DIFFERENTIAL PROPERTIES OF BRUSH-BORDER MEMBRANE-VESICLES FROM EARLY AND LATE PROXIMAL TUBULES OF RAT-KIDNEY

We describe the preparation and properties of BBM vesicles (BBMV) from the superficial and juxtamedullary rat renal cortex using Ca2+-precip itation method and/or by density gradient centrifugation. BBMV were ch aracterized by the presence of BBM marker enzymes as distributed along microdissected proximal convoluted tubule and proximal straight tubul es from superficial and juxtamedullary cortex. In tubules from both su perficial and juxtamedullary cortex, the activities of gamma-glutamylt ransferase and leucine aminopeptidase were 5-10 times higher in proxim al straight tubules than in proximal convoluted tubule. The alkaline p hosphatase was higher in proximal convoluted tubules than in straight tubules from superficial cortex, but it was lower in proximal convolut ed than straight tubules from the juxtamedullary cortex. The Na+/P-i c otransport had higher V-max and lower K-m in BBMV from superficial cor tex than from BBMV from juxtamedullary tissue. BBMV from superficial c ortex separated on Percoll gradient showed a high activity of alkaline phosphatase and low activities of gamma-glutamyltransferase and leuci ne aminopeptidase. Conversely, BBM from juxtamedullary cortex separate d into a major peak with very high activities of gamma-glutamyltransfe rase and leucine aminopeptidase, and lesser activity of alkaline phosp hatase. These distinct BBMV fractions showed diverse Na+/P-i cotranspo rt properties and BBM marker enzyme distributions. Thus, using the out lined methodology it is feasible to prepare BBMV derived predominantly from proximal convoluted tubules or from proximal straight tubules lo cated in either superficial or deep cortical nephrons.