Abstract
A method of preparing and employing the isolated heart of the quahog, Venus mercenaria, for the bioassay of acetylcholine is described. This prepn. has certain advantages over the classical acetylcholine assay prepns. The activities of choline and certain choline esters, of betaine and betaine ethyl ester, and of triethylcholine and triethylacetylcholine on the isolated Venus heart were compared. Acetylcholine was the most active of the several choline esters which were tried. In further understanding the mode of action of acetylcholine, the most significant observation was that the substitution of ethyl groups for methyl attached to the N of choline and acetylcholine resulted in a complete loss of ability to depress the amplitude of heart beat.