Proceedings of the National Academy of Sciences of the United States of America
In culture medium deficient in Ca2+, NIH mouse 3T3 cells lose K+, gain Na+, and stop growing. A marked increase in the rate of K+ efflux accounts for this loss; Na+, K+-ATPase pump activity increases but does not fully compensate for enhanced K+ efflux. Phorbol esters and cycloheximide inhibit K+ loss in Ca2+-deficient medium. Phorbol esters inhibit K+ efflux from human fibroblasts as well, even at physiological levels of Ca2+. Two cell lines derived from NIH-3T3, one transformed by a simian virus 40 deletion mutant, the other by the polyoma virus oncogene encoding the middle-sized tumor antigen, retain K+ and can multiply in medium with low Ca2+. Efflux of K+ from these cells is relatively insensitive to reduced Ca2+ concentration, phorbol esters, and cycloheximide. The results suggest the following hypothesis: a channel, nonselective for K+ and Na+, opens when NIH-3T3 cells are in Ca2+-deficient medium; the channel is controlled by the receptor for phorbol ester (protein kinase C) and may also be regulated by a short-lived protein.
Lubin, Martin, "K+ Efflux in NIH Mouse 3T3 Cells and Transformed Derivatives: Dependence on Extracellular Ca2+ and Phorbol Esters." (1988). Open Dartmouth: Faculty Open Access Articles. 1194.