Unidirectional K+ fluxes in rat thymocytes stimulated by concanavalin A

Abstract

Unidirectional K⁺ fluxes were estimated in isolated rat thymocytes by ⁴²K exchange kinetics. The cells were either preloaded with isotope and the release of it measured during incubation for one hour at 38°C, or the cellular uptake of isotope during a similar incubation was measured.The influx rate of untreated thymocytes was: 2.3·10⁻¹² moles cm ^−2. S⁻¹ and efflux rate: 1.8·10⁻¹² moles cm ^−2· S⁻¹·When con A was added to the cells, influx was raised 74% and efflux 65%. Maximal effect was obtained when the concentration of con A was 15 μg/ml, but concentrations as low as 0.75 μg/ml were effective.Hydrocortisone resistant thymocytes responded at least as well as untreated cells to con A, which also raised RNA synthesis rate in the former cells 2.5 times.Using an extracellular marker, ⁵¹CrEDTA, intracellular concentrations of some ions was estimated in the thymocytes after one hour incubation: Na⁺: 30 mmoles/kg water, K⁺: 177 mmoles/kg water and Cl⁻: 43 mmoles/kg water. Cellular water content: 69%. These values were not found significantly altered when con A was present.Since con A raised influx and efflux to the same extent and no net flux of K⁺ could be detected, it is proposed that both active and passive transport of K⁺ was increased by con A.The increased fluxes induced by con A, can apparently not be reversed by removal of con A from the incubation medium or by addition of the inhibiting hapten, α‐methyl‐D‐mannoside.