Electrical currents associated with nucleotide transport by the reconstituted mitochondrial ADP/ATP carrier

Nickolay Brustovetsky, Anja Becker, Martin Klingenberg, Ernst Bamberg

Research output: Contribution to journalArticle

39 Scopus citations

Abstract

The electrophoretic export of ATP against the impart of ADP in mitochondria bridges the intra- versus extramitochondrial ATP potential gap. Here we report that the electrical nature of the ADP/ATP exchange by the mitochondrial ADP/ATP carrier (AAC) can be directly studied by measuring the electrical currents via capacitive coupling of AAC-containing vesicles on a planar lipid membrane. The currents were induced by the rapid liberation of ATP or ADP with UV flash photolysis from caged nucleotides. Six different transport modes of the AAC were studied: heteroexchange with either ADP or ATP inside the vesicles, initiated by photolysis of caged ATP or ADP; homoexchange with ADP(es)/ADP(in) or ATP(ex)/ATP(in); and caged ADP or ATP with unloaded vesicles. The heteroexchange produced the largest currents with the longest duration in line with the electrical charge difference ATP4- versus ADP3-. Surprisingly, also in the homoexchange and with unloaded vesicles, small currents were measured with shorter duration. In all three modes with caged ATP, a negative charge moved into the vesicles and with caged ADP it moved out of the vesicles. All currents were completely inhibited by a mixture of the inhibitors of the AAC, carboxyatractyloside and bongkrekate, which proves that the currents are exclusively due to AAC function. The observed charge movements in the heteroexchange system agree with the prediction from transport studies in mitochondria and reconstituted vesicles. The unexpected charge movements in the homoexchange or unloaded systems are interpreted to reveal transmembrane rearrangements of charged sites in the AAC when occupied with ADP or ATP. The results also indicate that not only ATP4- but also ADP3- contribute, albeit in opposite direction, to the electrical nature of the ADP/ATP exchange, which is at variance with former conclusions from biochemical transport studies. These measurements open up new avenues of studying the electrical interactions of ADP and ATP with the AAC.

Original languageEnglish (US)
Pages (from-to)664-668
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Volume93
Issue number2
DOIs
StatePublished - Jan 23 1996

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Keywords

  • caged nucleotides
  • capacitive currents
  • phospholipid bilayer

ASJC Scopus subject areas

  • General

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