A gated pathway for electrophoretic Na+ fluxes in rat liver mitochondria. Regulation by surface Mg2+.
Addition of EDTA to mitochondria incubated aerobically in a phosphate-supplemented medium containing Na+ ions results in activation of cation uptake which is accompanied by membrane depolarization and stimulation of respiration. The same results are obtained in media containing Li+ but not K+, indicating that this pathway for cation transport is selective. The activation of Na+ transport is not accompanied by changes of matrix Mg2+, indicating that cation transport is controlled by surface-bound rather than intramitochondrial Mg2+. Na+ transport in respiring mitochondria is competitively inhibited by Mg2+ with a Ki in the nanomolar range. A Na+ current can also be induced by a K+ diffusion potential in the absence of respiration. The K(+)-diffusion-driven Na+ current has the same magnitude in the absence or presence of inorganic phosphate, suggesting that Na+ transport is mediated by Na+ uniport rather than by electrogenic nNa+/H+ antiport with n greater than 1. Analysis of the flow/force relationship indicates that the putative Na+ uniporter has a conductance of about 0.2 nmol Na+ x mg protein-1 x min-1 x mV-1, and that it is active only when the membrane potential exceeds about 150 mV.
Bernardi
P
P
Consiglio Nazionale delle Ricerche Unit, University of Padova, Italy.
Angrilli
A
A
Azzone
G F
GF
D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D004492:Edetic Acid / Q000494:pharmacology; D004553:Electric Conductivity / Q000187:drug effects; D006863:Hydrogen-Ion Concentration; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D007700:Kinetics; D008094:Lithium / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects; D008930:Mitochondria, Liver / Q000187:drug effects / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers; D013053:Spectrophotometry
D002352:Carrier Proteins; D017923:Sodium-Hydrogen Exchangers; D008094:Lithium; D004492:Edetic Acid; D012964:Sodium; D008274:Magnesium; D011188:Potassium