Reduction of potassium permeability by chloride substitution in cardiac cells.

Abstract

The efflux of radioactive K+ and Cl- was measured in cow Purkinje fibers and ventricular preparations of cow, cat and frog. The effect of K+ and Cl- was studied by changing the extracellular K+ concentration [K+] between 0-54 mM, and by substituting Cl- by acetylglycinate, isethionate, benzenesulfonate, propionate and nitrate. In the absence of Cl the rate coefficient for 42K efflux showed a pronounced fall, which was more pronounced the higher the [K+]. This effect was not related to the change in membrane potential. The rate coefficient for 42K efflux increased in the presence of higher extracellular [K+]. 36Cl efflux increased in the presence of reduced as well as increased extracellular [K+]. The calculated permeability coefficient for K (PK) was maximal at 5.4 mM-K, decreased slightly at higher [K+] but fell markedly in K-free solutions, (to about 1/5 of the value in 5.4 mM-K). In Cl-free medium PK reduced to 0.67 of the value in the Cl medium, irrespective of the [K+]. The calculated PCl was greater in K-free and 16.2 mM-K than in 5.4 mM-K. The ratio PK/PCl showed important changes as a function of extracellular [K+]: the value was 5 in 5.4 mM-K and fell to 2 and 0.5, respectively, in 16.2 and K-free solutions. Part of the changes in membrane resistance measured by electrical methods in Cl-free media is apparently due to a simultaneous decrease in K conductance.