Muscular origin of elevated plasma potassium during exercise.

Abstract

In healthy subjects plasma potassium (K) concentrations increased from resting levels of 3. 8 mEq/liter to 5 mEq/liter during treadmill walking with average O2 consumptions of 2 liters/min. Whole blood K levels increased similarly as arterial blood hydrogen (H) ion concentration increased 5. 9 nmoles/liter and bicarbonate levels decreased 1. 6 mEq/liter. Similar changes occurred in ambulatory patients walking to produce O2 consumptions of 1, 200 ml/min. Plasma draining from the exercising forearms of similar subjects contained 0. 7 mEq/ liter more K than did arterial plasma. Whole blood K concentration CO2 tension, H ion and bicarbonate levels were elevated in such venous blood but arterial blood levels were unchanged. It is postulated that exercise produced acidois in muscle cells, that some K was exchanged for H ions, and both were released from striated muscle. This is most consistent with the increased H ion concentration of arterial blood during moderate systemic exercise and in blood draining from the exercising forearm. However, in view of the small fraction of change in muscle K required to produce a large increase in extracellular K, other mechanisms may explain the liberation of K into venous blood during exercise.