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

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.