| Abstract: | The relation of membrane transport of alkali cations to their external concentrations or to their cellular contents was studied in HeLa cells. Chilling the cells at 0 degrees C reversed cell Na+ and K+ to a mirror image of the normal pattern. Upon rewarming to 37 degrees C the ouabain-sensitive Rb+ uptake became 2-fold faster than the control. A kinetic analysis revealed that the stimulation was due to an increase in the maximal rate of Rb+ uptake, Jmax. The increase in apparent Km was relatively small. The analysis also showed that the ouabain-sensitive cation transport system seemed to have two binding sites for Rb+. The stimulation of Rb+ uptake was related to an increase in cell Na+, and an addition of ouabain abolished such a relation. Net Na+ flux which was in the direction from inside the cells to the medium at hypernormal cell Na+ was iiincreased when cell Na+ ncreased. In contrast, net Na+ flux which was in the opposite direction in the presence of ovabain was reduced and became almost 0 at cell Na+ of 900 nmol/mg of protein. The Na+/Rb+ coupling ratio in the ouabain-sensitive cation transport was apparently less than 1 at nearly physiological cell Na+, but it approached 1.5 when cell Na+ was sufficiently high. The sum of cell K+ plus Rb+ varied inversely with cell Na+, and this relation was unaffected upon treatment with ouabain. When Rb+ uptake declined below 80% of the control, cell K+ plus Rb+ was reduced, however, 40% of the sum of cell cations was still preserved even after complete inhibition of the cation pumps by ouabain treatment of 2 hr. Interrelations of these results are discussed. |
