Acid-base and ion regulation during exercise with emphasis on horses
2005
Vengust, M., Ljubljana Univ. (Slovenia). Veterinary Fac.
Exercise induced intracellular and extracellular acidosis requires a number of homeostatic adaptations to return acid base status to its resting level. The purpose of this review is to briefly describe the quantitative approach to these homeostatic adaptations, and to describe intracellular (intramuscular and intraerythrocyte) and extracellular (plasma) ion kinetics during exercise. Special consideration is given to horses. Ions and carbon dioxide (CO2) movement between muscle and plasma and output of CO2 by the respiratory system play a critical role in acid base homeostasis. The skeletal muscle acidosis is largely driven by a fall in intramuscular strong ion difference due to increase in intramuscular lactate concentration (La-) and reduction in intramuscular potassium concentration (K+). The increase in intramuscular hydrogen ion concentration is buffered by a reduction in creatine phosphate concentration (CrP2-), and by a small change in the apparent equilibrium constant (KA) for weak acid buffers. Diffusion of La- into venous blood and its associated metabolism, re-uptake of K+, and diffusion of CO2 from muscle and its pulmonary elimination contribute to the resolution of acidosis. CrP2- is resynthesized, and KA reverts to its resting value.
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