title: Potassium fluxes in contracting human skeletal muscle and red blood cells.
abstract: The present study examined K+ fluxes in red blood cells and muscle during muscle contractions. Seven subjects performed two-legged submaximal knee-extensor exercise for 30 min. After 10 min of leg exercise (L1), intense arm exercise was also performed for 10 min (L2+A). Plasma epinephrine and norepinephrine concentrations were higher (P < 0.05) in L2+A compared with L1. Arterial plasma K+ at the end of L2+A was higher than in L1 (5.6 vs. 4.4 mM, P < 0.05) and returned to the L1 level on cessation of arm exercise. A net K+ release of 0.16 mmol/min from the active legs during L1 was turned to a net K+ uptake of 0.79 mmol/min during L2+A. Both arterial and venous red blood cell K+-to-hemoglobin ratios were constant during exercise. The present data suggest that contracting muscle can take up K+ probably by a combination of K+ and hormone activation of the Na+-K+ pump. Furthermore, changes in red blood cell K+ concentrations during muscle activity appear to be due to water movements and not transmembrane fluxes of K+.
authors.affiliation: Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, DK-2100 Copenhagen, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Juel
authors.forename: Y
authors.initials: Y
authors.lastname: Hellsten
authors.forename: B
authors.initials: B
authors.lastname: Saltin
authors.forename: J
authors.initials: J
authors.lastname: Bangsbo
mesh_terms: D000328:Adult; D002395:Catecholamines / Q000097:blood; D004911:Erythrocyte Volume / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000097:blood; D007866:Leg / Q000098:blood supply; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D012039:Regional Blood Flow / Q000502:physiology
chemical_list: D002395:Catecholamines; D019344:Lactic Acid; D011188:Potassium