Repulsive charge mechanism serve to maintain lumens and cavities. An histochemical study of rat serosa and kidney.

The free surface of the rat peritoneum was covered with a rich negative-charged substance which is distinctly stained with cationic colloidal iron (pH 1.5). Neuraminidase digestion erased this iron stain. Treatment with Limax flavus agglutinin (LFA), which has specific affinity to sialic acid, interferred with iron staining on the serosal surface. Transmission electron microscopy of the peritoneal samples stained with colloidal iron showed that colloidal particles were deposited on the free surface of the mesothelial cells. At pH 1.5, the colloidal particles aggregated in a dotted fashion; in those stained at pH 7.0, the particles arranged in fine strands (100-300 nm in length). This difference may occur as a structural transformation due to pH level changes. The string like structure seemed to correspond well to membrane associated sialomucin. The urinary surface of the rat glomerular podocytes possessed negatively charged sites detectable with cationic colloidal iron even at pH 1.5. Neuraminidase and LFA treatments erased iron staining. Substance containing sialic acid such as podocalyxin on the podocyte surface may be stained. This study shows that negatively charged sites of the substance covering the free surface of these regions repulse each other to maintain the serosal cavities or the podocyte end-feet slits.