On the mechanism of sodium-proton exchange in crayfish

In salt depleted crayfish net sodium and proton fluxes were coupled 1:1 as required by the frog skin-turtle bladder model. In addition, three proton pump inhibitors produced equal reductions of both fluxes. It is concluded that the model operates in these animals. Net Na+ and H+ fluxes were very small in tap water adapted animals, but regression analysis clearly showed that they were coupled, though perhaps not 1:1. Proton pump inhibitors, at concentrations that suppressed fluxes in salt-depleted crayfish, had no measureable effect on proton movement in tap water-adapted animals. Two of them (dicyclocarbodiimide and N-ethyl maleimide), caused a small reduction in Na+ influx without affecting proton efflux. These experiments provide no support for operation of the frog-turtle system in adult crayfish adapted to tap water. A 2Na+-H+ exchanger is considered from an energetic point of view. Such a system might be able to couple Na+ and H+ fluxes in dilute, near neutral solutions ([Na+] approximately 1-2 mM; pH 7).