LIGHT AND ELECTRON-MICROSCOPIC DETECTION OF ANIONIC SITES IN THE RAT CHOROID-PLEXUS

Electron microscopy of ultrathin sections stained with cationic iron c olloid revealed that, in the choroid plexus of the rat brain ventricle s, the luminal surface and fenestral diaphragm of the capillary endoth elium as well as the basement membranes of the endothelium and epithel ium are strongly anionic or intensely negatively charged. The iron col loid reaction to these anionic sites was erased by treatment with hyal uronidase or digestions with chondroitinase ABC/heparitinase/keratanas e. These results indicate that sulfated proteoglycans provide such ani onic sites of the choroidal capillaries. Discussion suggested that the negative charge on the luminal surface of the capillary endothelium p revents the adhesion of blood cells to capillary walls and also preven ts endothelial adhesion by their repelling each other. It was further discussed that the negatively charged endothelial fenestrae and baseme nt membranes may act as a charge barrier to inhibit the passage of ani onic molecules.