title: Digital fluorescence imaging of organic cation transport in freshly isolated rat proximal tubules.
abstract: The secretion of cationic drugs and endogenous metabolites is a major function of the kidney. This is accomplished by organic cation transport systems, mainly located in the proximal tubules. Here, we describe a model for continuous measurement of organic cation (OC) transport. In this model, organic cation transport in individual freshly isolated rat proximal tubules is investigated by use of digital fluorescence imaging. To directly measure organic cation transport across the basolateral membrane, the fluorescent organic cation 4-(4-dimethylaminostyryl)-N-methylpyridinium (ASP+) is used with a customized perfusion chamber. ASP+ uptake in this model displayed the characteristics of organic cation transport. Over the tested range of 1 to 50 microM, it showed a concentration-dependent uptake across the basolateral membrane. In the presence of competitive inhibitors of OC transport such as N1-methylnicotinamide+, tetraethylammonium+, and choline+, a concentration-dependent and reversible inhibition of ASP+ uptake could be documented. In conclusion, continuous measurement of organic cation transport in freshly isolated rat proximal tubules by digital fluorescence imaging using ASP+ is a useful tool for investigation of drug transport and interactions and, furthermore, may be helpful for investigation of organic cation transport under pathophysiological conditions.
authors.affiliation: Department of Nephrology, School of Medicine, University Hospital, Essen, Germany. frank.pietruck@uni-essen.de
authors.forename: Frank
authors.initials: F
authors.lastname: Pietruck
authors.forename: Markus
authors.initials: M
authors.lastname: Horbelt
authors.forename: Thorsten
authors.initials: T
authors.lastname: Feldkamp
authors.forename: Katrin
authors.initials: K
authors.lastname: Engeln
authors.forename: Stefan
authors.initials: S
authors.lastname: Herget-Rosenthal
authors.forename: Thomas
authors.initials: T
authors.lastname: Philipp
authors.forename: Andreas
authors.initials: A
authors.lastname: Kribben
mesh_terms: D000818:Animals; D001692:Biological Transport; D002412:Cations; D004305:Dose-Response Relationship, Drug; D005456:Fluorescent Dyes / Q000493:pharmacokinetics*; D007090:Image Interpretation, Computer-Assisted; D066298:In Vitro Techniques; D007687:Kidney Tubules, Proximal / Q000378:metabolism*; D008297:Male; D008856:Microscopy, Fluorescence; D011726:Pyridinium Compounds / Q000493:pharmacokinetics*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: C032315:4-(4-dimethylaminostyryl)-1-methylpyridinium; D002412:Cations; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds