title: Regulation of monocarboxylate transporter 1 in skeletal muscle cells by intracellular signaling pathways.
abstract: Skeletal muscle is the major producer of lactic acid in the body, but its oxidative fibers also use lactic acid as a respiratory fuel. Monocarboxylate transporter (MCT) 1 has been suggested to play a major role in influx of L-lactic acid for oxidation. The regulation mechanism of MCT1 was characterized utilizing rhabdomyosarcoma cells as an in vitro skeletal muscle model. The uptake of L-lactic acid via MCT1 was studied in the presence of various intracellular regulatory pathways, including pathways mediated by protein kinases A, C and G (PKA, PKC and PKG), protein tyrosine kinase (PTK), and Ca2+/calmodulin modulators. The results showed that PKG-, PTK-, and Ca2+/calmodulin-mediated regulatory pathways play no role in the regulation of L-lactic acid uptake, but a role for PKC- and PKA-mediated pathways was apparent. Uptake of L-lactic acid appeared to be stimulated by phorbol 12-myristate 13-acetate (PMA, a PKC activator) via an increase in Vmax of transport processes with no alteration in Km. In parallel, PMA treatment also resulted in an increase in the level of MCT1 expression. On the other hand, exposure to 8-Br-cAMP, a cAMP analog, and to forskolin, an adenylyl cyclase activator, resulted in a significant decrease in L-lactic acid uptake. Additionally, 8-Br-cAMP reduced Vmax but not Km values. Parallel to the decrease in Vmax of L-lactic acid uptake, the level of MCT1 expression was decreased in response to incubation with 8-Br-cAMP. These results indicate the possible involvement of a PKC- and PKA-mediated pathway associated with expression of MCT1 and lactate transport.
authors.affiliation: Laboratory of Clinical Pharmaceutics & Therapeutics, Division of Pharmasciences, Faculty of Pharmaceutical Sciences, Hokkaido University, Sapporo, Japan.
authors.forename: Katsuya
authors.initials: K
authors.lastname: Narumi
authors.forename: Ayako
authors.initials: A
authors.lastname: Furugen
authors.forename: Masaki
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Sho
authors.initials: S
authors.lastname: Otake
authors.forename: Shirou
authors.initials: S
authors.lastname: Itagaki
authors.forename: Ken
authors.initials: K
authors.lastname: Iseki
mesh_terms: D001693:Biological Transport, Active / Q000502:physiology; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism / Q000502:physiology*; D019344:Lactic Acid / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000502:physiology*; D027501:Monocarboxylic Acid Transporters / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000166:cytology* / Q000378:metabolism / Q000502:physiology*; D011493:Protein Kinase C / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D012208:Rhabdomyosarcoma / Q000201:enzymology / Q000378:metabolism / Q000473:pathology; D027981:Symporters / Q000096:biosynthesis / Q000378:metabolism* / Q000502:physiology; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D017868:Cyclic AMP-Dependent Protein Kinases; D019344:Lactic Acid; D027501:Monocarboxylic Acid Transporters; D011493:Protein Kinase C; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1