Magnesium Transport by Brain Mitochondria: Energy Requirement and Dependence on Ca2+ Fluxes

Abstract: The association of Mg²⁺ ions with mitochondria isolated from guinea pig cerebral cortex is investigated and resolved into two components, that bound to the surface of both the outer and the inner membranes and that transported into the mitochondrial matrix. When rotenone-treated mitochondria are preincubated in a Mg²⁺ -containing medium, Mg²⁺ binding can be measured and actual Mg²⁺ transport determined after the addition of succinate. Mg²⁺ uptake as well as retention within mitochondria is an energy-dependent process linked to substrate oxidation. EGTA completely prevents Mg²⁺ uptake, while the Ca²⁺ uniporter inhibitor Ruthenium Red, along with prevention of Mg²⁺ uptake, induces a slow efflux of accumulated Mg²⁺ ions. These findings suggest that both inward and outward Mg²⁺ movements follow Ca²⁺ fluxes across the mitochondrial membrane. Modulation of Mg²⁺ movements by mitochondria is therefore suggested to occur within nerve terminals.