Genetic alterations in potassium transport in L cells

Starting with mutagenized cultures of the mouse fibroblastic cell line LM(TK-), we have selected mutant clones by their ability to grow at 0.2 micrometer K+, a concentration unable to support the growth of the parent cell. The mutants fall into two classes on the basis of their potassium transport properties. Both classes maintain a high intracellular K+ concentration when growing in low-potassium medium, and both are unaltered in the ouabain-sensitive Na/K pump. One class shows an increased activity of a ouabain-resistant, furosemide-sensitive K+ transport system; the other class shows a decreased activity of a specific component of K+ efflux.