Sodium bicarbonate ingestion prior to training improves 1 mitochondrial adaptations in rats

27 We tested the hypothesis that reducing hydrogen ion accumulation during training 28 would result in greater improvements in muscle oxidative capacity and time to 29 exhaustion (TTE). Male Wistar rats were randomly assigned to one of three groups 30 (CON, PLA, BIC). CON served as a sedentary control, while PLA ingested water and 31 BIC ingested sodium bicarbonate 30 min prior to every training session. Training 32 consisted of 7 12, 2-min intervals performed 5x/wk for 5 wk. Following training, TTE 33 was significantly greater in BIC (81.2 ± 24.7 min) compared to PLA (53.5 ± 30.4 min), 34 and TTE for both groups was greater than CON (6.5 ± 2.5 min). Fibre respiration was 35 determined in the soleus (SOL) and extensor digitorum longus (EDL), with either 36 pyruvate (Pyr) or palmitoyl-carnitine (PC) as substrates. Compared to CON (14.3 ± 2.6 37 nmol O2/min/mg d.w.), there was a significantly greater SOL-Pyr state-3 respiration in 38 both PLA (19.6 ± 3.0 nmol O2/min/mg d.w.) and BIC (24.4 ± 2.8 nmol O2/min/mg 39 d.w.), with a significantly greater value in BIC. However, state-3 respiration was 40 significantly lower in the EDL from both trained groups, compared to CON. These 41 differences remained significant in the SOL, but not the EDL, when respiration was 42 corrected for citrate synthase activity (an indicator of mitochondrial mass). These novel 43 findings suggest that reducing muscle hydrogen ion accumulation during running 44 training is associated with greater improvements in both mitochondrial mass and 45 mitochondrial respiration in the soleus. 46 47 Key-words: mitochondrial respiration, state-3 respiration, muscle pH, citrate synthase, 48 muscle buffer capacity 49