SODIUM INTERACTION WITH ORDERED STRUCTURES IN MAMMALIAN RED-BLOOD-CELLS DETECTED BY NA-23 DOUBLE QUANTUM NMR

Na-23 double and triple quantum filtered NMR spectra of intact dog and human red blood cells were measured with the pulse sequence rees-tau/ 2-theta-degrees-t1-theta-degrees-t2(Acq). For theta = 900 the triple q uantum filtered spectra exhibited the typical multiple quantum filtere d lineshape, characteristic of isotropic media, while the double quant um filtered ones presented a superposition of two signals, whose propo rtion depended on the creation time tau. This effect is due to the for mation of both second and third rank tensors. The formation of the sec ond rank tensor, T21 results from non-zero residual quadrupolar intera ction and is related to the anisotropic motion of sodium ions. Measure ments of the double quantum filtered spectra with theta = 54.7-degrees enabled the detection of the contribution of T21 exclusively. No resi dual quadrupolar interaction was detected for sodium in the cytoplasm, while unsealed ghosts displayed the double quantum filtered spectral pattern, similar to that of intact cells. The anisotropy of motion of the sodium at the plasma membrane of mammalian erythrocytes depended o n the integrity of the cytoskeleton network. Theoretical analysis of t he double quantum filtered spectra gave a value of residual quadrupola r splitting of approximately 20 Hz for intact unsealed ghosts. The dat a presented prove that double quantum filtering is a sensitive techniq ue for detection of motional anisotropies in biological systems.