Characterization of a BALB/c 3T3 preadipose cell mutant with altered Na+K+Cl− contransport activity

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Abstract
A BALB/c 3T3 cell mutant (3T3‐E12) was isolated by its ability to survive at a low extracellular K+ concentration (0.14 mM). The growth rate of mutant cells was less dependent on external K+ than parental cells. Analysis of potassium transport revealed that 3T3‐E12 cells have a decreased activity of the furosemide‐sensitive Na+K+Cl− contrasport system, both in the efflux and influx modes. This is shown to be a result of a decrease in the apparent affinity of the transport system for K+ and Na+, but not Cl−. Upon exposure to the phorbol ester 12‐0‐tetradecanoyl‐phorbol‐13‐acetate (TPA), BALB/c 3T3 cells exhibited a maximal volume decrease of 20%, while mutant cells shrunk by only 7%, suggesting that regulation of cell volume, at least after exposure to a tumor promoter, is impaired in mutant cells compared to parental 3T3 cells.