“Action Currents” Without Rhythmic Contractions and Rhythmic Contractions Without “Action Currents.”

Abstract

The present-day teaching is that action currents obtained from contracting muscle are due to physico-chemical changes associated with the shortening of the fibres. Against this view is the fact that electrocardiograms have been obtained during experiments in which the heart-beat was, to all appearances stopped, by the removal of calcium from the nutrient fluid or by other means. Similarly, we have been able to show that the characteristic electrogram that is associated with the rhythmic contractions of the bowel persists long-after the muscular movements have been stopped by epinephrine.

Rabbits were used, anesthetized with urethane, and with the abdomen open in a bath of physiologic saline solution. The loops of bowel being studied were kept in a layer of mineral oil, which floated on the surface of the salt solution. The electrodes consisted of steel wire serrefines plated with silver and silver chloride, and so suspended on pivots that the movements of the bowel could be recorded simultaneously with the electrogram. A string galvanometer was used. Details of the technic will be published in a paper now in press.

In a typical experiment with epinephrine, 0.15 cc. of a 1 to 1000 solution was injected into the ear vein. Within 10 seconds the contractions of the bowel disappeared while the electrical changes persisted. The only modification in the electrical record consisted of a greater regularity of the waves and a more rapid rate. In one experiment the increase was from 9 to 12 cycles a minute. After 105 seconds the mechanical contractions returned in the lower part of the bowel and the electrical variations were then found to be in phase with them.

In an attempt to explain this phenomenon we were at first inclined to assume that something had happened to one of the links in the chain of chemical processes that bring about contraction in the muscle fibers; to use a metaphor derived from the field of mechanics, the engine continued to run after a clutch of some kind was thrown out.