Ion permeability induced in artificial membranes by the ATP/ADP antiporter

Abstract

The hypothesis on the additional function of the ATP/ADP antiporter (ANT) as uncoupling protein has been tested in proteoliposomes and planar bilayer phospholipid membranes (BLM). It is found that dissipation of the light-induced ΔpH in the dark is very much faster in ANT-bacteriorhodopsin proteoliposomes than in proteoliposomes containing baeteriorhodopsin as the only protein. Mersalyl treatment of ANT-bacteriorhodopsin proteoliposomes causes further increase in the ΔpH dissipation rate due to formation of a high conductance pore. The properties of this pore are studied on ANT incorporated to BLM. They proved to be similar to those of so-called multiple conductance channel or permeability transition pore of inner mitochondrial membrane. The conductance of the single channel is as high as 2.2 nS. The channel fails to discriminate between K⁺, Na⁺, H⁺ and Cl⁻. Thus the obtained data are consistent with the assumption that native and modified ANT might function as an H⁺-specific conductor and as a permeability transition pore, respectively.