AJP - Cell Physiology, Vol 249, Issue 1 63-C68, Copyright © 1985 by American Physiological Society
Absence of significant sodium-hydrogen exchange by rabbit erythrocyte sodium-lithium countertransporter
M. L. Jennings, M. Adams-Lackey and K. W. Cook
Red blood cells of several mammalian species (e.g., human, rabbit, bovine)
possess a countertransport system for Li and Na. We have used rabbit red
blood cells to determine the extent of sodium-proton exchange by this
countertransporter. Ouabain-insensitive 22Na efflux into phosphate-buffered
K-acetate media of varying Na concentrations was determined at
extracellular pH 7.5 and 6.9. To maintain the intracellular pH at
approximately 7.2, most of the acetate in the pH 6.9 medium was replaced by
gluconate, a nonpenetrating anion. Extracellular Na strongly (greater than
10-fold) stimulated the 22Na efflux in both high- and low-pH media, but the
K1/2 for this stimulation was higher at pH 6.9. This is consistent with a
competitive binding of H to the outward-facing transport site. However, the
lower pH itself, in a Na-free medium, stimulated the 22Na efflux only very
slightly. The 22Na efflux stimulated by lowering the extracellular pH to
6.9 was less than 1% of the stimulation produced by 100 mM extracellular
Na. It is concluded that, although H appears to bind to the substrate site
of the Na-Li exchanger, there is no significant H transport in the
physiological pH range.
