Ammonium chloride ingestion increases resting mRNA content, but blunts exercise-induced mRNA levels in human skeletal muscle

D.J. Bishop,¹ J. Edge,^2,3 T. Mundel,³ H. Pilegaard,⁴ E. Hawke,⁵ N. Lopez-Villalobos⁶ and R. da Silva Fermino de Oliveira,¹ ¹Institute of Sport, Exercise and Active Living (ISEAL), Victoria University, Melbourne, VIC 8001, Australia, ²Department of Sport and Exercise Science, University of Auckland, New Zealand., ³Institute of Food, Nutrition and Human Health, Massey University, New Zealand., ⁴Centre of Inflammation and Metabolism (CIM), Department of Molecular Biology, University of Copenhagen, Denmark., ⁵Sports and Health Sciences, Dala Sports Academy Dalarna University, Falun, Sweden. and ⁶Institute of Veterinary, Animal and Biomedical Sciences, Massey University, New Zealand.

We have previously observed that minimising the decrease in muscle pH that occurs during high-intensity exercise promotes greater aerobic adaptations (Edge et al., 2006). We subsequently reported that rats ingesting sodium bicarbonate (NaHCO₃) before training sessions (which reduced the activity-induced decrease in muscle pH) had significantly greater adaptations to exercise training (Thomas et al., 2007). This included greater mitochondrial respiration (Bishop et al., 2010) compared to both a control group (no training) and a placebo group (identical training, but ingesting NaClbefore each session). The aim of the present study was to test the hypothesis that intracellular pH may affect some of the cellular signalling pathways and genes that regulate mitochondrial biogenesis - which have previously been demonstrated to be up-regulated by physical activity (Little et al., 2011). Eight active males (Mean±SD, age, 25±6, Body mass 84±9, $\overset{\cdot}{V}$ O_2peak 48±8) performed 10×2 min cycle intervals at 80% $\overset{\cdot}{V}$ O_2peak intensity on two occasions separated by ∼2 weeks. Participants ingested either ammonium chloride (ACID) or calcium carbonate (PLA) the day before and on the day of the exercise trial in a randomised, counterbalanced order, using a crossover design. Biopsies were taken from the vastus lateralis muscle before and immediately after exercise as well as after 2 h of recovery. The mRNA levels of peroxisome proliferator-activated receptor coactivator 1α (PGC-1α), citrate synthase, cytochome c and FOXO1 were elevated at rest following ACID (p < 0.05). During the PLA condition, the mRNA content of mitochondrial- and glucose-regulating proteins was elevated following exercise (p < 0.05). In the early phase (0 – 2 h) of post-exercise recovery during ACID, PGC-1α, citrate synthase, cytochome C, FOXO1, GLUT4, and HKII mRNA levels were not different from resting levels (all p > 0.05), but the difference in PGC-1α mRNA 2 h post-exercise between ACID and PLA approached significance (p = 0.08). The present data show that in resting conditions, short-term metabolic acidosis increases the PGC-1α mRNA level and some of its downstream targets, to levels similar to that found in PLA post-exercise. However, metabolic acidosis abolished the early post-exercise increase of PGC-1α mRNA and the mRNA of downstream mitochondrial and glucose regulating proteins. These findings indicate that metabolic acidosis may affect mitochondrial biogenesis, with divergent effects in resting and exercised muscle.

Bishop DJ, Thomas C, Moore-Morris T, Tonkonogi M, Sahlin K & Mercier J. (2010) American Journal of Physiology Endocrinology and Metabolism 299, E225-33.

Edge J, Bishop D & Goodman C. (2006) Journal of Applied Physiology 101, 918-25.

Little JP, Safdar A, Bishop D, Tarnopolsky MA & Gibala MJ. (2011) American Journal of Physiology -Regulatory Integrative and Comparative Physiology 300, R1303-10.

Thomas C, Bishop D, Moore-Morris T & Mercier J. (2007) American Journal of Physiology -Endocrinology and Metabolism, 293,E916-22.