title: Not all mitochondrial carrier proteins support permeability transition pore formation: no involvement of uncoupling protein 1.
abstract: The mPTP (mitochondrial permeability transition pore) is a non-specific channel that is formed in the mitochondrial inner membrane in response to several stimuli, including elevated levels of matrix calcium. The pore is proposed to be composed of the ANT (adenine nucleotide translocase), voltage-dependent anion channel and cyclophilin D. Knockout studies, however, have demonstrated that ANT is not essential for permeability transition, which has led to the proposal that other members of the mitochondrial carrier protein family may be able to play a similar function to ANT in pore formation. To investigate this possibility, we have studied the permeability transition properties of BAT (brown adipose tissue) mitochondria in which levels of the mitochondrial carrier protein, UCP1 (uncoupling protein 1), can exceed those of ANT. Using an improved spectroscopic assay, we have quantified mPTP formation in de-energized mitochondria from wild-type and Ucp1KO (Ucp1-knockout) mice and assessed the dependence of pore formation on UCP1. When correctly normalized for differences in mitochondrial morphology, we find that calcium-induced mPTP activity is the same in both types of mitochondria, with similar sensitivity to GDP (approximately 50% inhibited), although the portion sensitive to cyclosporin A is higher in mitochondria lacking UCP1 (approximately 80% inhibited, compared with approximately 60% in mitochondria containing UCP1). We conclude that UCP1 is not a component of the cyclosporin A-sensitive mPTP in BAT and that playing a role in mPTP formation is not a general characteristic of the mitochondrial carrier protein family but is, more likely, restricted to specific members including ANT.
authors.affiliation: MRC Mitochondrial Biology Unit, Hills Road, Cambridge CB2 0XY, UK. pgc@mrc-mbu.cam.ac.uk
authors.forename: Paul G
authors.initials: PG
authors.lastname: Crichton
authors.forename: Nadeene
authors.initials: N
authors.lastname: Parker
authors.forename: Antonio J
authors.initials: AJ
authors.lastname: Vidal-Puig
authors.forename: Martin D
authors.initials: MD
authors.lastname: Brand
mesh_terms: D002001:Adipose Tissue, Brown / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D000081406:Peptidyl-Prolyl Isomerase F; D021983:Cyclophilins / Q000378:metabolism; D016572:Cyclosporine / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004896:Erythritol / Q000494:pharmacology; D005260:Female; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000378:metabolism*; D000226:Mitochondrial ADP, ATP Translocases / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D000083162:Mitochondrial Permeability Transition Pore; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D008933:Mitochondrial Swelling / Q000187:drug effects; D016133:Polymerase Chain Reaction; D013997:Time Factors; D000071256:Uncoupling Protein 1; D050994:Voltage-Dependent Anion Channels / Q000378:metabolism
chemical_list: D000081406:Peptidyl-Prolyl Isomerase F; D007473:Ion Channels; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D024101:Mitochondrial Proteins; C000631446:PPIF protein, mouse; C000604372:Ucp1 protein, mouse; D000071256:Uncoupling Protein 1; D050994:Voltage-Dependent Anion Channels; D016572:Cyclosporine; D000226:Mitochondrial ADP, ATP Translocases; D021983:Cyclophilins; D004896:Erythritol; D002118:Calcium