title: Lactate dehydrogenase expression at the onset of altered loading in rat soleus muscle.
abstract: Both functional overload and hindlimb disuse induce significant energy-dependent remodeling of skeletal muscle. Lactate dehydrogenase (LDH), an important enzyme involved in anaerobic glycolysis, catalyzes the interconversion of lactate and pyruvate critical for meeting rapid high-energy demands. The purpose of this study was to determine rat soleus LDH-A and -B isoform expression, mRNA abundance, and enzymatic activity at the onset of increased or decreased loading in the rat soleus muscle. The soleus muscles from male Sprague-Dawley rats were functionally overloaded for up to 3 days by a modified synergist ablation or subjected to disuse by hindlimb suspension for 3 days. LDH mRNA concentration was determined by Northern blotting, LDH protein isoenzyme composition was determined by zymogram analysis, and LDH enzymatic activity was determined spectrophotometrically. LDH-A mRNA abundance increased by 372%, and LDH-B mRNA abundance decreased by 43 and 31% after 24 h and 3 days of functional overload, respectively, compared with that in control rats. LDH protein expression demonstrated a shift by decreasing LDH-B isoforms and increasing LDH-A isoforms. LDH-B activity decreased 80% after 3 days of functional overload. Additionally, LDH-A activity increased by 234% following 3 days of hindlimb suspension. However, neither LDH-A or LDH-B mRNA abundance was affected following 3 days of hindlimb suspension. In summary, the onset of altered loading induced a differential expression of LDH-A and -B in the rat soleus muscle, favoring rapid energy production. Long-term altered loading is associated with myofiber conversion; however, the rapid changes in LDH at the onset of altered loading may be involved in other physiological processes.
authors.affiliation: Integrative Muscle Biology Laboratory, Exercise Science Department, Norman J. Arnold School of Public Health, University of South Carolina 29208, USA.
authors.forename: Tyrone A
authors.initials: TA
authors.lastname: Washington
authors.forename: James M
authors.initials: JM
authors.lastname: Reecy
authors.forename: Raymond W
authors.initials: RW
authors.lastname: Thompson
authors.forename: Larry L
authors.initials: LL
authors.lastname: Lowe
authors.forename: Joseph M
authors.initials: JM
authors.lastname: McClung
authors.forename: James A
authors.initials: JA
authors.lastname: Carson
mesh_terms: D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D012090:Cumulative Trauma Disorders / Q000503:physiopathology*; D019417:Hindlimb Suspension / Q000009:adverse effects* / Q000379:methods*; D007770:L-Lactate Dehydrogenase / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000503:physiopathology*; D009133:Muscular Atrophy / Q000209:etiology* / Q000503:physiopathology*; D005082:Physical Exertion; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D007770:L-Lactate Dehydrogenase