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NMR studies of diffusional water permeability of red blood cells from macropodid marsupials (kangaroos and wallabies)
G Benga1, B E Chapman, C H Gallagher
1Department of Biochemistry, University of Sydney, NSW, Australia.
Abstract:
1. The water permeabilities of the red blood cell (RBC) membranes of five species of macropodid marsupials were monitored by using a Mn(2+)-doping 1H nuclear magnetic resonance (NMR) technique. 2. Since this appears to be the first time that this type of measurement at 400 MHz for 1H has been reported, an analysis of instrumental parameters influencing the estimated value of the water exchange time (Te), and of the diffusional water permeability (Pd), was performed on samples of human RBC. 3. It was found that a short interpulse delay in the Carr-Purcell-Meiboom-Gill pulse sequence had to be used (around 100 microseconds) to avoid an underestimation of the relaxation times, that occurred as the result of molecular diffusion through non-uniform local magnetic fields in and around the cells. 4. There were no significant differences, in the water permeabilities of the RBC membranes, between the five species (Macropus rufogriseus, M. parma, M. eugenii, M. parryi and Wallabia bicolor). 5. There were also no significant differences between various colonies of M. eugenii living in different habitats. 6. The average values of Pd were 9.1 x 10(-3) cm/sec at 24.6 degrees C, 10.4 x 10(-3) cm/sec at 30 degrees C, 12.6 x 10(-3) cm/sec at 37 degrees C, and 14.7 x 10(-3) cm/sec at 42.1 degrees C; these were more than twice as high as those for human RBC. 7. In agreement with the high water permeability the RBC of macropodids displayed a relatively low activation energy of water diffusion across their membranes, approximately 21 kJ/mol, compared with 25 kJ/mol for human RBC.
Insights
Red blood cell (RBC) water permeability in macropodid marsupials was measured using nuclear magnetic resonance (NMR). Macropodid RBCs showed significantly higher water permeability than human RBCs, with no interspecies differences observed.
Area of Science:
- Biophysics
- Cell Biology
- Comparative Physiology
Background:
- Red blood cell (RBC) membrane water transport is crucial for cell function.
- Nuclear magnetic resonance (NMR) spectroscopy offers a non-invasive method to study water dynamics across membranes.
- Macropodid marsupials possess unique physiological adaptations, warranting investigation into their RBC membrane properties.
Purpose of the Study:
- To quantify the water permeability of RBC membranes in five species of macropodid marsupials.
- To compare macropodid RBC water permeability with that of human RBCs.
- To analyze instrumental parameters affecting NMR measurements of water exchange time and permeability.
Main Methods:
- Utilized a Mn(2+)-doping 1H nuclear magnetic resonance (NMR) technique at 400 MHz.
- Optimized instrumental parameters, including Carr-Purcell-Meiboom-Gill pulse sequence interpulse delay, for accurate relaxation time measurements.
- Measured diffusional water permeability (Pd) and water exchange time (Te) in RBCs from five macropodid species and human controls.
Main Results:
- No significant differences in RBC water permeability were found among the five macropodid species or between different colonies of Macropus eugenii.
- Macropodid RBCs exhibited water permeabilities (Pd) more than twice as high as human RBCs across a range of temperatures.
- The activation energy for water diffusion across macropodid RBC membranes was lower (approx. 21 kJ/mol) than for human RBCs (25 kJ/mol).
Conclusions:
- Macropodid marsupials possess exceptionally high red blood cell water permeability compared to humans.
- This high permeability is consistent with a lower activation energy for water diffusion, suggesting efficient water transport mechanisms.
- The findings provide insights into the biophysical properties of marsupial erythrocyte membranes and their physiological implications.
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