Extracellular Na+ inhibits Na+/H+ exchange: cell shrinkage reduces the inhibition
Philip B Dunham1, Scott J Kelley, Paul J Logue
1Department of Biology, Syracuse University, 130 College Place, Syracuse, NY 13244-1220, USA. pbdunham@syr.edu
Abstract:
Na+/H+ exchangers (NHE) are ubiquitous transporters participating in regulation of cell volume and pH. Cell shrinkage, acidification, and growth factors activate NHE by increasing its sensitivity to intracellular H+ concentration. In this study, the kinetics were studied in dog red blood cells of Na+ influx through NHE as a function of external Na+ concentration ([Na+](o)). In cells in isotonic media, [Na+](o) inhibited Na+ influx >40 mM. Osmotic shrinkage activated NHE by reducing this inhibition. In cells in isotonic media + 120 mM sucrose, there was no inhibition, and influx was a hyperbolic function of [Na+](o). The kinetics of Na+-inhibited Na+ influx were analyzed at various extents of osmotic shrinkage. The curves for inhibited Na+ fluxes were sigmoid, indicating more than one Na+ inhibitory site associated with each transporter. Shrinkage significantly increased the Na+ concentration at half-maximal velocity of Na+-inhibited Na+ influx, the mechanism by which shrinkage activates NHE.
Related Concept Videos
Excitatory and Inhibitory Effects of Neurotransmitters
Ligand-Gated Ion Channel Receptor: Gating Mechanism
Resting Potential Decay
At rest, the K+ is the main ion that moves across the membrane through...
Tonicity in Plants
Tonicity in Plants
Tonicity
Tonicity describes the capacity of a cell to lose or gain water depending on the solute...
Adrenergic Neurons: Neurotransmission
Synthesis: Catecholamine synthesis requires tyrosine, which is taken...


