title: Effect of a myocardial volume overload on lactate transport in skeletal muscle sarcolemmal vesicles.
abstract: This study sought to determine the effect of a myocardial volume overload (MVO) on sarcolemmal (SL) lactate (La(-)) transport and the aerobic profile of skeletal muscle. SL vesicles were obtained from female rats 10 wk after either a MVO was induced by creation of an infrarenal fistula (n = 10), or sham surgeries were performed (n = 11). Influx of (14)C-labeled L(+)-La(-) was measured at various unlabeled La(-) concentrations under zero-trans conditions. La(-) transport kinetics were determined using a Michaelis-Menten equation with an added linear component to discriminate between carrier-mediated and diffusional transport. Although heart and lung weights were significantly increased (P < 0.0001) in the MVO group, left ventricular function was only modestly altered (P < 0.05). A significant reduction in type I myosin heavy chain (MHC) in the soleus and a strong trend (P = 0.06) for a reduced type IIx MHC in the plantaris were observed in MVO rats, but no differences in citrate synthase activity or monocarboxylate transporter proteins (MCT)-1 expression were noted in any muscle. Carrier-mediated La(-) influx into SL vesicles was similar between sham and MVO (K(m) = 12 +/- 1 and 18 +/- 3 mM; apparent V(max) = 772 +/- 99 and 827 +/- 80 nmol. mg(-1). min(-1), respectively). Total influx at 100 mM was lower in MVO, and this was due to a 30% reduction in membrane diffusion. In conclusion, a 10-wk MVO did not alter MCT-mediated La(-) transport or protein expression but was associated with modest changes in myofibrillar proteins and impaired SL diffusive properties.
authors.affiliation: Department of Health and Human Performance, Auburn University, Auburn University College of Veterinary Medicine, Auburn, Alabama 36849, USA.
authors.forename: W G
authors.initials: WG
authors.lastname: Aschenbach
authors.forename: G L
authors.initials: GL
authors.lastname: Brower
authors.forename: R J
authors.initials: RJ
authors.lastname: Talmadge
authors.forename: J L
authors.initials: JL
authors.lastname: Dobson
authors.forename: L B
authors.initials: LB
authors.lastname: Gladden
mesh_terms: D000818:Animals; D002306:Cardiac Volume / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism; D002950:Citrate (si)-Synthase / Q000378:metabolism; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D019344:Lactic Acid / Q000378:metabolism*; D007811:Lanthanum / Q000493:pharmacokinetics; D008854:Microscopy, Electron; D027501:Monocarboxylic Acid Transporters; D009043:Motor Activity; D018482:Muscle, Skeletal / Q000378:metabolism*; D009210:Myofibrils / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D009929:Organ Size; D051381:Rats; D017207:Rats, Sprague-Dawley; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D016277:Ventricular Function, Left / Q000502:physiology
chemical_list: D002352:Carrier Proteins; D027501:Monocarboxylic Acid Transporters; D019344:Lactic Acid; D007811:Lanthanum; D002950:Citrate (si)-Synthase; D018995:Myosin Heavy Chains