The Effect of Cycloserine on Metabolism and Contractile Function in Rodent Skeletal Muscle

Abstract

<p> We hypothesized that acute inhibition of the contraction-induced expansion of the muscle TCA cycle intermediate (TCAI) pool via would not adversely effect metabolism or contractile function. Forty rats were anaesthetized and the gastrocnemius muscle (GAS) from one leg was vascularly isolated and perfused with saline (CON) or a red cell media containing DL-cycloserine (CYCLO; Sigma C-7005; dose=0.05 mg/g), an inhibitor of alanine aminotransferase (AAT). After 1h of perfusion, the GAS muscle was either snap frozen (CON-Rest, n=11; CYCLO-Rest, n=9) or stimulated to contract for 10 min (1Hz, 0.3 ms, 2 V) with blood flow fixed at 30 ml min-1 100g-1 and then snap frozen (CON-Stim, n=10; CYCLO-Stim, n=10). The maximal activity of AAT was lower (P≤0.05) at both CYCLO-Rest (0.61±0.02 mmol·kg-1w.w./min; mean± SEM) and CYCLO-Stim (0.63±0.01 mmol·kg-1w.w./min) vs CON-Rest (3.56±0.16 mmol·kg-1w.w./min) and CON-Stim (3.92±0.29 mmol·kg-1w.w./min). Consistent with lower net flux through AAT, muscle [alanine] was lower (P≤0.05) after CYCLO-Stim (6.97±0.26 mmol·kg-1 dw) compared to CON-Stim (8.55±0.56 mmol·kg-1 dw) and not different vs CON-Rest (6.79±0.41 mmol·kg-1 dw). The sum of five measured TCAI (malate, fumarate, citrate, isocitrate, and 2-oxoglutarate) was higher (P≤0.05) at both CON-Rest (2.10± 0.09 mmol·kg-1 dw) and CON-Stim (2.48± 0.11 mmol·kg-1 dw) vs CYCLO-Rest (1.56± 0.11 mmol·kg-1 dw) and CYCLO-Stim (1.88± 0.15 mmol·kg-1 dw) respectively. Despite the reduction in [TCAI] following CYCLO treatment, there was no difference between conditions in muscle lactate accumulation or phosphocreatine degradation after 10 min of stimulation. Contractile function was not different (P≤0.05) between conditions at either rest or stimulation and the decline in force production over ten minutes of stimulation was identical (~60%) between CON-Stim and CYCLO-Stim respectively. We conclude that flux through AAT was reduced after cycloserine treatment, however the acute inhibition of TCAI expansion did not compromise aerobic energy provision. These data support the hypothesis that the contraction-induced increase in muscle [TCAI] is not causally linked to oxidative energy delivery.</p>