Nutritional effects on mitochondrial bioenergetics. Alterations in calcium uptake by rat liver mitochondria.
The uptake of Ca2+ by energized liver mitochondria was compared in normal fed as well as in protein-energy malnourished rats. In the presence of phosphate, mitochondria obtained from both groups were able to accumulate Ca2+ from the suspending medium and eject H+ during oxidation of common substrates which activate different segments of the respiratory chain. The rate of Ca2+ uptake was significantly lower in mitochondria from protein-energy malnourished rats. The rates of oxygen consumption and H+ ejection were decreased by 20-30% during oxidation of substrates at the three coupling sites. Similarly, mitochondria from protein-energy malnourished rats exhibit a 34% decrease in the maximal rate of Ca2+ uptake and a 25% lower capacity for Ca2+ load. The stoichiometric relationship of Ca2+/2e- remained unaffected. In steady state, with succinate as a substrate in the presence of rotenone and N-ethylmaleimide, mitochondria from normal fed and protein-energy malnourished rats showed a similar rate of Ca2+ uptake. Furthermore in both groups the stoichiometry of the H+/O ratio was close to 8.0 (H+/site ratio close to 4.0), and of Ca2+/site was close to 2.0. The diminished rate of Ca2+ uptake observed in mitochondria from protein-energy malnourished rats could be explained on the basis of a depressed rate of electron transport in the respiratory chain rather than by an effect at the level of the Ca2+ or H+ transport mechanism per se.
Ferreira
J
J
Department of Biochemistry, Faculty of Medicine, University of Chile, Santiago.
Gil
L
L
D000818:Animals; D001665:Binding Sites; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism* / Q000493:pharmacokinetics; D004579:Electron Transport; D004734:Energy Metabolism; D005033:Ethylmaleimide / Q000494:pharmacology; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D010101:Oxygen Consumption; D010710:Phosphates / Q000494:pharmacology; D011488:Protein Deficiency / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012402:Rotenone / Q000494:pharmacology; D013386:Succinates / Q000494:pharmacology
D010710:Phosphates; D013386:Succinates; D012402:Rotenone; D005033:Ethylmaleimide; D002118:Calcium