Picard 2008 Am J Physiol Regul Integr Comp Physiol
| Picard M, Csukly K, Robillard ME, Godin R, Ascah A, Bourcier-Lucas C, Burelle Y (2008) Resistance to Ca2+-induced opening of the permeability transition pore differs in mitochondria from glycolytic and oxidative muscles. Am J Physiol Regul Integr Comp Physiol 295:R659-68. doi: 10.1152/ajpregu.90357.2008 |
Picard M, Csukly K, Robillard ME, Godin R, Ascah A, Bourcier-Lucas C, Burelle Y (2008) Am J Physiol Regul Integr Comp Physiol
Abstract: This study determined whether susceptibility to opening of the permeability transition pore (PTP) varies according to muscle phenotype represented by the slow oxidative soleus (Sol) and superficial white gastrocnemius (WG). Threshold for Ca2+-induced mitochondrial Ca2+ release following PTP opening was determined with a novel approach using permeabilized ghost myofibers. Threshold values for PTP opening were approximately threefold higher in fibers from WG compared with those from Sol (124±47 vs. 30.4±6.8 pmol Ca2+/mU citrate synthase). A similar phenomenon was also observed in isolated mitochondria (threshold: 121±60 vs. 40±10 nmol Ca2+/mg protein in WG and Sol), indicating that this was linked to differences in mitochondrial factors between the two muscles. The resistance of WG fibers to PTP opening was not related to the expression of putative protein modulators (cyclophilin D, adenylate nucleotide translocator-1, and voltage-dependent anion channels) or to difference in respiratory properties and occurred despite the fact that production of reactive oxygen species, which promote pore opening, was higher than in the Sol. However, endogenous matrix Ca2+ measured in mitochondria isolated under resting baseline conditions was approximately twofold lower in the WG than in the Sol (56±4 vs. 111±11 nmol/mg protein), which significantly accounted for the resistance of WG. Together, these results reveal fiber type differences in the sensitivity to Ca2+-induced PTP opening, which may constitute a physiological mechanism to adapt mitochondria to the differences in Ca2+ dynamics between fiber types.
• Bioblast editor: Gnaiger E
Labels: MiParea: Respiration, Comparative MiP;environmental MiP
Stress:Permeability transition Organism: Rat Tissue;cell: Skeletal muscle Preparation: Permeabilized tissue, Isolated mitochondria
Regulation: Calcium
Selected quotes and comments
- After the addition of mitochondria, Ca2+-pulses (83 nmol/mg protein) were addedat 2-min intervals until mitochondrial Ca2+-release caused by opening of the PTP was observed. CRC was calculated as the cumulative amount of Ca2+ taken by mitochondria before Ca2+-release.
- Comment: Calcium retention capacity CRC is in this approach not 'the cumulative amount of Ca2+ taken by mitochondria', if no correction is made for an increase of Ca2+ concentration in the medium before opening of the PTP.
- After the addition of fibers and respiratory substrates, a single pulse of 20 nmol of Ca2+ was added. CRC was taken as the total amount of Ca2+ accumulated by mitochondria before Ca2+ release caused by PTP opening. CRC values were expressed per milligram of dry fiber weight and by unit of CS. [Ca2+] in the cuvette was calculated from a standard curve relating [Ca2+] to the fluorescence of Ca-green.
- Comment: CRC obtain in this approach is actually calcium uptake capacity. 20 nmol Ca2+ added to a 600 µL cuvette yields 30 mmol/L Ca2+. When [Ca2+] subtracted from this initial concentration is subtracted, then actual calcium uptake capacity is obtained when expressed by a mitochondrial marker. Oxygen concentration was not monitored or controlled in the cuvette during these measurements.
