Effect of serum on sodium pump activity at various concentrations of internal and external sodium in mouse (3T3) and human (HeLa) cells.
Serum causes a large rise in the ouabain-sensitive K influx in 3T3 and other cells. It has been argued that this is secondary to the increased Na and K leaks which are also caused by serum. We have measured the K influx into 3T3 and HeLa cells at various values of intracellular Na concentration ([Na]i), and from Na-free medium in 1 and 20% (v/v) serum. Raising [Na]i increases the K influx, but saturation does not occur over the range of [Na]i studied. The estimated Km for [Na]i is around 130 mM and the Vmax some 10 times that of the resting K influx at normal (20 mM) [Na]i. Serum stimulates the K influx by a constant proportion at all values of [Na]i studied, and in Na-free medium. These results are inconsistent with previous explanations of the serum stimulation of pumping.
D000818:Animals; D002478:Cells, Cultured; D003470:Culture Media; D006367:HeLa Cells / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*
D003470:Culture Media; D007473:Ion Channels; D010042:Ouabain; D012964:Sodium; D011188:Potassium