IS ZN2+ TRANSPORTED BY THE MITOCHONDRIAL CALCIUM UNIPORTER

Zinc ions were found to inhibit Ca2+ uptake by rat liver mitochondria driven by succinate respiration but not that by a valinomycin-induced membrane potential. Zn2+ at 1 mu M or higher concentrations induced a lowering of the membrane potential under the former but not the latter conditions. It is concluded that it is the lowered membrane potential in the presence of Zn2+ that reduces the rate of respiration-driven C a2+. Ruthenium red was found to inhibit the uptake of Zn2+ but had no influence on its action upon the membrane potential. Zn2+ did not affe ct the Ruthenium red-insensitive Ca2+ efflux. Ca2+ stimulated the upta ke of Zn2+. It is concluded that Zn2+ may be transported by the mitoch ondrial calcium uniporter but that it may have access to sites require d for inhibition of respiration by other routes.