Effects of Reduction of External Sodium Chloride on the Injury Potentials of Cardiac Muscle

Abstract

During cardiac activity an injured area becomes electrically positive toward quiescent uninjured cardiac muscle. The action potentials of nerve axon, striate muscle and cardiac muscle markedly exceed the resting potential as a result of an increased permeability to Na+ during activity. Reduction of external Na+ reduces the excess of action over resting potential. In testing the effect of Na+-deficient perfusates on the positive phase of the cardiac injury potential, injury potentials were produced with the Wiggers suction electrode. The heart of Chelydra serpentina was exposed and perfused in situ with normal Ringers and Ringers in which the NaCl was reduced to 1/3 of normal, made isosmotic with glucose. The area of the normal negative phase in millivolt-seconds was 31 [plus or minus] 2.5,the area of the negative phase with Na[long dash]deficient perfusates was not significantly different. The area of the normal positive phase was 10.4 [plus or minus] 1.4, the area of the positive phase with Na-deficient perfusates was 5.8 [plus or minus]1.3, significantly different. This decrease in area, the result of a decrease in both amplitude and duration of the positive phase, suggests the mechanisn,by which injured cardiac muscle becomes electrically positive to resting uninjured muscle,is similar to the pehnomena explained by Hodgkin on the basis of Na+ permeability.