Serum stimulation of potassium fluxes, ouabain binding, and sodium fluxes in quiescent chicken embryo fibroblasts

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Abstract
Growth‐contingent alterations in potassium and sodium fluxes, ouabain binding, and potassium ion content were examined following serum stimulation of quiescent, density‐inhibited chicken embryo fibroblasts. Serum stimulation resulted in very rapid 1.5‐ to 1.8‐fold increases in ouabain‐sensitive potassium influx and lesser 1.4‐ to 1.5‐fold increases in potassium efflux and sodium influx. Potassium influx stimulation was maximal after addition of 5–20% calf serum and was unaffected by cycloheximide inhibition of protein synthesis. Reflecting the slightly greater stimulation of potassium influx versus potassium efflux, potassium ion levels were 10–15% higher in serum‐stimulated compared to unstimulated cells. Specific ouabain binding levels in stimulated and unstimulated control cells were initially similar, however, by four hours after stimulation a 40–50% increase in specific ouabain binding was observed. Incubation with ouabain was found also to inhibit later serum‐stimulated hexose uptake and thymidine incorporation; this blockage may be a consequence of subnormal potassium levels rather than ouabain inhibition of the serum‐stimulated potassium influx.

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