Differential properties of brush-border membrane vesicles from early and late proximal tubules of rat kidney.

ABSTRACT

We describe the preparation and properties of BBM vesicles (BBMV) from the superficial and juxtamedullary rat renal cortex using Ca(2+)-precipitation method and/or by density gradient centrifugation. BBMV were characterized by the presence of BBM marker enzymes as distributed along microdissected proximal convoluted tubule and proximal straight tubules from superficial and juxtamedullary cortex. In tubules from both superficial and juxtamedullary cortex, the activities of gamma-glutamyltransferase and leucine aminopeptidase were 5-10 times higher in proximal straight tubules than in proximal convoluted tubule. The alkaline phosphatase was higher in proximal convoluted tubules than in straight tubules from superficial cortex, but it was lower in proximal convoluted than straight tubules from the juxtamedullary cortex. The Na+/Pi cotransport had higher Vmax and lower Km in BBMV from superficial cortex than from BBMV from juxtamedullary tissue. BBMV from superficial cortex separated on Percoll gradient showed a high activity of alkaline phosphatase and low activities of gamma-glutamyltransferase and leucine aminopeptidase. Conversely, BBM from juxtamedullary cortex separated into a major peak with very high activities of gamma-glutamyltransferase and leucine aminopeptidase, and lesser activity of alkaline phosphatase. These distinct BBMV fractions showed diverse Na+/Pi cotransport properties and BBM marker enzyme distributions. Thus, using the outlined methodology it is feasible to prepare BBMV derived predominantly from proximal convoluted tubules or from proximal straight tubules located in either superficial or deep cortical nephrons.