Proteomic analysis of brush-border membrane vesicles isolated from purified proximal convoluted tubules

The renal proximal convoluted tubule is the primary site of water, electrolyte and nutrient reabsorption and of active secretion of selected molecules. Proteins in the apical brush-border membrane facilitate these functions and initiate some of the cellular responses to altered renal physiology. The current study uses two-dimensional liquid chromatography/mass spectrometry to compare brush border membrane vesicles isolated from rat renal cortex (BBMVCTX) and from purified proximal convoluted tubules (BBMVPCT). Both proteomic data and Western blot analysis indicate that the BBMVCTXcontain apical membrane proteins from cortical cells other than the proximal tubule. This heterogeneity was greatly reduced in the BBMVPCT. Proteomic analysis identified 193 proteins common to both samples, 21 proteins unique to BBMVCTX, and 57 proteins unique to BBMVPCT. Spectral counts were used to quantify relative differences in protein abundance. This analysis identified 42 and 50 proteins that are significantly enriched (p values ≤0.001) in the BBMVCTXand BBMVPCT, respectively. These data were validated by measurement of γ-glutamyltranspeptidase activity and by Western blot analysis. The combined results establish that BBMVPCTare primarily derived from the proximal convoluted tubule (S1 and S2 segments), whereas BBMVCTXinclude proteins from the proximal straight tubule (S3 segment). Analysis of functional annotations indicated that BBMVPCTare enriched in mitochondrial proteins and enzymes involved in glucose and organic acid metabolism. Thus the current study reports a detailed proteomic analysis of the brush-border membrane of the rat renal proximal convoluted tubule and provides a database for future hypothesis-driven research.