Swelling and contraction of the mitochondrial matrix. II. Quantitative application of the light scattering technique to solute transport across the inner membrane

Abstract

The relationship between matrix volume and the amount of light scattered by a mitochondrial suspension has been characterized for equilibrium measurements and shown to depend in a complex but predictable manner on native structure of the mitochondrion (Beavis, A. D., Brannan, R. D., and Garlid, K. D. (1985) J. Biol. Chem. 260, 13424-13433). In the present report, we show that this characterization also applies to kinetic measurements of salt and nonelectrolyte transport. We derive and evaluate quantitative methods for determining permeability constants from light scattering kinetics. We apply these equations to the problem of whether matrix swelling itself induces permeability changes secondary to membrane stretching or changes in surface available for transport. A study of erythritol transport over a 7-fold range of matrix volume reveals dramatic changes in light scattering rates, as previously observed (Tedeschi, H. (1959) J. Biophys. Biochem. Cytol. 6, 241-252). These transitions correspond exactly to structure-dependent transitions in the relationship between absorbance and matrix volume. When this is taken into account, erythritol permeability is found to be constant over the entire volume range. Factors affecting intrinsic membrane porters, such as Mg2+ depletion and dicyclohexylcarbodiimide, are also found to be without effect on erythritol permeability. The broader significance of this study is that the light scattering technique is shown to be capable of providing quantitative answers to important questions about solute transport across the inner membrane.