Effect of ammonium chloride on osmotic behavior of red cells in nonelectrolytes

Ammonium chloride, demonstrated to be a permeating electrolyte for human red cells in water or sodium chloride solutions, has been shown to act as if it contributes osmotic support in the presence of sucrose. The additional protection provided by ammonium chloride against hemolysis in hypotonic sucrose was found to approximate the milliosmolar concentration of the added salt. In view of previous suggestions that potassium loss was responsible for the increased protection observed with hypotonic nonelectrolyte alone, it was considered reasonable that the further protection afforded by ammonium chloride might reflect a comparable mechanism. Such a relationship was not observed. When added to isosmotic sucrose, ammonium chloride was found to be as effective as sodium chloride in preventing rather than augmenting potassium loss, in accord with the observations of others. Under hypotonic conditions, however, the addition of ammonium chloride had no effect on potassium loss beyond that observed in hypotonic sucrose alone. Equivalent additions of sodium chloride eliminated the potassium loss entirely. It was concluded that sucrose, and possibly other nonelectrolytes, acted to modify the red cell's permeability to ammonium chloride. It is this conversion of ammonium chloride to an impermeant molecule that is considered to be responsible for the observed osmotic support as well as for the markedly disparate findings in sodium chloride solutions.