Uptake and trafficking of fluorescent conjugates of folic acid in intact kidney determined using intravital two-photon microscopy

Ruben M. Sandoval, Michael D. Kennedy, Philip S. Low, Bruce A. Molitoris

Research output: Contribution to journalArticle

114 Scopus citations

Abstract

Intravital two-photon microscopy was used to follow the uptake and trafficking of fluorescent conjugates of folic acid in the rat kidney. Intravenously administered folate-linked dye molecules quickly filled the plasma volume but not cellular components of the blood. Glomerular filtration occurred immediately and binding to proximal tubule cells was seen within seconds. Fluorescence from a pH-insensitive conjugate of folic acid, folate Texas red (FTR), was readily observed on the apical surface of the proximal tubules and in multiple cellular compartments, but little binding or uptake could be detected in any other kidney cells. Fluorescence from a pH-sensitive conjugate of folic acid, folate fluorescein, was seen only on the apical surface of proximal tubule cells, suggesting that internalized folate conjugates are localized to acidic compartments. The majority of the FTR conjugate internalized by proximal tubules accumulated within a lysosomal pool, as determined by colocalization studies. However, portions of FTR were also shown by electron microscopy to undergo transcytosis from apical to basal domains. Additional studies with colchicine, which is known to depolymerize microtubules and interrupt transcytosis, produced a marked reduction in endocytosis of FTR, with accumulation limited to the subapical region of the cell. No evidence of cytosolic release of either folate conjugate was observed, which may represent a key difference from the cytosolic deposition seen in neoplastic cells. Together, these data support the argument that folate conjugates (and, by extrapolation, physiological folate) bind to the apical surface of proximal tubule cells and are transported into and across the cells in endocytic compartments.

Original languageEnglish (US)
Pages (from-to)C517-C526
JournalAmerican Journal of Physiology - Cell Physiology
Volume287
Issue number2 56-2
DOIs
StatePublished - Aug 1 2004

Keywords

  • Proximal tubule cell

ASJC Scopus subject areas

  • Clinical Biochemistry
  • Cell Biology
  • Physiology

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