LACTATE DEHYDROGENASE EXPRESSION AT THE ONSET OF ALTERED LOADING IN THE RAT SOLEUS MUSCLE

Abstract

Both functional overload and disuse atrophy induce a phenotype shift in the primarily slow phenotype rat soleus toward a fast phenotype. Lactate Dehydrogenase (LDH) is an important regulatory enzyme involved in anaerobic glycolysis and catalyzes the interconversion of lactate to pyruvate. The mechanisms inducing differential LDH expression at the onset of increased or decreased loading is not well understood. PURPOSE The purpose of this study was to determine LDH A&B mRNA and protein concentrations at early time points of altered loading in the rat soleus muscle. METHODS Male Sprague-Dawley rat soleus muscle was functionally overloaded for 3 days by synergist ablation or subjected to disuse atrophy by hindlimb suspension for 3 days. LDH mRNA concentration was determined by northern blotting, and LDH isoenzyme composition was determined by zymogram analysis. RESULTS LDH-A mRNA abundance increased 69% (.4±1 vs. 1.3±3, p < 0.05) and LDH-B mRNA abundance decreased 31% (4.82±.56 vs. 3.3±45, p < 0.05) after 3 days of functional overload when compared to control rats. LDH protein expression demonstrated a shift from the slower LDH isoforms to the faster LDH isoforms. There were no changes observed in either LDH-A (2.16±29 vs. 2.27±.19) or LDH-B (1.97±34 vs. 2.08±.21) mRNA abundance following 3 days of hindlimb suspension. CONCLUSIONS In summary, loading induces differential expression of LDH A&B in the rat soleus muscle, which is related to whether loading activity is increased or decreased. Supported by a grant from the South Carolina Space Grant Consortium and ACSM/NASA.