Water Permeability of Chlorella Cell Membranes by Nuclear Magnetic Resonance

Abstract

Measurement by 2 NMR techniques of the mean residence time .tau.a of water molecules inside C. vulgaris (Beijerinck) var. viridis (Chodot) is reported. The first is the Conlon and Outhred technique in which extracellular water is doped with paramagnetic Mn2+. Some complications in application of this technique are identified as being caused by the affinity of Chlorella cell walls for Mn2+ which shortens the NMR relaxation times of intra- and extracellular water. The second is based upon observations of effects of diffusion on the spin echo of intra- and extracellular water. Echo attenuation of intracellular water is distinguished from that of extracellular water by the extent to which diffusive motion is restricted. Intracellular water, being restricted to the cell volume, suffers less echo attenuation. From the dependence of echo amplitude upon gradient strength at several values of echo time, the mean residence time of intracellular water was determined. From the mean residence time of intracellular water, the diffusional water permeability coefficient of the Chlorella membrane is calculated to be 2.1 .+-. 0.4 .times. 10-3 cm s-1.