Activation of potassium ion transport in mitochondria by cadmium ion

Abstract

Low levels of Cd2+ (1-5 .mu.M) produce rapid swelling of [rat liver] mitochondria, which is respiration-dependent and uncoupler-sensitive. No cation requirement is apparent, since the swelling occurs in a medium containing only sucrose and the respiratory substrate. The swelling is inhibited by ruthenium red, suggestiing that this effect of Cd2+ requires its entry into mitochondria. In medium containing 9 mM K+, addition of Cd2+ along with ruthenium red increases the rate of K+ influx 3-fold. In the presence of K+, Rb+ or Li+, but not of Na+, addition of Cd2+ produces first efflux of H+ into the medium followed by discharge of the pH gradient or uncoupling. Only the latter effect is inhibited by ruthenium red, showing that the efflux and influx of H+ are independent reactions. The H+ efflux appears to be an antiport response to the induced K+ entry. Its activation by Cd2+ is similar to the known effect of p-chloromercuriphenyl sulfonate. The H+ influx or uncoupling appears to result from binding of Cd2+ to some matrix-facing membrane site, perhaps the dithiol group on coupling factor B, and may relate to apparent permeability changes associated with Cd2+-induced swelling.