Size and Surface Charge Properties of Myelin Vesicles from Normal and Diseased (Multiple Sclerosis) Brain

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Abstract
Differences have been observed between myelin vesicles prepared from normal human central nervous system and from white matter of patients who died with multiple sclerosis (MS). The mean cross-sectional area of the vesicles was 5.69 ± 0.17 μm2 from normal myelin and 3.71 ± 0.28 μm2 for diseased myelin. Vesicle size was reduced to 4.08 ± 0.21 μm2 when normal myelin vesicles were prepared in the presence of 0.1 mM EDTA. The presence of Ca2 during the preparation of the vesicles had no effect on the mean cross-sectional area. In the case of MS myelin vesicles, 0.1 mM EDTA had no effect on vesicle size, whereas the presence of Ca2+ increased the vesicle size from 3.71 ± 0.28 to 5.40 ± 0.31 μm2 Electrokinetic analysis revealed that the electrophoretic mobility of normal myelin vesicles was -5.169 ± 0.193 × 10−8 compared with -6.093 ± 0.202 × 10−8 m2 s−1 V−1 for the MS myelin vesicles. The presence of 0.1 mM EDTA increased the electrophoretic mobility of the normal vesicles to -6.483 ± 0.151 × 10−8 m2 s−1 V−1 but did not significantly affect that of the MS vesicles. Addition of 0.1 mM Ca2+ decreased the electrophoretic mobility of both normal and MS vesicles to similar mobilities. From these data, the surface charge densities were calculated for both normal and MS myelin vesicles and found to be -2.93 and -5.39 mV m−1 respectively. The phase transition temperature determined by wide angle x-ray diffraction studies was 63°C for normal myelin vesicles and 43°C for MS myelin vesicles. The presence of Ca2 did not affect the phase transition temperature, whereas EDTA decreased it to 40°C in the case of normal myelin vesicles. In the case of MS vesicles, Ca2 increased the phase transition temperature from 43 to 53°C, whereas EDTA had no effect. From these data, we conclude that both the surface properties (surface charge) and the physical structure of the bilayer are affected in MS. The Ca2 concentration of the vesicles from normal myelin was slightly elevated over that of vesicles from MS myelin. The Mg2 concentrations were not significantly different.