SULFATE CONCENTRATIONS AND TRANSPORT IN HUMAN BRONCHIAL EPITHELIAL-CELLS

Inorganic sulfate concentrations in the cytoplasm of human bronchial e pithelial cells exceeded levels in the bathing medium under all circum stances tested. Cell sulfate concentrations were directly related to m edium sulfate concentrations and inversely related to medium chloride concentrations. In physiological media there was a sulfate compartment of approximately 0.3 mM that exchanged very slowly with extracellular sulfate. In media lacking chloride, sulfate was accumulated by the ce lls to a level as high as 2 mM. Sulfate uptake was markedly inhibited by external chloride and by stilbene sulfonic acid derivatives but was not affected by sodium in the medium. Efflux of (SO42-)-S-35 was stim ulated by both chloride and sulfate in the bathing medium but inhibite d by stilbenes. The following compounds had no effect on sulfate movem ents: phorbol esters, adenosine 3',5'-cyclic monophospate derivatives, and okadaic acid. Changes in medium tonicity were likewise without ef fect. Our results suggest that human bronchial epithelial cells mainta in a steady-state disequilibrium for inorganic sulfate. Furthermore, s ulfate appears to exist in at least two compartments in the cells: one that is slowly exchangeable with sulfate in the medium and another ex changeable compartment that is of negligible size in physiological med ia but that becomes very large in media lacking chloride. Sulfate is t ransported by an anion exchanger of broad specificity that is not infl uenced by substances known to modulate chloride channels.