title: Kinetic model for Ca2+-induced permeability transition in energized liver mitochondria discriminates between inhibitor mechanisms.
abstract: Cytotoxicity associated with pathophysiological Ca(2+) overload (e.g. in stroke) appears mediated by an event termed the mitochondrial permeability transition (mPT). We built and solved a kinetic model of the mPT in populations of isolated rat liver mitochondria that quantitatively describes Ca(2+)-induced mPT as a two-step sequence of pre-swelling induction followed by Ca(2+)-driven, positive feedback, autocatalytic propagation. The model was formulated as two differential equations, each directly related to experimental parameters (Ca(2+) flux/mitochondrial swelling). These parameters were simultaneously assessed using a spectroscopic approach to monitor multiple mitochondrial properties. The derived kinetic model correctly identifies a correlation between initial Ca(2+) concentration and delay interval prior to mPT induction. Within the model's framework, Ru-360 (a ruthenium complex) and Mg(2+) were shown to compete with the Ca(2+)-stimulated initiation phase of mPT induction, consistent with known inhibition at the phenomenological level of the Ca(2+) uniporter. The model further reveals that Mg(2+), but not Ru-360, inhibits Ca(2+)-induced effects on a downstream stage of mPT induction at a site distinct from the uniporter. The analytical approach was then applied to promethazine, an FDA-approved drug previously shown to inhibit both mPT and ischemia-reperfusion injury. Kinetic analysis revealed that promethazine delayed mPT induction in a manner qualitatively distinct from that of lower concentrations of Mg(2+). In summary, we have developed a kinetic model to aid in the quantitative characterization of mPT induction. This model is consistent with/informative about the biochemistry of several mPT inhibitors, and its success suggests that this kinetic approach can aid in the classification of agents or targets that modulate mPT induction.
authors.affiliation: Department of Neurosurgery, Brigham and Women's Hospital, Boston, Massachusetts 02115, USA.
authors.forename: Sergei V
authors.initials: SV
authors.lastname: Baranov
authors.forename: Irina G
authors.initials: IG
authors.lastname: Stavrovskaya
authors.forename: Abraham M
authors.initials: AM
authors.lastname: Brown
authors.forename: Alexei M
authors.initials: AM
authors.lastname: Tyryshkin
authors.forename: Bruce S
authors.initials: BS
authors.lastname: Kristal
mesh_terms: D000818:Animals; D002118:Calcium / Q000502:physiology*; D015220:Calcium Channels / Q000502:physiology; D002470:Cell Survival / Q000187:drug effects; D003433:Crosses, Genetic; D007425:Intracellular Membranes / Q000187:drug effects / Q000502:physiology*; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000502:physiology; D008297:Male; D008930:Mitochondria, Liver / Q000187:drug effects / Q000502:physiology*; D008933:Mitochondrial Swelling / Q000502:physiology; D008954:Models, Biological; D009243:NAD / Q000378:metabolism; D009249:NADP / Q000378:metabolism; D010539:Permeability; D011398:Promethazine / Q000494:pharmacology; D051381:Rats; D011914:Rats, Inbred BN; D011916:Rats, Inbred F344
chemical_list: D015220:Calcium Channels; D009243:NAD; D009249:NADP; D011398:Promethazine; D002118:Calcium