Increase in K+ and alpha-AIB active transport in CHO cells after low [K+] treatment.

We have studied the effects of prolonged incubation in low [K+] medium (approximately 0.3 mM) on both K+ and amino acid transport in Chinese hamster ovary (CHO) cells. When incubated in low [K+] medium, CHO cells redressed partially the loss of intracellular K+ after 12 h. After 24 h of incubation, both the activity of Na+-K+-ATPase in crude homogenates, and the transport capacity (Vmax) for ouabain-sensitive (i.e., active) K+ influx approximately doubled. The magnitude of the ouabain-insensitive (i.e., passive) K+ influx decreased by 50%. Thus the regulatory response involves an apparent increase in Na+-K+ pump and a decrease in K+ leak. The transport capacity for the nonmetabolized amino acid, alpha-aminoisobutyric acid (alpha-AIB), also increased after 24 h in low [K+] medium. The Vmax for the Na+-dependent (i.e., active) alpha-AIB influx increased by about 150%, and the magnitude of the Na+-independent influx increased by 20-40%. These changes in alpha-AIB transport result in a twofold greater capacity to accumulate this amino acid. Thus the regulation of K+ and alpha-AIB transport systems appears to be linked and possible mechanisms of this linkage are discussed.