title: K+-H+ exchange and volume homeostasis in brown adipose tissue mitochondria.
abstract: K+-H+ exchange activity in hamster brown adipose tissue mitochondria is activated following depletion of matrix Mg2+ with the divalent cation ionophore A23187. Quinine inhibits K+-H+ exchange reversibly with an I50 of 22 microM, whereas mild treatment with N,N'-dicyclohexylcarbodiimide (DCCD) inhibits this activity irreversibly. In an attempt to label and identify the K+-H+ antiporter protein, brown adipose tissue mitochondria were incubated with [14C]DCCD and subjected to denaturing polyacrylamide gel electrophoresis and fluorography. We observed a labeled band of relative mol wt, 78,000, which satisfies criteria established in rat liver mitochondria for the identification of this carrier (W. H. Martin et al., J. Biol. Chem. 259: 2062-2065, 1984). Thus Mg2+ and quinine each protect the K+-H+ exchanger against both inhibition and binding by DCCD. Volume homeostasis in brown adipose tissue mitochondria, as in other mitochondria, requires a balance between K+ influx and efflux. We propose that regulation of the K+-H+ antiporter, the primary K+ efflux mechanism, plays a major role in this process.
mesh_terms: D002001:Adipose Tissue, Brown / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism; D006224:Cricetinae; D004024:Dicyclohexylcarbodiimide / Q000378:metabolism / Q000494:pharmacology; D006706:Homeostasis; D006859:Hydrogen / Q000378:metabolism*; D007474:Ion Exchange; D008274:Magnesium / Q000494:pharmacology; D008647:Mesocricetus; D008928:Mitochondria / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism*; D027961:Potassium-Hydrogen Antiporters; D011803:Quinine / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D027961:Potassium-Hydrogen Antiporters; D004024:Dicyclohexylcarbodiimide; D006859:Hydrogen; D011803:Quinine; D008274:Magnesium; D011188:Potassium