Erythrocyte ion regulation across inactive muscle during leg exercise.

Ion concentration changes in whole blood, plasma, and erythrocytes across inactive muscle were examined in eight healthy males performing four 30-s bouts of maximal isokinetic cycling with 4 min rest between each bout. Blood was sampled from the arm brachial artery and deep antecubital vein during the intermittent exercise period and for 90 min of recovery. Arterial and venous erythrocyte lactate concentration ([Lac-]) increased from 0.3 +/- 0.1 to 12.5 +/- 1.3 (p < 0.01) and 1.1 +/- 0.4 to 8.5 +/- 1.5 mmol/L (p < 0.01), respectively, returning to control values during recovery. Arterial and venous plasma [Lac-] increased from 1.5 +/- 0.2 to 27.7 +/- 1.8 and from 1.3 +/- 0.4 to 25.7 +/- 3.5 mmol/L, respectively, and was greater than erythrocyte [Lac-] throughout exercise and recovery. Arterial and venous [K+] increased in erythrocytes from 119.5 +/- 5.1 to 125.4 +/- 4.6 (p < 0.01) and from 113.6 +/- 1.7 to 120.6 +/- 7.1 mmol/L, respectively, decreasing to control during recovery. In arterial and venous plasma, [K+] increased from 4.3 +/- 0.1 to 6.1 +/- 0.2 (p < 0.01) and from 4.5 +/- 0.2 to 5.3 +/- 0.2 mmol/L (p < 0.01), respectively, decreasing to control during recovery. The efflux of Lac- out of erythrocytes against an electrochemical concentration gradient suggests the presence of an active transport system. Efflux of K+ from erythrocytes as blood passes across inactive muscle affords an important adaptation to the K+ release from muscle activated in heavy exercise.