title: Spermine selectively inhibits high-conductance, but not low-conductance calcium-induced permeability transition pore.
abstract: The permeability transition pore (PTP) is a large channel of the mitochondrial inner membrane, the opening of which is the central event in many types of stress-induced cell death. PTP opening is induced by elevated concentrations of mitochondrial calcium. It has been demonstrated that spermine and other polyamines can delay calcium-induced swelling of isolated mitochondria, suggesting their role as inhibitors of the mitochondrial PTP. Here we further investigated the mechanism by which spermine inhibits the calcium-induced, cyclosporine A (CSA) -sensitive PTP by using three indicators: 1) calcium release from the mitochondria detected with calcium green, 2) mitochondrial membrane depolarization using TMRM, and 3) mitochondrial swelling by measuring light absorbance. We found that despite calcium release and membrane depolarization, indicative of PTP activation, mitochondria underwent only partial swelling in the presence of spermine. This was in striking contrast to the high-amplitude swelling detected in control mitochondria and in mitochondria treated with the PTP inhibitor CSA. We conclude that spermine selectively prevents opening of the high-conductance state, while allowing activation of the lower conductance state of the PTP. We propose that the existence of lower conductance, stress-induced PTP might play an important physiological role, as it is expected to allow the release of toxic levels of calcium, while keeping important molecules (e.g., NAD) within the mitochondrial matrix.
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
authors.forename: Pia A
authors.initials: PA
authors.lastname: Elustondo
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
authors.forename: Alexander
authors.initials: A
authors.lastname: Negoda
authors.affiliation: Department of Human Kinetics, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada.
authors.forename: Constance L
authors.initials: CL
authors.lastname: Kane
authors.affiliation: Department of Human Kinetics, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Kane
authors.affiliation: Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada. Electronic address: Evgeny.Pavlov@dal.ca.
authors.forename: Evgeny V
authors.initials: EV
authors.lastname: Pavlov
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D008928:Mitochondria / Q000187:drug effects / Q000473:pathology; D033681:Mitochondrial Membrane Transport Proteins / Q000187:drug effects*; D000083162:Mitochondrial Permeability Transition Pore; D008933:Mitochondrial Swelling / Q000187:drug effects; D009994:Osmolar Concentration; D051381:Rats; D017207:Rats, Sprague-Dawley; D013096:Spermine / Q000494:pharmacology*
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D013096:Spermine; D002118:Calcium
keywords: Calcium; Mitochondrial permeability transition pore; Spermine