Extracellular K+ concentration and K+ Balance of the gastrocnemius muscle of the dog during exercise

Abstract

Exercise-induced changes of the extracellular and the venous K⁺ concentrations ([K⁺]_e, [K⁺]_ven) were measured continuously in autoperfused dog gastrocnemii using PVC liquid membrane electrodes. O₂ consumption (\(\dot V\)O₂), blood flow and performance of the muscles were also determined. The muscles were stimulated indirectly and isotonic tetanic contractions (0.2 s) were produced every 0.7 s for more than 45 min. 1. [K⁺]_e started to increase immediately after the onset of exercise and reached a maximal value of 7.4 meq/l after 4 min of exercise, thereafter it decreased, reaching 5.3 meq/l at the end of the 12 min exercise. After 6 min of recovery [K⁺]_e became lower than the control level. [K⁺]_ven reached maximal values of 5.0 meq/l after 30 s of exercise and thereafter decreased slowly to 3.8 meq/l at the end of exercise. Thus, a K⁺ gradient of up to 3 meq/l was observed between the interstitial space and the venous blood. About 30 s after the end of exercise a net K⁺ uptake of up to 0.3 μeq per min per g was observed. 2. The K⁺ loss of the muscle fibres reached maximal values of 1.5 μeq per min per g at 1.5 min after the onset of exercise. Total K⁺ loss was 7% during 12 min of exercise and 12.5% of intracellular K⁺ during 45 min of exercise. 3. The changes of [K⁺]_e correlated closely with performance and\(\dot V\)O₂ during exercise but not during recovery. On the other hand, blood flow correlated with the changes of [K⁺]_e during both exercise and recovery. These results support the hypothesis that changes of [K⁺]_e of the working muscle might be an important factor regulating exercise hyperemia.