THE MECHANISM OF ACTION OF ACETYLCHOLINE ON THE VENUS HEART

¹ The Biological Laboratories, Harvard University, Cambridge, Massachusetts

1. The relationship between electrical stimulation and inhibition by acetylcholine has been studied in the Venus heart.

2. Stimulation of the heart with direct current produced negative inotropic, chronotropic, and tonotropic effects when anodal, and produced positive chronotropic and tonotropic effects when cathodal. The reversibility of the response with changing polarity is taken as an indication that the step in the regulatory process influenced by electrical stimulation is itself fundamentally electrical.

3. A chemical response to electrical stimulation was demonstrated by the effect on a receptor heart of fluid perfused from a stimulated donor heart.

4. An electrical response to acetylcholine is shown by changes in the ECG. These changes are interpreted as changes in conduction velocity of two propagated monophasic components of opposite sign.

5. The acetylcholine-blocking agent tetraethylammonium bromide is shown to antagonize anodal effects and to augment cathodal effects in this tissue.

6. These interactions between electrical and chemical aspects of the beating of the Venus heart suggest that the acetylcholine system is intimately associated with the electrical aspects of excitation.