Cat Heart Muscle in Vitro : VI. Potassium exchange in papillary muscles

The exchange of cell K with K⁴², J_K, has been measured in cat right ventricular papillary muscle under conditions of a steady state with respect to intracellular K concentration. Within the limits of the measurement, all of cell K exchanged at a single rate. Cells from small cats are smaller and have larger surface/volume ratios than cells from large cats. The larger surface/volume ratio results in larger flux values. J_K increases in an approximately linear manner as the external K concentration is increased twentyfold, from 2.5 to 50 mM, at constant intracellular K concentration. The permeability for K ions, P_K, calculated from the influx and membrane potential, remains very nearly constant over this range of external K concentrations. J_K is not affected by replacement of O₂ by N₂, or by stimulated contractions at 60 per minute, but K influx decreases markedly in 10^-5 M and 10^-8 M ouabain.