K+ balance of the quadriceps muscle during dynamic exercise with and without beta-adrenoceptor blockade.
The effect of propranolol (0.15 mg/kg body wt) on K+ fluxes was investigated in seven healthy males performing 8-min two-legged knee-extension exercise at two different powers. K+ concentration was measured in the femoral vein by a K(+)-selective electrode, and leg blood flow was measured by the dye-dilution technique. During control bouts, rates of change in femoral venous K+ concentration were 38 +/- 10 and 53 +/- 8 mumol.l-1.s-1 at onset of exercise (K+ efflux) and -14 +/- 3 and -34 +/- 3 mumol.l-1.s-1 at cessation of exercise (K+ reuptake) at low and high powers, respectively. This mismatch between K+ efflux and reuptake rates fits with the steady-state K+ loss rate of 0.14 +/- 0.04 and 0.32 +/- 0.09 mmol/min. Propranolol raised K+ efflux rate, did not modify K+ reuptake rate or steady-state K+ loss, but caused transiently increased K+ loss rate at the onset of exercise, thus accentuating the rise of arterial K+ concentration. In conclusion, the continuous muscle K+ loss during steady-state exercise with a small muscle mass is not due to lack of catecholamine stimulation, but beta-adrenoceptor blockade increased the Na(+)-K+ pump lag so that the initial K+ loss at onset of exercise was increased.
Gullestad
L
L
Department of Physiology, National Institute of Occupational Health, Oslo, Norway.
Hallén
J
J
Sejersted
O M
OM
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D001794:Blood Pressure / Q000187:drug effects / Q000502:physiology; D002395:Catecholamines / Q000097:blood; D015444:Exercise / Q000502:physiology*; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D017736:Ion-Selective Electrodes; D007866:Leg / Q000098:blood supply; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D010042:Ouabain / Q000378:metabolism; D010101:Oxygen Consumption / Q000187:drug effects; D011188:Potassium / Q000378:metabolism*; D012039:Regional Blood Flow / Q000187:drug effects / Q000502:physiology; D000254:Sodium-Potassium-Exchanging ATPase / Q000187:drug effects
D000319:Adrenergic beta-Antagonists; D002395:Catecholamines; D006454:Hemoglobins; C028996:cardiac glycoside receptors; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium