Evidence for the allosteric regulation of the mitochondrial K+/H+ antiporter by matrix protons.
It is well accepted that the mitochondrial K+/H+ antiporter is regulated by matrix Mg2+; however, this is not the only factor controlling its activity. The precise conditions used to deplete divalent cations have profound effects on the subsequent activity of the antiporter in a KOAc assay medium. Examination of the proton fluxes during both pretreatment and subsequent assay of K+/H+ antiport reveals that differences in K+/H+ antiport activity correlate very well with differences in matrix pH. Thus, inhibition of the K+/H+ antiporter following depletion of Mg2+ appears to result from inhibition by matrix protons. To test this hypothesis, we have examined the effect of modulating matrix pH in three different ways on the activity of the K+/H+ antiporter: 1) lowering the pH of the K+ pretreatment medium to 6.7 leads to inactivation of the K+/H+ antiporter; 2) adding NH4+ to the assay medium eliminates the lag in activity induced by depleting Mg2+ in a pretreatment medium containing NH4+; 3) permitting mitochondria to respire in a tetraethylammonium(+)-containing pretreatment medium activates the K+/H+ antiporter. Each one of these procedures leads to a change in matrix pH and an effect on K+/H+ antiport which appears to require regulation of the K+/H+ antiporter by matrix protons. This finding is not only physiologically significant but also provides a useful definition of conditions required for unmasking the K+/H+ antiporter in a reproducible manner.
Beavis
A D
AD
Department of Pharmacology, Medical College of Ohio, Toledo 43699-0008.
Garlid
K D
KD
D000085:Acetates / Q000494:pharmacology; D000494:Allosteric Regulation; D000001:Calcimycin / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism / Q000494:pharmacology; D027961:Potassium-Hydrogen Antiporters; D011506:Proteins / Q000378:metabolism*; D011522:Protons; D019789:Tetraethylammonium; D013757:Tetraethylammonium Compounds / Q000494:pharmacology
D000085:Acetates; D002352:Carrier Proteins; D027961:Potassium-Hydrogen Antiporters; D011506:Proteins; D011522:Protons; D013757:Tetraethylammonium Compounds; D000001:Calcimycin; D019789:Tetraethylammonium; D011188:Potassium