Evidence for more than one Ca2+ transport mechanism in mitochondria.
The active transport and internal binding of the Ca2+ analogue Mn2+ by rat liver mitochondria were monitored with electron paramagnetic resonance. The binding of transported Mn2+ depended strongly on internal pH over the range 7.7-8.9. Gradients of free Mn2+ were compared with K+ gradients measured on valinomycin-treated samples. In the steady state, the electrochemical Mn2+ activity was larger outside than inside the mitochondria. The observed gradients of free Mn2+ and of H+ could not be explained by a single "passive" uniport or antiport mechanism of divalent cation transport. This conclusion was further substantiated by observed changes in steady-state Ca2+ and Mn2+ distributions induced by La3+ and ruthenium red. Ruthenium red reduced total Ca2+ or Mn2+ uptake, and both inhibitors caused release of divalent cation from preloaded mitochondria. A model is proposed in which divalent cations are transported by at least two mechanisms: (1) a passive uniport and (2) and active pump, cation antiport or anion symport. The former is more sensitive to La3+ and ruthenium red. Under energized steady-state conditions, the net flux of Ca2+ or Mn2+ is inward over (1) and outward over (2). The need for more than one transport system inregulating cytoplasmic Ca2+ is discussed.
D000085:Acetates / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007811:Lanthanum / Q000378:metabolism; D008345:Manganese / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000378:metabolism*; D008954:Models, Biological; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012430:Ruthenium Red / Q000494:pharmacology; D014634:Valinomycin / Q000494:pharmacology
D000085:Acetates; D012430:Ruthenium Red; D014634:Valinomycin; D008345:Manganese; D004533:Egtazic Acid; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D007811:Lanthanum; D011188:Potassium; D002118:Calcium