Swelling and Shrinkage Phenomena in Liver Mitochondria

Abstract

Addition of Mg^++ chelating agents such as EDTA or citrate, to liver mitochondria results in an increased permeability of the mitochondrial membrane to univalent cations. EDTA supplemented mitochondria show reversible swelling shrinkage cycles which are coupled to movement of univalent cations in and out the mitochondrion. The uptake of univalent cations requires either respiration or ATP and is therefore accompanied by stimulation of respiration or by ATPase activity. The release of cations is driven by a concentration gradient. The inhibitory effect of dinitrophenol on the swelling process has also been studied. Mg^++ inhibits the swelling due to EDTA or causes shrinkage if added after the swelling has occurred. Inhibition of respiration accompanies the shrinkage due to Mg^++. It is suggested that the “tightly coupled state” of mitochondria is partly due to a low permeability of the mitochondrial membrane to univalent cations and that this permeability is physiologically controlled by the membrane bound Mg^++.