Feldkamp T, Park JS, Pasupulati R, Amora D, Roeser NF, Venkatachalam MA, Weinberg JM. Regulation of the mitochondrial permeability transition in kidney proximal tubules and its alteration during hypoxia/reoxygenation. Am J Physiol Renal Physiol 297: F1632-F1646, 2009. First published September 9, 2009 doi:10.1152/ajprenal.00422.2009.-Development of the mitochondrial permeability transition (MPT) can importantly contribute to lethal cell injury from both necrosis and apoptosis, but its role varies considerably with both the type of cell and type of injury, and it can be strongly opposed by the normally abundant endogenous metabolites ADP and Mg 2ϩ . To better characterize the MPT in kidney proximal tubule cells and assess its contribution to injury to them, we have refined and validated approaches to follow the process in whole kidney proximal tubules and studied its regulation in normoxic tubules and after hypoxia-reoxygenation (H/R). Physiological levels of ADP and Mg 2ϩ greatly decreased sensitivity to the MPT. Inhibition of cyclophilin D by cyclosporine A (CsA) effectively opposed the MPT only in the presence of ADP and/or Mg 2ϩ . Nonesterified fatty acids (NEFA) had a large role in the decreased resistance to the MPT seen after H/R irrespective of the available substrate or the presence of ADP, Mg 2ϩ , or CsA, but removal of NEFA was less effective at restoring normal resistance to the MPT in the presence of electron transport complex I-dependent substrates than with succinate. The data indicate that the NEFA accumulation that occurs during both hypoxia in vitro and ischemic acute kidney injury in vivo is a critical sensitizing factor for the MPT that overcomes the antagonistic effect of endogenous metabolites and cyclophilin D inhibition, particularly in the presence of complex I-dependent substrates, which predominate in vivo.acute kidney injury; membrane potential; mitochondria A VARIETY OF INSULTS can produce a sustained increase of the permeability of the inner mitochondrial membrane that prevents it from maintaining the transmembrane ion gradients necessary for energy conservation. The process, now most commonly called the mitochondrial permeability transition (MPT), is characterized by loss of inorganic and small organic matrix solutes and mitochondrial swelling. Considerable evidence supports the concept that the MPT results from reversible opening of an ϳ3-nm-diameter pore with a size exclusion limit of ϳ1,500 Da that is frequently termed the permeability transition pore (PTP) (5,7,32,34,36,39,40,48,69,75,82). There also is evidence for more selective substates of the MPT (10,13,40,46,51) and for its transient opening under physiological conditions (42,70). In isolated mitochondria, the development of the PTP is regulated by matrix divalent cations, mitochondrial membrane potential (⌬⌿ m ), matrix pH, ADP, and NAD(P)H redox state (5,32,34,36,39,48,82). Opening of the pore can be prevented and reversed by cyclosporine A (CsA), via inhibition by CsA of the binding of mitochondrial matrix cyclophilin...
