Characterization of the β2-microglobulin endocytic pathway in rat proximal tubule cells

D. P. Sundin, M. Cohen, R. Dahl, S. Falk, B. A. Molitoris

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22 Scopus citations


The uptake mechanism(s) of low-molecular-weight proteins by proximal tubule cells remains incompletely characterized. We utilized a biochemical and semiquantitative morphological approach to better characterize the endocytic pathway of an anionic protein, β2-microglobulin (β2M), in the rat proximal tubule. Indirect immunogold techniques revealed β2M was taken up via a classic receptor-mediated endocytic pathway. In vitro biochemical and morphological characterization of iodinated β2M and gold-conjugated β2M (gold-β2M) binding to isolated brush-border membrane vesicles (BBMV) documented specific and quantitatively similar binding interactions of the modified β2M with BBMV. Kinetic characterization of the in vivo endocytic pathway of gold-β2M was undertaken using microinfusion of individual tubules. β2M initially bound at the apical surface, was internalized into subapical coated vesicles and delivered to endosomal-like structures within 5 min, and, finally, was concentrated in lysosomal-like structures within 15 min. This uptake was inhibited by excess unconjugated β2M. In addition, we directly showed that uptake did not occur across the basolateral surface. Finally, by passing solubilized BBMV over β2M affinity columns we were able to isolate binding activity.

Original languageEnglish (US)
Pages (from-to)F380-F389
JournalAmerican Journal of Physiology - Renal Fluid and Electrolyte Physiology
Issue number3 36-3
StatePublished - 1994


  • low-molecular-weight protein uptake
  • receptor isolation
  • β- microglobulin modification

ASJC Scopus subject areas

  • Physiology

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