Importance of pH regulation and lactate/H plus transport capacity for work production during supramaximal exercise in humans

We examine the influence of the cytosolic and membrane-bound contents of carbonic anhydrase (CA; CAII, CAIII, CAIV, and CAXIV) and the muscle content of proteins involved in lactate and proton transport [monocarboxylate transporter (MCT) 1, MCT4, and Na+/H+ exchanger 1 (NHE1)] on work capacity during supramaximal exercise. Eight healthy, sedentary subjects performed exercises at 120% of the work rate corresponding to maximal oxygen uptake (W-max) until exhaustion in placebo (Con) and metabolic alkalosis (Alk) conditions. The total (W-tot) and supramaximal work performed (W-sup) as measured. Muscle biopsies were obtained before and immediately after standardized exercises (se) at 120% W-max both conditions to determine the content of the targeted proteins, the decrease in muscle pH (Delta pH(m)), and the muscle lactate accumulation ([Lac](m)) per joule of W-sup (Delta pHm/Wsup-se and Delta[Lac](m)/Wsup-se, respectively) and the dynamic buffer capacity. In Con, W-sup was negatively correlated with Delta pH(m)/Wsup-se, positively correlated with Delta[Lac] (m)/Wsup-se and MCT1, and tended to be positively correlated with MCT4 and NHE1. CAII + CAIII were correlated positively with Delta pH(m)/Wsup-se and negatively with Delta[Lac](m)/Wsup-se, while CAIV was positively related to W-tot. The changes in W-sup with Alk were correlated positively with those in dynamic buffer capacity and negatively with W-sup in Con. Performance improvement with Alk was greater in subjects having a low content of proteins involved in pH regulation and lactate/proton transport. These results show the importance of pH regulating mechanisms and lactate/proton transport on work capacity and the role of the CA to delay decrease in pH(m) and accumulation in [Lac](m) during supramaximal exercise in humans.