Comparative cell shape and diffusional water permeability of red blood cells from Indian elephant (Elephas maximus) and man (Homo sapiens)

Red blood cells (RBC) from act Indian elephant (Elephas maximus) were studi ed by light microscopy (LM), scanning electron microscopy (SEM) and a new n uclear magnetic resonance (NMR) 'imaging' method based on the translational diffusion of water, NMR q-space analysis. Also, the transmembrane diffusio nal permeability, P-d of water in RBC was measured by using a Mn2+-doping N MR technique, taking human RBC as a reference. The main diameter of the ele phant RBC was measured as 9.3 +/- 0.7 mu m by LM, 9.3 +/- 0.7 mu m by 'shri nkage-corrected' SEM, and 9.3 +/- 0.4 mu m by q-space anlaysis. The value i s similar to 1.4 mu m larger than that for the human RBC. The values of P-d were, in the case of elephant RBC, 3.2 x 10(-3) cm/s at 25 degrees C, 3.9 x 10(-3) cm/s at 30 degrees C, 5.2 x 10(-3) cm/s at 37 degrees C and 6.5 x 10(-3) cm/s at 42 degrees C; all values were significantly lower than the c orresponding values of P-d for human RBC, namely 4.3 x 10(-3) cm/s at 25 de grees C, 5.2 x 10(-3) cm/s at 30 degrees C, 6.1 x 10(-3) cm/s at 37 degrees C, 7.8 x 10(-3) cm/s at 42 degrees C. The maximal inhibition of P-d (56%) was reached in 30 min at 37 degrees C with 2 mM p-chloromercuribenzene sulp honate (PCMBS) for both species of RBC. The basal permeability to water at 37 degrees C was estimated to be 2.3 x 10(-3) cm/s for elephant and 2.6 x 1 0(-3) cm/s for human RBC. The values of the activation energy for water per meability (E-a,E-d) was significantly higher for elephant RBC (31.9 kJ/mol) than for human RBC (25.9 kJ/mol). This indicated that features other than the number of transporters per cell are likely to be important in defining the differences in water permeability in the RBC from the two species.