Morphological heterogeneity of isolated renal basement membranes.

Abstract

The mammalian renal cortex is composed primarily of epithelial structures. These include renal corpuscles, tubules, and vascular components bounded by basement membranes and supported by extracellular matrix. In an effort to elucidate the morphological characteristics of these materials, we carried out a comparative electron microscopic study of the acellular renal cortex in the rabbit, rat, rhesus monkey, and human. Acellular tissue blocks were prepared as described elsewhere in this symposium <i>[Carlson and Kenney: </i>‘Preparation and histoarchitecture of ultrastructurally pure glomerular basement membrane’]. In addition, basement membranes were isolated from purified fractions of renal tubules and glomeruli. Light microscopic studies of rabbit and rat acellular renal cortex showed that the extracellular matrix was less dense and basement membrane more delicate than those seen in either monkey or human. By electron microscopy, the renal interstitium demonstrated several major basement membrane types. These included tubular, peritubular capillary, Bowman’s capsular and glomerular basement membranes, all of which contributed to the delimitation of an uncompartmented connective tissue space. The thickness of basement membranes varies but usually human monkey rat rabbit. Tubular basement membranes were thicker than glomerular basement membranes (TBM/GBM = 2.3–2.7) with the differential least in rat and highest in rabbit. Paradoxically, isolated tubular basement membrane showed less structural rigidity than glomerular basement membranes. Further non-uniformity of individual basement membranes was demonstrated by enzyme digestion (trypsin and pepsin) of mixtures of isolated tubular and glomerular basement membranes. These showed that glomerular basement membrane was much less susceptible to enzyme solubilization than adjacent tubular basement membrane. Furthermore, the endothelial-mesangial surface of glomerular basement membranes endothelial-mesangial surface of glomerular basement membranes and the connective tissue surface of tubular basement membranes were preferentially digested by the enzymes, indicating a possible ‘sidedness’. In addition, variable surface-associated substances were demonstrated by treatment with ruthenium red which preferentially stained both surfaces of glomerular basement membranes while adjacent Bowman’s capsule and tubular basement membrane remained unstained. We conclude that the diversity of substructure in various basement membranes strongly favors a ‘nonunitary concept’ of these matrices and generally supports the idea that they are compositionally heterogeneous.