Plasma potassium and ventilation during incremental exercise in humans: modulation by sodium bicarbonate and substrate availability

Summary

It has recently been demonstrated that, compared to normal conditions, ventilation ($\dot V_E$) was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pH_P). It was further demonstrated that$\dot V_E$ in patients with McArdle's syndrome was reduced when substrate availability was improved. In the present experiments, six endurance trained men performed two successive cyclo-ergometric incremental exercise tests (tests A, B) after normal nutrition (N) and after a fatty meal in conjunction with a sodium bicarbonate (NaHCO₃) solution (F_SB) or without NaHCO₃ (F), and the relationship between$\dot V_E$, plasma potassium concentration ([K⁺]P), and pHP was checked. Plasma free fatty acid concentration ([FFA]_P) was markedly increased in the F and FSB trials (P<0.001). In F_SB pH_P was significantly increased, compared to N and F (P<0.001). In all the B tests, pH_P increased during moderate and intense exercise and in F_SB, remained alkalotic even during maximal exercise intensity. In contrast,$\dot V_E$ and [K⁺]_P changes were almost equal in all the trials and in tests A and B. It was found that exercise-induced changes of$\dot V_E$ and [K⁺]_P in the present experiments were not markedly affected by [FFA]_P or pH_P values and that these changes also occurred independently of changes in pHP or plasma bicarbonate concentration. The often used glycogen depletion strategy may have slightly increased$\dot V_E$ but apparently did not overcompensate for a possible decrease in$\dot V_E$ due to increased pH_P. The close relationship between$\dot V_E$ and [K⁺]_P was not affected by acid-base or substrate changes; this would further confirm the hypothesis that K⁺ may act as a stimulus for exercise$\dot V_E$.