Exchangeability of tissue potassium in skeletal muscle.

RENKIN, EUGENE M. Exchangeability of tissue potassium in skeletal muscle. Am. J. Physiol. 1g7(6): I~II-12 15. I g5g.-The quantity of ‘rapidly exchanging’ Kf 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 da/$ to 88y0 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 Kf represents all tissue K+ in well circulated regions, and the remaining Kf (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.