Fast and slow fractions of K+ flux in human lymphocytes

Abstract

Potassium influx and efflux were studied in human peripheral blood lymphocytes equilibrated over a wide range of external K⁺ levels. The absence of a net ion movement throughout the flux study was established, trapped space was measured with polyethylene glycol, and cells were separated from incubation media without exposure to any washing solution. There are both rapid and slow cellular fractions of ⁴²K influx and efflux, with half-times of exchange of around 2 minutes, and 400 minutes, respectively. The rapid component is identical in magnitude to the smaller non-saturable component of cell K⁺, while the slow component is identified with the larger, sigmoidal, saturable component of cell K⁺ that was previously shown to follow a cooperative adsorption isotherm. These results support the association-induction hypothesis, which predicts (a) a rapid fraction of K⁺ flux due to equilibration of ion within cell water existing in a state of polarized multilayers, and (b) a slower component of K⁺ flux limited by adsorption onto, or desorption from, fixed anionic sites existing throughout the cell. K⁺ influx, as a function of external K⁺, showed a triphasic relation with a peak around 1 mM K, then a trough around 4 mM K, and then a gradual rise. This relation was readily explained, in terms of the association-induction hypothesis, by the cooperative interaction between, and ion occupancy of, fixed anionic sites that absorb K⁺ or Na⁺.