Mg2+ inhibition of Na2+-stimulated Ca2+ release from brain mitochondria.

Magnesium has been shown to modulate the Na+-stimulated release of Ca2+ (Na/Ca exchange) from brain mitochondria. The presence of 5 mM MgCl2 extramitochondrially inhibits the Na/Ca exchange as much as 70%. Additionally, Na+-stimulated Ca2+ release is enhanced by the presence of divalent chelators, this stimulation also being inhibited by the addition of excess Mg2+. The inhibitory effect of Mg2+ and the enhancement by chelating agents were both reversible. Heart mitochondria exhibit a similar enhancement of Na/Ca exchange by chelators and inhibition by MgCl2, though not as pronounced.