K+ shifts of skeletal muscle during stepwise bicycle exercise with and without beta-adrenoceptor blockade.
1. K+ efflux rate and control of K+ reuptake rate in exercising muscle cells was examined in six healthy female volunteers. 2. A K(+)-selective electrode in the femoral vein continuously monitored K+ concentration ([K+]fv) during bicycling. Power was increased stepwise 5-6 times by 30-40 W every fourth minute until exhaustion before and after I.V. administration of propranolol. Leg blood flow was measured by bolus injections of Cardiogreen. 3. [K+]fv increased from about 4.3 to 6.8 mmol l-1 at exhaustion both before and after propranolol administration, but after drug infusion endurance was reduced from 22.2 +/- 0.6 to 19.7 +/- 1.1 min, so [K+]fv rose more rapidly. 4. The exercise-induced efflux rate of K+ from the muscle cells was estimated to be about 11 mumol kg-1s-1 at exhaustion both before and after propranolol administration. 5. As an indicator of rate of net loss of K+ from the leg, veno-arterial concentration differences ([K+]fv-a) during first, fourth and fifth power increments were high after 15 and 40 s, but declined toward the end of each power step. Propranolol accentuated [K+]fv-a only after 15 and 40 s of the first and fourth increments. 6. The exercise-induced increase in reuptake rate of K+ in the muscle, estimated at exhaustion, was not significantly changed by propranolol and was about 10 mumol kg-1s-1, corresponding to about 15% of maximum Na(+)-K+ pump capacity in man. 7. Extracellular accumulation and loss of K+ from muscle during bicycle exercise is due to Na(+)-K+ pump lag. The higher [K+]fv during propranolol is mainly due to impaired redistribution outside the exercising muscles. In addition at low powers, beta-adrenoceptor blockade caused a transiently increased net loss due to an accentuated Na(+)-K+ pump lag.
Hallén
J
J
Department of Physiology, National Institute of Occupational Health, Oslo, Norway.
Gullestad
L
L
Sejersted
O M
OM
D000328:Adult; D001783:Blood Flow Velocity; D001784:Blood Gas Analysis; D015444:Exercise / Q000502:physiology*; D005080:Exercise Test; D005260:Female; D005268:Femoral Vein; D006400:Hematocrit; D006728:Hormones / Q000097:blood; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007275:Injections, Intravenous; D007773:Lactates / Q000097:blood; D019344:Lactic Acid; D009132:Muscles / Q000187:drug effects / Q000378:metabolism*; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D011433:Propranolol / Q000494:pharmacology*; D011943:Receptors, Adrenergic, beta / Q000187:drug effects* / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
D006728:Hormones; D007773:Lactates; D011943:Receptors, Adrenergic, beta; D019344:Lactic Acid; D011433:Propranolol; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium