The effect of partial replacements of membrane cholesterol by other steroids on the osmotic fragility and glycerol permeability of erythrocytes

Abstract

1. 1. (A) Sonicated dispersions of lecithins were incubated with aliquots of washed human erythrocytes, leading to the removal of part of the cholesterol complement, eventually followed by lysis. (B) Sonicated dispersions of lecithin and cholesterol with one of a range of other steroids were prepared and incubated with aliquots of washed human erythrocytes. By a simple exchange process, the steroid composition of the erythrocytes were modified. 2. 2. (A) The osmotic fragility of erythrocytes was considerably increased after removal of part of the cholesterol complement with pure lecithin dispersions. (B) The osmotic fragilities of the modified erythrocytes were measured, and it was found that relatively small differences were detectable in view of the substantial replacement of part of the cholesterol with one of the other steroids. 3. 3. Significant differences in the glycerol permeabilities of the modified human and pig erythrocytes were demonstrated. In the presence of 3-ketosteroids, the rates of penetration of glycerol were significantly higher than those containing 3β-hydroxy steroids. Cholesterol-depleted erythrocytes also exhibited considerably increased glycerol permeability.