Vanadate and fluoride activate red cell Na+ permeability by different mechanism.

Fluoride and vanadate are known to induce the Ca(2+)-dependent K+ efflux. We found that both agents concomitantly induced the Ca(2+)-dependent 22Na+ influx. The extent of the Ca(2+)-dependent 22Na+ influx induced by vanadate was very small in human red blood cells but clearly visible in guinea-pig red blood cells. The effect of fluoride has been studied in human red blood cells only. The 22Na+ influx induced by vanadate was inhibited by amiloride but was resistant to tetrodotoxin, whereas that induced by fluoride was resistant to amiloride but sensitive to tetrodotoxin. The effects of inhibitors indicate that vanadate activates the Na/H antiporter and that fluoride opens a tetrodotoxin-sensitive Na+ channel in red blood cells in the Ca(2+)-dependent manner. The results also indicate that both agents activate the Ca(2+)-dependent Na+ permeabilities by unknown auxiliary mechanisms.