PERMEABILITY OF INDIVIDUAL HUMAN ERYTHROCYTES TO THIOUREA

The osmotic swelling to hemolysis of individual red blood cells by isosmotic thiourea was studied using microcine photography. Crenation occurs immediately upon addition of isosmotic thiourea. The cell becomes a crenated sphere without volume decrease. Subsequently, the cell volume increases linearly with time with maximum swelling occurring at about 102 s, which is 81% of the total hemolysis time. At maximum swelling, the cell volume is 92% greater than the initial cell volume. This volume increase is about double that measured with other permeating substances. The much larger maximum volume implies that thiourea increases the area of the cell membrane. Membrane expansion varies inversely as the initial cell membrane area and cell volume (r = 0.790). Using the increased surface area, increased maximum volume and the swelling time, the mean permeability is calculated to be 5.52 .times. 10-7 cm/s (SD of mean = .+-. 1.19 .times. 10-7 cm/s). The pre-lytic K loss ranged from 0-36% with a mean value of 16.5%. Membrane permeability of individual cells varies with the amount of membrane expansion observed. Coefficient of correlation between permeability and expansion index is 0.674. There is no correlation between permeability and the reciprocal of the hemolysis time (r = -0.035). The correlation between permeability and the reciprocal of the swelling time is also poor (r = 0.303), probably owing to the variability in membrane expansion by thiourea in individual cells. As was shown previously for faster permeants, the permeability coefficient cannot be calculated from the hemolysis time. Because thiourea alters the membrane area and the hemolytic volume, the coefficient cannot be calculated from the swelling time unless the changes in the membrane area are also taken into account.