Surface charge of eosinophils. Binding of cationic particles and measurement of cellular electrophoretic mobility

The surface charge of eosinophils, isolated from the peritoneal exudate of rats by the use of a Metrizamide gradient, was analysed by ultrastructural cytochemistry and cellular electrophoretic mobility. Binding of colloidal iron hydroxide and of cationized ferritin particles at pH 1.8 and 7.2 respectively, was observed on the surface of the eosinophils. An electrophoretic mobility of -1.08 and -1.39 micrometer.s-1.V-1.cm was determined for living and glutaraldehyde-fixed eosinophils, respectively. Treatment of the cells with neuraminidase reduced the electrophoretic mobility to -0.64 micrometer.s-1.V-1.cm (glutaraldehyde-fixed), reduced significantly and abolished completely the binding of both colloidal iron hydroxide and cationized ferritin particles to the surface of the cells. These results indicate that sialic acid exists on the surface of eosinophils, where it accounts for part of the negative surface charge.