Exchangeability of tissue potassium in skeletal muscle

¹ Laboratory of Cardiovascular Physiology, National Heart Institute, Bethesda, Maryland

The quantity of "rapidly exchanging" K⁺ in isolated, skeletal muscles of dogs was determined by measuring the back-diffusion of K⁴² during perfusion with blood containing this isotopic tracer. This quantity was not constant, but varied from 18% to 88% of the total tissue K⁺. The rapidly exchanging fraction increased as arterial pressure and blood flow increased, and was greater in preparations with low vascular tone. It is concluded that the rapidly exchanging K⁺ represents all tissue K⁺ in well circulated regions, and the remaining K⁺ (slowly exchangeable) all tissue K⁺ in poorly circulated regions. As arterial pressure increases, or vascular tone decreases, the well circulated regions are increased at the expense of the poorly circulated regions due to opening or widening of minute vessels which were originally closed or narrowed.

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