Location of fractions of potassium in rabbit auricles

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Abstract
Sarcosomes and microsomes have been isolated from rabbit auricles by dispersion of the tissue in sucrose (0⋅28 M)-ethylene diaminetetra-acetate (0⋅01 M) and high-speed centrifugation at 0 to 1 °C. Of the total tissue potassium, about 10% was recovered from the 700 g -min fraction, which contained nuclei and coarse cell debris: 2 % from the 45000 or 250000 g -min fraction, which contained mainly sarcosomes and 0⋅7 % from the 750000 g -min fraction which contained mainly microsomes. When the auricles were immersed in physiological saline solution containing 42 K for 15 or 120 min before separation, the specific activity of the fractions differed, being highest in the particle-free suspending medium, intermediate in the sarcosomes and near to zero in the microsomes. The specific activity of the particle free fraction agreed closely and that of the sarcosomes moderately well with values predicted by analysis of the exchange in intact auricles. Dinitrophenol (10 -4 M) arrested uptake of 42 K by sarcosomes. Ouabain (10 -5 M) had no direct effect on the exchange. From measurements of electron micrographs it appeared that the sarcosomes occupied 8⋅2 ± 0⋅3 (S. E.) % of the intracellular volume. It is likely that the sarcosomes lost much of their potassium during extraction and probably contain most of the 21 % of the tissue potassium which exchanges slowly in the intact isolated tissue.