Human platelet cationic proteins bind to rat glomeruli, induce loss of anionic charges and increase glomerular permeability.

The binding of human platelet cationic proteins (HuPlt CP) to rat renal cortex in vitro and in vivo, the loss of glomerular polyanions (GPA) and the increase in glomerular permeability were studied. HuPlt CP were purified by sequential cation-exchange chromatography and chromatofocusing, by which these proteins were shown to be highly cationic in nature (pI 10.5) and mainly composed of three molecular species of 55.60 kD, 40.45 kD, and 10 kD as studied by gel permeation in high pressure liquid chromatography and SDS-polyacrylamide gel electrophoresis. Binding of HuPlt CP to glomerular capillary walls (GCW), mesangium and to peritubular capillaries of the rat renal cortex was demonstrated by immunofluorescence, using a specific goat anti-HuPlt CP antiserum, after incubation of the sections with HuPlt CP in vitro and after injection of HuPlt CP in vivo. This interaction was ionic in nature, since treatment of sections with heparin abrogated the binding of HuPlt CP to glomerular structures. The glomerular deposits of HuPlt CP were associated with the loss of GPA as revealed by colloidal iron staining (light microscopy) in both in vitro and in vivo experiments and by ruthenium red staining (electron microscopy) in in vivo studies. After the injection of native ferritin, the increase in glomerular permeability produced by an infusion of HuPlt CP was observed by the increased ratio of counted particles within the glomerular basement membrane with respect to controls. The binding of HuPlt CP to GCW and the loss of GPA was consistent with the interpretation that HuPlt CP may increase glomerular permeability due to the neutralization of GPA.