EFFECT OF BUTYLHYDROXYTOLUENE AND RELATED-COMPOUNDS ON PERMEABILITY OF THE INNER MITOCHONDRIAL-MEMBRANE

Mitochondrial inner membrane contains a latent pore (PTP) that when op ened uncouples mitochondrial energy transduction and allows rapid equi libration of low-molecular-weight solutes between the matrix and exter ior. Based on sensitivity of the PTP to well-known free radical scaven ger butylhydroxytoluene (BHT), it has been proposed that increased ste ady-state level of oxygen radicals, and subsequent radical attack of p roteins and lipids, is a central event in activation of this pore (Nov gorodov et al., J. Bioenerg. Biomembr. 19, 191-202, 1987; Carbonera an d Azzone, Biochim. Biophys. Acta 943, 245-255, 1988). Present studies revealed that DBT, a derivative of BHT devoid of radical scavenging ac tivity, exerts an analogous effect on the permeability of the inner me mbrane. Inhibition of the Ca2+-induced PTP opening is essentially comp lete at dose range of 50-60 nmol/mg protein with IC50 values of about 32 and 23 nmol/mg protein for DBT and BHT, respectively, Electron micr oscopy and osmotic experiments utilizing polyethylene glycols with dif ferent Stokes radii showed that the apparent lack of inhibition seen a t high concentrations of these compounds results from cyclosporin A- a nd Ca2+- insensitive pore formation in the inner membrane. Experiments employing antioxidants with similar structure but dissimilar hydropho bicity provided evidence for localization of the antioxidant binding s ites within the hydrophobic zone of the inner membrane or in the matri x space. The data obtained do not refute the notion that oxygen radica ls modulate the PTP, but rather indicate that BHT operates independent ly of its free radical scavenging activity. Overall, the sensitivity t o BHT and other antioxidants is not always a reliable criterion for th e involvement of free radical reactions in the processes under study. (C) 1997 Academic Press.