EXTRALYSOSOMAL LOCALIZATION OF ACID-PHOSPHATASE IN THE RAT-KIDNEY

There is strong evidence that acid phosphatase (AcPase) plays an impor tant role in the catabolism of the glomerular basement membrane (GEM) and the removal of macromolecular debris resulting from ultrafiltratio n. Recent enzyme histochemical investigations provide new evidence of the antithrombotic and anti-inflammatory function of ADPase and on the distribution of AcPase in mouse kidney tubule cells. By means of 3 mM cerium as the trapping agent and 1 mM p-nitrophenyl phosphate as the substrate, extralysosomal AcPase could be demonstrated at the ultrastr uctural level. Following a mild per fusion fixation (2% formaldehyde 0.07% glutaraldehyde), an effective postfixation and short enzyme inc ubations (20 min) with microwave irradiation, highly specific enzyme h istochemical reaction product and reasonable structural preservation w ere obtained. Extralysosomal, membrane-bound AcPase was observed along the endoplasmic reticulum, the trans-Golgi cisternae, the nuclear env elope, basal infoldings of the proximal and distal tubular cells and o n glomerular profiles, e.g. cell membranes of podocytes, endothelium a nd basement membrane. Large amounts of extralysosomal AcPase were obse rved in the basement membrane of glomeruli, in contrast to no AcPase a ctivity in the tubular and mesangial basement membrane. The observed d ifference in AcPase activity in the tubular epithelial basement membra ne and the GEM supports the idea that AcPase in GEM specifically serve s in the clearance of macromolecular debris to facilitate ultrafiltrat ion. In the GEM a laminar distribution is observed, suggesting that bo th epithelial and endothelial cells are involved in the production of AcPase.