Effects of external potassium on potassium efflux and accumulation by rat adipocytes

Effects of external K+ concentration, [K+]o, on K+ transport rate and on relative K+, an index of intracellular K+ concentration, were studied in adipocytes isolated from rat epididymal fat pads. 2. Relative K+ changed upon a step change of [K+]o from normal, but with continued exposure to the second [K+]o the relative K+ returned to or approached the initial level. 3. Reversal of the initial change in relative K+ was accelerated by restoration of a normal [K+]o. 4. 42K efflux from cells exposed to a single [K+]o was described by a single rate constant for a wash-out period of up to four half-times. 5. The rate constant was bi-stable with respect to [K+]o, with the critical [K+]o between 3-6 and 4-8 mM. 6. Rate constants were independent of relative K+ and uncorrelated with net fluxes. 7. It is suggested that [K+]o exerts its effects only at the outer surface of the adipocyte membrane.