ULTRASTRUCTURAL-STUDY OF ANIONIC SITES IN GLOMERULAR-BASEMENT-MEMBRANES AT DIFFERENT PERFUSION PRESSURES BY QUICK-FREEZING AND DEEP-ETCHINGMETHOD

The ultrastructures of anionic sites in rat glomerular basement membra nes (GEM) were studied at different perfusion pressures of 100, 150, 2 00 or 250 cm H2O by a quick-freezing and deep-etching (QF-DE) method, in addition to conventional fixation methods, using polyethyleneimine (PEI) as a cationic tracer. By the QF-DE method, three-dimensional ult rastructures at each pressure were observed more clearly than those se en on conventional ultrathin sections. When the perfusion pressures we re changed from low levels to higher ones, the total thickness of GBM with anionic sites became gradually thinner. Many PEI particles were o bserved around filaments, not only in the laminae lucidae, but also in the lamina densa. These findings indicated the existence of anionic s ites in both laminae lucidae and lamina densa of GEM. The numbers of P EI particles in the lamina rara externa were counted on conventional u ltrathin sections for morphometric analyses. The numbers per unit leng th of GBM were significantly decreased at higher perfusion pressures ( 200 and 250 cm H2O) than those seen at both normal (150 cm H2O) and lo wer (100 cm H2O) pressures. It is concluded that the ultrastructures o f anionic sites in the GBM may be changed in vivo, depending on the he modynamics in the glomerular capillary.