Potassium Exchanges in Man in Brief Exercise

Severe muscular exercise produces a rise in plasma potassium (Ewig and Wiener, 1 Baetjer, 2 Keys 3 ). A loss of potassium from the muscle associated with muscular activities can be proved under some conditions (Fenn 4 ). Does it follow that muscular contraction always involves a loss of potassium from the muscle to the blood stream? Extreme or unphysiological conditions are required to give a positive answer from tissue analyses. Blood sampling studies have not ruled out the red cells as a source of potassium in the immediate changes resulting from brief exercise in man. Calculations from whole blood and plasma are inadequate because of analytical limitations.

Major changes of plasma [K] occur within the exercised region in man at a time when products of metabolism like lactate are only beginning to enter the plasma. Table I gives results from a typical experiment.

We have attempted to evaluate the role of the red cells in the K exchanges in young men exercised by violent running in place for 40 to 60 seconds. Blood samples were drawn under oil from an antecubital vein before and within a few seconds of the end of exercise. The heparinized samples were immediately centrifuged in long centrifuge tubes under oil at 2 to 5°C. After 50 minutes at 2800 r.p.m. the oil was removed and the middle portion of the plasma taken tor analysis. The remaining plasma and the top 0.5 cm of cells were removed and then the cells were sampled by syringe-pipettes (Krogh and Keys 5 ). Plasma and cells were analyzed separately for water (drying at 105°C), total base (Keys 6 ) and potassium (Hartzler 7 ). Duplicates were run on all except K which was analyzed in triplicate.