Rapid, Respiration-independent Binding of Alkali Metal Cations by Rat Liver Mitochondria

Abstract

Abstract When rat liver mitochondria suspended in salt-free 0.25 m sucrose solution are mixed with weakly buffered solutions of NaCl, the suspending medium undergoes very rapid acidification. This reaction was found to proceed in the absence of electron transport. The amount of acid produced increased with increasing NaCl concentration, with increasing initial pH, and with increasing concentration of mitochondria. The H+ released exceeded 35 nmoles per mg of protein. Similar effects were given when NaCl was replaced by chlorides of other univalent cations; the relative activities were Li+ g NH4+ g choline+ g Na+ g K+ g Rb+ g Tris+. The acidification requires the presence of a salt; as little as 2.5 mm NaCl produced measurable H+ release. Acid-base titration curves of intact rat liver mitochondria were increasingly displaced to the acid side by increasing NaCl concentration. Flame photometry of mitochondria isolated after mixing with NaCl (or LiCl) solutions showed that Na+ (or Li+) was bound to the mitochondria in an amount that was equimolar to H+ released. This interaction was not intrinsically affected by 2,4-dinitrophenol, gramicidin, or valinomycin. During binding of Na+ and equimolar release of H+, endogenous K+ and Mg++ were lost from the mitochondria to the medium in the absence of valinomycin or other permeability-inducing agents. These observations on binding of alkali metal cations appear to provide a possible basis for their action in increasing the Ca++:O accumulation ratio during energy-linked Ca++ uptake to superstoichiometric levels.