Introduction: 

Ingestion of an alkaline solution such as sodium bicarbonate (NaHCO₃^-) 1–3 h before exercise results in an increase in plasma HCO₃^- concentration ([HCO₃^-]) and a decrease in plasma hydrogen ion [H⁺] at the start of exercise. An increase of extracellular NaHCO₃^- buffer capacity is a way to facilitate the efflux of H⁺ and lactate (La) from the muscle cell and thereby delay the critical decrease in intracellular pH during high-intensity exercise. In erythrocytes (RBC) La and H⁺ ions are transported (symport) by the monocarboxylate-transporter-1 (MCT-1). La and H⁺ ions equilibrate according to an electrochemical equilibrium (Donnan equilibrium). Ingestions of HCO₃^- may change the RBC membrane potential and/or the transmembrane concentrations of HCO₃^- and ions leading to a different equilibration under resting conditions as well as to different reactions under exercise. Therefore we investigated effects of sodium bicarbonate ingestion on pH and La distribution in RBC and plasma after short term high intensity exercise.

Methods: 

10 healthy male subjects participated in this study. Subjects performed a 15–18sec lasting maximal exercise in judo. Subjects were instructed to perform the test in maximal effort. 2h before exercise subjects ingested HCO₃^- or a placebo. Blood samples were taken pre ingestion, pre exercise, 0min, 1min, ..., 10min after exercise to determine [La] in whole blood, plasma and erythrocytes and blood gas parameters.

Results: 

The [HCO₃^-] and the [H⁺] in plasma were significantly increased/decreased after HCO₃^- ingestion at all time points compared to the placebo ingestion. The mean ratio between RBC and plasma [La] under resting conditions did not differ between both conditions (0.49 0.03 [AU] (Verum) vs. 0.49 0.05 [AU] (Placebo), showing a plasma [La] approximately twice as high as in RBC. The ratio between RBC and plasma [La] significantly decreased (0.34 0.05 [AU] (Verum) vs. 0.33 0.05 [AU] (Placebo)) 0min post exercise, in both situations, showing a faster relative or proportional increase in plasma [La] compared to RBC [La]. No significant differences in the ratio were found for all time points.

Discussion: 

The decrease in ratio is the consequence of a delayed La transport across RBC membrane and the consequence of saturation of the transport systems. The fast congestion of La in plasma exceeds the transport capacity of the RBC membrane. NaHCO₃^- ingestion and therefore the decrease in extracellular [H⁺] had no significant influence on the transportation of lactate across RBC and the muscle membrane. It seems that the decrease in pH caused by exercise was not high enough to influence transportation across the sarcolemma. For RBC a new equilibrium for H⁺, HCO₃^-, and lactate might be adjusted already under resting conditions reflecting no altered gradients and which does not influence lactate transport across RBC membrane.