Printed in Great Britain THE SURFACE STRUCTURE OF CULTURED RABBIT KIDNEY CELLS AS REVEALED BY ELECTRON MICROSCOPY

An epithelioid line of rabbit kidney cells (RK 13), in which the distribution of blood group antigen A had previously been investigated by mixed agglutination, was chosen for studies of the structure of the cell surface. Cells were grown in monolayer culture, and thin sections were examined by electron microscopy after fixation in glutaraldehyde and osmium tetroxide and staining of the sections with lead, or uranyl and lead. Cells were also treated with ruthenium red incorporated in the osmium fixative. Other cells were fixed in lanthanum or potassium permanganate, and both stained and unstained sections were examined. The morphology of RK / j cell surfaces is described. There is apparently no great degree of cellular specialization. The treatment with ruthenium red resulted in dense staining of a layer of the cell surface that is not visible in conventional preparations, and sometimes in staining of the surfaces of intracellular organelles. Lanthanum permanganate fixation also revealed a dense layer on the surface of the plasma membrane; a less dense surface layer was distinguished in many cells fixed in potassium permanganate. The reaction of ruthenium red with the cell surface is probably due to the presence of acidic glycoproteins, but the chemical specificity of the staining method is not yet clear. The nature of the material revealed by lanthanum and potassium permanaganates is also undefined. How-ever, these staining methods reveal that the cell surface is more complex than is apparent in cells prepared by conventional techniques. The additional surface layer is probably the site of many blood group substances and other compounds involved in the physiological reactions of the cell surface