Abstract
Potassium accumulation was studied in slices equilibrated in solutions of varying potassium concentration ([K](ex) = 0-20 mM). Steady-state (42)K uptake was also measured under similar conditions. The accumulated potassium characterized by slow exchange kinetics (half time more than 25 min) exhibited saturation behavior at high external concentrations (maximum, 119 meq/kg dry solid), and exhibited cooperative interaction with sodium. Values calculated from an adsorption isotherm based on solute-protein interaction in a fixed charge system were in agreement with the experimental results. Rubidium competitively inhibited the accumulation of potassium. Studies of the (42)K flux indicated that the rate constants for the slow component decreased with increasing [K](ex). At [K](ex) = 3.33 mM a minimum of about 0.88 x 10(-4) sec(-1) was reached. The potassium flux exhibited saturation behavior at high [K](ex) (maximum 10.5 x 10(-3) meq/kg d.s. per sec). A diffusion coefficient of 1.1 x 10(-5) cm(2) sec(-1) adequately characterized the fast exchanging potassium. A portion of this component exhibited saturation behavior (maximum, 11 meq/kg d.s.) and followed the Langmuir adsorption isotherm. The properties exhibited by potassium accumulation and permeation processes were consistent with those of a fixed charge system as formulated in the "association-induction hypothesis." It is suggested that this model provides an analytical basis for future experimentation.