Abstract

Comparative morphological and nuclear magnetic resonance (NMR) measurements of the diffusional permeability (P_d) were performed on red blood cells (RBCs) from maternal venous blood and fetal RBCs, isolated from cord blood taken at delivery. Fetal RBC had a diameter of 8.79±0.03 μm (mean±standard deviation, SD), a volume of 103 μm³ and a surface area of 157 μm2. We report here the first comparative measurements of P_d of maternal and fetal RBCs by using a Mn²⁺-doping NMR technique. The values of P_d were, in the case of maternal RBC, 3.7 × 10⁻³ cm/s at 15 °C, 4.1 × 10⁻³ cm/s at 20 °C, 4.9 × 10⁻³ cm/s at 25 °C, 5.2 × 10⁻³ cm/s at 30 °C and 7.2 × 10⁻³ cm/s at 37 °C. For fetal RBC all corresponding P_d values were almost half, namely 2.0 × 10⁻³ cm/s at 15 °C, 2.3 × 10⁻³ cm/s at 20 °C, 2.8 × 10⁻³ cm/s at 25 °C, 3.4 × 10⁻³ cm/s at 30 °C and 4.4 × 10⁻³ cm/s at 37 °C. The decreased P_d values of fetal RBCs were probably due to lower channel-mediated water permeability compared with adult RBCs. The values of the activation energy for water permeability (E_a,d) were significantly higher for fetal RBCs (27.6±5.0 kJ/mol) than for adult RBCs (22.8±2.7 kJ/mol). A positive correlation between the P_d values of the two kinds of RBCs was found. This points to the genetic basis for the determination of RBC water permeability.