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Journal of Applied Physiology, Vol 78, Issue 2 513-523, Copyright © 1995 by American Physiological Society
ARTICLES |
L. Gullestad, J. Hallen and O. M. Sejersted
Department of Physiology, National Institute of Occupational Health, Oslo, Norway.
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.
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