Comparative Nuclear Magnetic Resonance Studies of Diffusional Water Permeability of Red Blood Cells from Different Species. XI. Horses Introduced to Australia and European Horses ( Equus caballus )

The diffusional water permeability (P _d) of red blood cells (RBCs) from horses introduced to Australia and from European horses was measured by a Mn²⁺ doping nuclear magnetic resonance (NMR) technique. The values of P _d were ∼3.5 × 10⁻³ cm/s at 25°C, 4.1 × 10⁻³ cm/s at 30°C, 5.6 × 10⁻³ cm/s at 37°C and 6.3 × 10⁻³ cm/s at 42°C with no significant differences between the two strains of horse. Systematic studies on the effect of p-chloromercuribenzene sulphonate (PCMBS) on water diffusion indicated that the maximal inhibition (60%) was reached in 60 min at 22°C with 1 mm PCMBS. The basal permeability to water was estimated at 1.2 × 10⁻³ cm/s at 25°C, 1.7 × 10⁻³ cm/s at 30°C, 2.0 × 10⁻³ cm/s at 37°C and 2.7 × 10⁻³ cm/s at 42°C. The activation energy (E _a,d) of water diffusion was ∼25 kJ/mol and increased to ∼39 kJ/mol after incubation with PCMBS, in conditions of maximal inhibition of water diffusion. The membrane protein electrophoretic pattern of horse RBCs was compared with its human counterpart. The horse RBC membranes had lower amounts of the proteins migrating as bands 4.1 and 4.2 and higher amounts of the protein migrating as band 4.9, and band 6 (glyceraldehyde-3-phosphate dehydrogenase) was undetectable. A noteworthy feature was the appearance of considerable differences in protein migration distances in the region of bands 7 and 9, between horse and human membranes.