Factors affecting the permeability of isolated fat-cells from the rat to [42K]potassium and [36Cl]chloride ions

Abstract

1. The effluxes of 42K+ and 36Cl− from isolated fat-cells from the rat were studied under a variety of conditions known to affect the metabolism of the cells. 2. 42K+ efflux from isolated fat cells was increased in a Na+-free–high-K+ medium and decreased in a K+-free medium. The existence of K+ exchange diffusion across the fat-cell membrane is suggested. 3. 36Cl− efflux from isolated fat-cells was decreased when the Cl− component of the wash medium was replaced by acetate. The basal 36Cl− efflux is suggested to be partly by Cl− exchange diffusion and partly in company with a univalent cation. 4. A variety of lipolytic stimuli, adrenaline, adrenocorticotrophic hormone, N-6,O-2′-dibutyryladenosine cyclic 3′:5′-monophosphate and theophylline, increased 42K+ efflux from isolated fat-cells. The adrenaline stimulation was biphasic; an initial, rapid and transient increase in 42K+ loss from the fat-cells was followed by a slower, more prolonged, increase in 42K+ efflux. The initial phase was inhibited by phentolamine but not by propranolol. 5. Insulin increased 42K+ efflux only after preincubation with the cells.