The effects of manganese on the solute content of rat-liver mitochondria

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Abstract
At 20[degree], mM MnCl2 decreased the loss of UV-light-absorbing nucleotide-like substances and protein from mitochondria suspended in 0.25 [image] sucrose. Mn did not affect nucleotide loss when the suspending medium was 0.1 [image] KC1 plus 0.05 [image] sucrose. In either medium, m[image] MnCl2 maintained the mitochondria at a higher dry weight than in its absence. Mitochondria suspended in 0.25 [image] sucrose and m[image] MnCl2 took up Mn at a high rate at 0[degree], reaching about 25 m-moles/kg dry weight of mitochondria. The uptake was increased when the concentration of MnCl2 in the medium was increased, but not proportionally. With 5 m[image] MnCl2 the uptake reached 60 m-moles/kg dry weight. The loss of water from the mitochondria was higher in the presence of 5 m[image] MnCl2 than with m[image]. The uptake of Mn by mitochondria suspended in 0.1 [image] KC1, 0.05 [image] sucrose and m[image] MnCl2 at 0[degree] was about 1.5 times as fast as in 0.25 [image] sucrose. A further increase of 1.5 times in the rate of uptake occurred when the temperature was raised to 20[degree]. The total uptake reached 81 m-moles/kg dry weight. The uptake of Mn was about the same when the MnCl2 was added after the mitochondria had equilibrated with the KCl-sucrose mixture. After incubation for 15 minutes in nitrogen at 25[degree], the uptake of Mn of mitochondria suspended in 0.1 [image] KC1 plus 0.05 [image] sucrose was only 69% of the uptake in oxygen. Further incubation caused an increase of the Mn content of the mitochondria in oxygen but not of those in nitrogen. The uptake of Mn by mitochondria suspended in 0.25 [image] sucrose and m[image] MnCl2 was completely inhibited by 1.5 m[image] ethylenediaminetetra-acetic acid. The addition of MnCl2 to a mitochondrial suspension caused a fall in the pH of the suspension of as much a 1 pH unit. The change of pH was increased by an increase of Mn concentration and by the presence of KC1 in the medium and decreased by raising the temperature above 0[degree]. In 0.25 [image] sucrose solution, between 60 and 90% of the uptake of Mn could be accounted for by the liberation of H+ ions. Mn maintained the impermeability of the mitochondrial membrane to Cl. At 0[degree], m[image] MnCl2 displaced about 1/3 of the endogenous Mg content and about 1> of the endogenous Ca content Transfer of mitochondria from 0.25 [image] sucrose to 0.1 [image] KC1 plus 0.05 [image] sucrose caused a loss of about half the endogenous Mg, but no loss of the endogenous Ca. Mn prevented the loss of Mg at 0[degree] which occurs in the salt-sucrose mixture. The most effective concentration was 1.5 m[image]. Incubation of mitochondria at 24[degree] in 0.1 [image] KC1, 0.05 [image] sucrose and 1.5 m[image] MnCl2 after they had lost endogenous Mg at 0[degree], resulted in an uptake of most of the Mg lost. The loss of mitochondrial phosphate that occurred in 0.1 [image] KC1 plus 0.05 [image] sucrose at 0[degree] was abolished by the addition of 1.5 m[image] MnCl2 to the medium. Incubation at 24[degree], in the Mn-containing medium, of mitochondria which had already lost phosphate resulted in a restoration of the phosphate content. In sucrose or saline media at 0[degree] or at 25[degree] the presence of m[image] MnCl2 resulted in a lower water content of mitochondria than occurred in its absence. The mode of action of Mn, in the stabilization of mitochondria is discussed.