Hydraulic permeability coefficients of individual human erythrocytes

Abstract

The hydraulic permeability coefficients of individual human erythrocytes were calculated from their rate of swelling to hemolysis as observed using microcinéphotography. Cells suspended in 10 mM Tris–HCl buffered Ringer solution (pH 7.40, 310 mosmol) were hemolyzed with hypotonic NaCl solutions ranging from 20 to 100 mosmol. The hemolysis, swelling, stress, potassium-leak, and hemoglobin-leak times all increased with increasing external impermeant concentration, but the relative magnitude of each stage of hemolysis remained unchanged. Of the total hemolysis time, swelling time only accounted for 20% while the stress time made up 80%. The stress time was further analyzed as potassium-leak and hemoglobin-leak times, which amounted to 22 and 58%, respectively. Permeability coefficients of individual erythrocytes ranged from 1.5 × 10−3 to 18.6 × 10−3 cm/s. The variation within a cell population represented a skewed normal distribution in each case of hemolysis by different solutions. The mean hydraulic permeability coefficient increased from 4.24 × 10−3 to 9.24 × 10−3 cm/s as external impermeant concentration decreased from 100 to 20 mosmol. Extrapolation of experimental data gave a value of 1.2 × 10−2 cm/s for water hemolysis at pH 7.40. This corresponds to a mean swelling time of 0.5 s. The permeability coefficient obtained with hemolysis by unbuffered (pH 6.0) distilled water gave a lower value of 7.34 × 10−3 cm/s. The discrepancy may be due to a possible effect of Tris on the cell membrane or it may be a result of a pH dependence of the membrane permeability coefficient. The dependence of mean hydraulic permeability on osmotic pressure has previously been explained as due to rectification of water flow across the cell membrane, but it may also be due to a dependence on membrane hydration and area changes in response to osmotic pressure as observed in a related study. The present study provides measurements of not only the mean hydraulic permeability coefficient for the red cell but also the range and distribution of permeabilities of individual cells within the cell population.