Effects of p-chloromercuribenzene sulfonate on water transport across the marsupial erythrocyte membrane

The effects of exposure of red blood cells (RBC) of three species of marsupial to a mercury-containing sulfhydryl-modifying reagent, p-chloromercuribenzene sulfonate (PCMBS), on the water diffusional permeability (Pd) of their membranes were monitored by using an Mn2+-doping 1H nuclear magnetic resonance (NMR) technique at 400 MHz. For koala (Phascolarctos cinereus), RBC the maximal inhibition was reached at 37 °C in 60 min with 1 mmol.l–1 PCMBS or in 15–30 min with 2 mmol. l–1 PCMBS. In contrast, in the case of red kangaroo (Macropus rufus) or swamp wallaby (Wallabia bicolor) RBC, maximal inhibition required an incubation of 90 min at 37 °C with 2 mmol.l–1 PCMBS. For the RBC of all three species the value of maximal inhibition was very high, being 50–70% when measured at 25 °C, 60–80% at 30 °C and 60–70% at 37 °C. The lowest values of Pd appeared to be around 2×10–3–3×10–3 cm.s–1 in the temperature range of 25–37 °C. The mean value of the activation energy of water diffusion (Ea,d) was ~20–25 kJ.mol–1 for control and ~40 kJ.mol–1 for PCMBS-inhibited RBCs. These results show that marsupial RBC have a basal permeability to water similar to that previously reported for human RBC, but a higher value of the PCMBS-inhibitable water permeability. This indicates that the higher water permeability of marsupial RBC compared with human RBC is associated with a higher fraction of protein-mediated water permeability.