Inner membrane anion channel and dicarboxylate carrier in brown adipose tissue mitochondria.
In brown adipose tissue mitochondria, the anion transport proteins should respond to regulatory mechanisms controlling the thermogenic or resting state. We re-evaluated the role of transport of organic/metabolite anions in these mitochondria, namely with regards to delta pH-regulation and substrate specificity. Valinomycin-induced osmotic swelling in potassium salts indicated by light scattering either directly on a fluorometer, or as the reciprocal absorbance, was used to characterize the anion uniport. A delta pH "jump" was thus created in respiring mitochondria and the delta pH-driven transport was studied. The two major features are reported: (1) existence of the inner membrane anion channel exhibiting the same full spectrum of anion and inhibitor specificity as in liver; and (2) existence of dicarboxylate carrier, so far disputed in brown adipose tissue mitochondria. The inner membrane anion channel was activated either by elevating delta pH in respiring mitochondria or by depleting matrix Mg2+ at alkaline pH. Dicarboxylate carrier was activated by elevated delta pH under conditions when the channel was blocked. A specific delta pH regulation could explain this activation and silence of the carrier in early studies. In conclusion, wide substrate specificity makes the inner membrane anion channel suitable for the regulation of volume homeostasis and a feed-back control between the delta psi-driven and the delta pH-driven transport. The delta pH-activated dicarboxylate carrier is essential in the coupled state for malate uptake which enables fatty acid synthesis, while, in the uncoupled state, inaccessibility of dicarboxylates favors oxidation of fatty acids or pyruvate.
Jezek
P
P
Department of Membrane Transport Biophysics, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
Borecký
J
J
D002001:Adipose Tissue, Brown / Q000378:metabolism* / Q000648:ultrastructure; D000818:Animals; D017920:Antiporters / Q000378:metabolism*; D001692:Biological Transport; D006224:Cricetinae; D003998:Dicarboxylic Acids / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000648:ultrastructure*; D007473:Ion Channels / Q000378:metabolism*; D008647:Mesocricetus; D008928:Mitochondria / Q000378:metabolism*
D017920:Antiporters; D003998:Dicarboxylic Acids; D007473:Ion Channels