Preservation of renal brush border membrane transport function by storage in glycerol

Abstract

Various methods for the isolation of renal and intestinal brush border membranes have been reported [1]. The isolated membranes vesiculate and are used as model systems to examine the mechanisms by which solutes, for example, sugar and amino acids, are transported into the epithelial cell [2, 3]. Although these studies have provided valuable insight into the transport systems, their general applicability has been limited because of the necessity to measure uptakes on the same day that the membranes are prepared [4], the time required to prepare the membranes being often as long as 5 to 6 hr [5, 6], and the large numbers of small animals (e.g. 20 rats) needed for each preparation [6]. Moreover, the relatively small yield of brush border membranes with each preparation severely hampers efforts to purify sugar and amino acid carriers since the only assay for the carrier in membrane reconstitution studies is transport function itself, rather than catalytic activity, as with cation transporting adenosine triphosphatases [7]. Thus, a procedure for preserving transport function of these membranes is critically needed. Because glycerol and low temperature have been used in other systems to maintain cell integrity and biologic function [8], this technique was examined with isolated renal brush border membranes. In this communication, the preservation of D-glucose and L-proline transport function in stored membranes is reported.