Cholinesterases and choline acetyltransferase in the ductus deferens of the guinea-pig.

Several authors have reported that longitudinal and circular muscle layers of the guinea-pig ductus deferens possess a rich adrenergic innervation. Cholinergic innervation has been doubted by several authors, especially its presence in the longitudinal muscle layer. Acetylcholinesterase and butyrylcholinesterase were demonstrated, by electron-microscopic examination of both muscle layers of the guinea-pig ductus deferens, to be localized on the axolemma of the nerve endings and in smooth-muscle fibres, on sarcolemma, in the intracellular caveolae and in the intercellular space. Activity of cholinesterases and choline acetyltransferase was measured by the radiometric method and was found in both muscle layers. The activity of butyrylcholinesterase was higher than that of acetylcholinesterases in the homogenates of the whole ductus deferens and in the longitudinal muscle layer. In the circular muscle layer, the activity of acetylcholinesterase was higher than the activity of butyrylcholinesterase. In both muscle layers, we also found choline acetyltransferase, the activity being stronger in the circular layer. The localization of cholinesterases in smooth-muscles in the same places as the calcium and muscarinic acetylcholine receptors is discussed, together with the possibility that the enzyme is in some way involved in the excitation-contraction mechanism of smooth muscle.