title: Physical and functional association of lactate dehydrogenase (LDH) with skeletal muscle mitochondria.
abstract: The intracellular lactate shuttle hypothesis posits that lactate generated in the cytosol is oxidized by mitochondrial lactate dehydrogenase (LDH) of the same cell. To examine whether skeletal muscle mitochondria oxidize lactate, mitochondrial respiratory oxygen flux (JO2) was measured during the sequential addition of various substrates and cofactors onto permeabilized rat gastrocnemius muscle fibers, as well as isolated mitochondrial subpopulations. Addition of lactate did not alter JO2. However, subsequent addition of NAD(+) significantly increased JO2, and was abolished by the inhibitor of mitochondrial pyruvate transport, α-cyano-4-hydroxycinnamate. In experiments with isolated subsarcolemmal and intermyofibrillar mitochondrial subpopulations, only subsarcolemmal exhibited NAD(+)-dependent lactate oxidation. To further investigate the details of the physical association of LDH with mitochondria in muscle, immunofluorescence/confocal microscopy and immunoblotting approaches were used. LDH clearly colocalized with mitochondria in intact, as well as permeabilized fibers. LDH is likely localized inside the outer mitochondrial membrane, but not in the mitochondrial matrix. Collectively, these results suggest that extra-matrix LDH is strategically positioned within skeletal muscle fibers to functionally interact with mitochondria.
authors.affiliation: From the Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2 and.
authors.forename: Pia A
authors.initials: PA
authors.lastname: Elustondo
authors.affiliation: the Departments of Human Kinetics and.
authors.forename: Adrienne E
authors.initials: AE
authors.lastname: White
authors.affiliation: the Departments of Human Kinetics and.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Hughes
authors.affiliation: Psychology, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
authors.forename: Karen
authors.initials: K
authors.lastname: Brebner
authors.affiliation: From the Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2 and.
authors.forename: Evgeny
authors.initials: E
authors.lastname: Pavlov
authors.affiliation: the Departments of Human Kinetics and. Electronic address: dkane@stfx.ca.
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Kane
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D003373:Coumaric Acids / Q000494:pharmacology; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D019344:Lactic Acid / Q000378:metabolism; D008931:Mitochondria, Muscle / Q000378:metabolism*; D051336:Mitochondrial Membranes / Q000201:enzymology*; D009124:Muscle Proteins / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000201:enzymology*; D010084:Oxidation-Reduction / Q000187:drug effects; D010101:Oxygen Consumption / Q000187:drug effects / Q000502:physiology; D019289:Pyruvic Acid / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D003373:Coumaric Acids; D009124:Muscle Proteins; C007175:alpha-cyano-4-hydroxycinnamate; D019344:Lactic Acid; D019289:Pyruvic Acid; D007770:L-Lactate Dehydrogenase
keywords: Immunohistochemistry; Lactate Shuttle; Lactic Acid; Mitochondrial Metabolism; NAD; Pyruvate; Respiration; Respiratory Chain; Respirometry; Skeletal Muscle Metabolism