title: T3 increases lactate transport and the expression of MCT4, but not MCT1, in rat skeletal muscle.
abstract: Triiodothyronine (T3) regulates the expression of genes involved in muscle metabolism. Therefore, we examined the effects of a 7-day T3 treatment on the monocarboxylate transporters (MCT)1 and MCT4 in heart and in red (RG) and white gastrocnemius muscle (WG). We also examined rates of lactate transport into giant sarcolemmal vesicles and the plasmalemmal MCT1 and MCT4 in these vesicles. Ingestion of T3 markedly increased circulating serum T3 (P < 0.05) and reduced weight gain (P < 0.05). T3 upregulated MCT1 mRNA (RG +77, WG +49, heart +114%, P < 0.05) and MCT4 mRNA (RG +300, WG +40%). However, only MCT4 protein expression was increased (RG +43, WG +49%), not MCT1 protein expression. No changes in MCT1 protein were observed in any tissue. T3 treatment doubled the rate of lactate transport when vesicles were exposed to 1 mM lactate (P < 0.05). However, plasmalemmal MCT4 was only modestly increased (+13%, P < 0.05). We conclude that T3 1) regulates MCT4, but not MCT1, protein expression and 2) increases lactate transport rates. This latter effect is difficult to explain by the modest changes in plasmalemmal MCT4. We speculate that either the activity of sarcolemmal MCTs has been altered or else other MCTs in muscle may have been upregulated.
authors.affiliation: Department of Kinesiology, University of Waterloo, Ontario, Canada.
authors.forename: Yuxiang
authors.initials: Y
authors.lastname: Wang
authors.forename: Mio
authors.initials: M
authors.lastname: Tonouchi
authors.forename: Dragana
authors.initials: D
authors.lastname: Miskovic
authors.forename: Hideo
authors.initials: H
authors.lastname: Hatta
authors.forename: Arend
authors.initials: A
authors.lastname: Bonen
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism*; D008297:Male; D027501:Monocarboxylic Acid Transporters / Q000235:genetics* / Q000378:metabolism; D009124:Muscle Proteins / Q000235:genetics* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D012508:Sarcolemma / Q000378:metabolism; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D019344:Lactic Acid; D027501:Monocarboxylic Acid Transporters; D009124:Muscle Proteins; D012333:RNA, Messenger; D027981:Symporters; D014284:Triiodothyronine; D000099233:Monocarboxylate Transport Protein 1; C516342:Slc16a3 protein, rat