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 () was increased during exercise after glycogen depletion, in spite of a marked increase in plasma pH (pH_P). It was further demonstrated that 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, 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, 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 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 but apparently did not overcompensate for a possible decrease in due to increased pH_P. The close relationship between 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.