AN ANALYSIS OF THE ACTION OF ACETYLCHOLINE ON HEARTS, PARTICULARLY IN ARTHROPODS

Abstract

The effects of drugs upon the hearts of a number of arthropods have been investigated by immersion of the specimens in test solutions. Acetylcholine, potassium and other substances affect the heart of a crayfish when they enter through the body surface (gills) although the threshold is much higher than when the drugs are applied directly to the heart. Two amphipods, the marine Talorchestia longicornis and the blind freshwater Bactrurus mucronatus show cardiac acceleration by acetylcholine. The heart of the blind freshwater isopod Asellus tridentatus is accelerated by acetylcholine as are the hearts of the copepods Diaptomus oregonensis and Diaptomus sanguinensis. The heart of Artemia salina is unaffected by acetylcholine even in very high concentrations, with or without eserine. Eserine alone has a toxic depressing action on Artemia. The Eubranchipus heart is also unaffected by acetylcholine. Dye penetration and injection experiments show that the lack of acetylcholine action on Artemia is not due to lack of penetration. Pure adrenalin is without effect on the Artemia hearts, but adrenalin solution (Parke, Davis) markedly inhibits due to the reducing agent sodium bisulfite. Limulus embryos during the myogenic period of heart contraction (21 to 33 days of development) show no effect of acetylcholine. Acceleration appears along with innervation. A comparison of the effects of acetylcholine with the presence of extrinsic innervation and of ganglionic pacemakers shows the following: The hearts of higher arthropods and of some annelids and tunicates which are accelerated are neurogenic. The hearts of adult vertebrates, of molluscs and probably Daphnia which are inhibited by acetylcholine are myogenic but innervated. Embryonic hearts of vertebrates, Limulus, and the hearts of Artemia and Eubranchipus are unaffected by acetylcholine and are probably non-innervated.