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Cell Biology International (2003) 27, 921–928 (Printed in Great Britain)

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Comparative NMR studies of diffusional water permeability of red blood cells from different species: XIV. Little Penguin, Eudyptula minor

G.H. Benga¹*, B.E. Chapman², G.C. Cox³ and P.W. Kuchel²

¹Department of Cell and Molecular Biology, “Iuliu Hatieganu” University of Medicine and Pharmacy, 6 Pasteur St, 3400, Cluj-Napoca, Romania
²School of Molecular and Microbial Biosciences, University of Sydney, NSW, Australia
³The Australian Key Center for Microscopy and Microanalysis, University of Sydney, NSW, Australia

Abstract

As part of a programme of comparative measurements of diffusional water permeability (Pd) the red blood cells (RBC) from Little Penguin (Eudyptula minor) were studied. The cell dimensions were measured with light and electron microscopy, and by a newly described non-invasive technique, NMR q-space analysis. In view of its relative novelty for cell biologists, an overview of this technique is presented. The RBC revealed an ellipsoidal shape that is characteristic of avian RBC, with axis lengths (“diameters”) estimated to be: a=16.0 μm; b=9.6 μm; c=5.0 μm. The values of Pdwere: 2.0×10⁻³cm s⁻¹at 5 °C, 3.3×10⁻³cm s⁻¹at 10 °C, 4.6×10⁻³cm s⁻¹at 15 °C and ∼5.4×10⁻³cm s⁻¹at 20, 25, 30, 37 and 42 °C.

There was a lack of inhibition of water permeability by p-chloromercuribenzensulfonate (PCMBS), the well-known inhibitor of RBC aquaporin. It was notable that in the temperature range 5–20 °C the NMR parameters, and hence the permeability, varied linearly as is found for other species, but at temperatures higher than 20 °C there was no temperature-dependence of Pd.Consequently, there was an obvious break at ∼20 °C in the Arrhenius plot, of the mean residence life time of water inside the cells, 1/Te, versus temperature. For temperatures less than 20 °C the activation energy Ea,dwas 45.6±6.6 kJ/mol. For temperatures higher than 25 °C Ea,dwas zero. The lack of inhibition of water permeability by PCMBS and the very high value of Ea,dfor diffusive water exchange suggests that the water permeation occurs primarily via the membrane bilayer per se, i.e., there is no aquaporin in Little Penguin RBC. The discontinuity at ∼20 °C in the Arrhenius plot is an interesting finding, not seen before in other species, and we suggest that it reflects a phase transition in the membrane lipids.

Key words: NMR, Water permeability, Aquaporin, Red blood cells, Little Penguin.

^*Corresponding author. Tel.: +40-64-194373; fax: +40-64-197257

Received 10 October 2002/2 June 2003; accepted 9 July 2003