Multiple pathways of organic anion secretion in renal proximal
tubule revealed by confocal microscopy.
Masereeuw, Rosalinde, Frans G. M. Russel, and David S. Miller.
Department of Pharmacology, Faculty of Medical Sciences, University
of Nijmegen, Nijmegen, The Netherlands, Intracellular Regulation
Section, Laboratory of Pharmacology and Chemistry, National Institute
of Environmental Health Sciences, National Institutes of Health,
Research Triangle Park, North Carolina 27709
APStracts 3:0164F, 1996.
Previous studies with p-aminohippurate (PAH) and fluorescein (FL),
have shown that cellular uptake and tubular secretion of organic
anions is driven by indirect coupling to sodium. Here we used
killifish proximal tubules and laser scanning confocal microscopy to
study the transport of a larger organic anion, fluorescein
-methotrexate (FL-MTX, Mw 923 Da). When tubules were incubated in
medium containing 2 [mu]M FL-MTX, dye accumulated in both cells and
tubular lumens. At steady-state, lumenal fluorescence was 4-5 times
higher than cellular fluorescence. Ouabain (0.1 mM) did not affect
cellular or lumenal fluorescence, and replacement of medium sodium by
N-methylglucamine had only a modest effect; preincubation with
glutarate had no effect. KCN did not affect cellular uptake but
abolished secretion into the lumen. Uptake and secretion of FL-MTX
was inhibited by micromolar concentrations of other organic anions
(MTX, folate, probenecid, bromocresol green, BSP), but 1 mM PAH had a
relatively small effect. FL- MTX secretion into the lumen was
inhibited by leukotriene C4, cyclosporine A and verapamil, none of
which affected FL transport. Thus, a substantial component of FL-MTX
secretion is Na- independent and ouabain-insensitive. Both the
basolateral and luminal steps in the Na-independent pathway differ
from those usually associated with FL and PAH secretion.
Received 7 June 1996; accepted in final form 29 August 1996.
APS Manuscript Number F166-6.
Article publication pending Am. J. Physiol. (Renal Fluid Electrolyte
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 19 September 1996