochemical localization of cyclic 3', 5'-nucleotide phosphodiesterase activity in the neuromuscular junction and skeletal muscle of the newt.

The localization of cyclic 3', 5'-nucleotide phosphodiesterase activity at the neuromuscular junction and in skeletal muscle of the newt was studied cytochemically. In the axon terminal, activity was localized to a site on the membranes of synaptic vesicles. In skeletal muscle, activity occurred in the sarcoplasmic reticulum but was restricted to the longitudinal tubules. Junctional folds of the motor end plate were unreactive. These findings are suggestive of a role of cyclic AMP in the functions of synaptic vesicles and sarcoplasmic reticulum and indicate its effects are terminated at these sites.