Quantitative evaluation of the effects of mitochondrial permeability transition pore modifiers on accumulation of calcium phosphate: comparison of rat liver and brain mitochondria

Mitochondria play a critical role in some forms of apoptosis, and the Ca2+-dependent permeability transition (PT) is a key initiator of this process. We quantitatively examined major control mechanisms of PT in rat brain (RBM) and liver (RLM) mitochondria. Compared with RLM, RBM were less sensitive to cyclosporin A (CsA), but the combined action of CsA + ADP was much more pronounced in RBM. Carboxyatractyloside abrogated the effects of all mPTP inhibitors in RBM but not in RLM, where the effects of CsA were not reduced. Estimated H+/Ca2+ ratios were 0.81 ± 0.01 for RLM and 0.84 − 0.93 for RBM, suggesting that Ca2+ and Pi were sequestered in the matrix as CaHPO4 and Ca3(PO4)2 salts, and that RBM sequester more CaPi as the least soluble salt. We conclude that: (1) RBM and RLM differ in their baseline behavior of the PT and in their responses to PT modifiers, and (2) PT modifiers can be functionally divided into those which directly affect the mitochondrial PT pore and are not energy-dependent (CsA, free Ca2+, ADPex, and Mg2+), and those which affect the energy-dependent calcium phosphate sequestration process (ADPmt, CATR, local anesthetics). We also conclude that ANT affects PT by changing mitochondrial capacity for energization.