Effects of cholinergic agents on the metabolism of choline in muscle from Ascaris suum

Abstract

The incorporation of [methyl-14C]choline into the choline-containing compounds of Ascaris suum muscle and the effects of acetylcholine and its agonists, carbachol and levamisole, on this incorporation were studied. Previous experiments reported a stimulation of phosphatidylcholine (lecithin) metabolism upon the administration of acetylcholine. Acetylcholine administered in vitro to A. suum muscle and body wall preparations resulted in a stimulation of phospholipase C activity that, in turn, produced an increased rate of hydrolysis of phosphatidylcholine to the corresponding diacylglyceride (DAG). The DAG, in turn, may act as a second messenger as it is required for the activation of an A. suum protein kinase C. Evidence presented here is in accordance with this hypothesis. The administration of cholinergics resulted in a stimulation of phosphatidylcholine turnover. Acetylcholine also stimulated isotope incorporation into glycerophosphorylcholine, presumably as a consequence of enhanced phospholipid turnover. These events appear to be associated with the ligand binding to the acetylcholine receptors of the A. suum muscle. Choline kinase activity is suggested in order to maintain the observed high ratio of phosphorylcholine to choline. Findings indicate that in the parasite's muscle phosphatidylcholine metabolism may be linked to receptor-dependent responses and subsequent signal transduction.