Anion uniport in plant mitochondria is mediated by a Mg(2+)-insensitive inner membrane anion channel.
It has long been established that the inner membrane of plant mitochondria is permeable to Cl-. Evidence has also accumulated which suggests that a number of other anions such as Pi and dicarboxylates can also be transported electrophoretically. In this paper, we present evidence that anion uniport in plant mitochondria is mediated via a pH-regulated channel related to the so-called inner membrane anion channel (IMAC) of animal mitochondria. Like IMAC, the channel in potato mitochondria transports a wide variety of anions including NO3-, Cl-, ferrocyanide, 1,2,3-benzene-tricarboxylate, malonate, Pi, alpha-ketoglutarate, malate, adipate, and glucuronate. In the presence of nigericin, anion uniport is sensitive to the medium pH (pIC50 = 7.60, Hill coefficient = 2). In the absence of nigericin, transport rates are much lower and much less sensitive to pH, suggesting that matrix H+ inhibit anion uniport. This conclusion is supported by measurements of H+ flux which reveal that "activation" of anion transport at high pH by nigericin and at low pH by respiration is associated with an efflux of matrix H+. Other inhibitors of IMAC which are found to block anion uniport in potato mitochondria include propranolol (IC50 = 14 microM, Hill coefficient = 1.28), tributyltin (IC50 = 4 nmol/mg, Hill coefficient = 2.0), and the nucleotide analogs Erythrosin B and Cibacron Blue 3GA. The channel in plant mitochondria differs from IMAC in that it is not inhibited by matrix Mg2+, mercurials, or N,N'-dicyclohexylcarbodiimide. The lack of inhibition by Mg2+ suggests that the physiological regulation of the plant channel may differ from IMAC and that the plant IMAC may have functions such as a role in the malate/oxaloacetate shuttle in addition to its proposed role in volume homeostasis.
Beavis
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AD
Department of Pharmacology, Medical College of Ohio, Toledo 43699-0008.
Vercesi
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AE
D000818:Animals; D000838:Anions; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone / Q000494:pharmacology; D018118:Chloride Channels; D002712:Chlorides / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology*; D008565:Membrane Proteins / Q000187:drug effects / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D008930:Mitochondria, Liver / Q000378:metabolism*; D009550:Nigericin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D011198:Solanum tuberosum / Q000378:metabolism*; D014220:Trialkyltin Compounds / Q000494:pharmacology
D000838:Anions; D018118:Chloride Channels; D002712:Chlorides; D007473:Ion Channels; D008565:Membrane Proteins; D014220:Trialkyltin Compounds; C011559:tributyltin; D002258:Carbonyl Cyanide m-Chlorophenyl Hydrazone; D011433:Propranolol; D008274:Magnesium; D009550:Nigericin