Daunomycin secretion by killifish renal proximal tubules. Miller, David S. Intracellular Regulation Section, Laboratory of Cellular and Molecular Pharmacology, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, North Carolina 27709
APStracts 2:0067R, 1995.
Epi-fluorescence microscopy and video image analysis were used to measure the uptake of the fluorescent anthracycline, daunomycin, by intact, killifish renal proximal tubules. When tubules were incubated in medium containing 2-5 [mu]M daunomycin, the drug accumulated in both the cells and tubular lumen. At steady-state, lumenal fluorescence was 2-3 times greater than cellular. Lumenal accumulation of daunomycin was reduced when tubules were exposed to the multidrug resistance (MDR) transporter modifiers, verapamil and cyclosporin A (CSA), but not tetraethylammonium (TEA), a model substrate for the renal organic cation transport system. Both NaCN and vanadate reduced lumenal drug accumulation. In contrast, cellular daunomycin accumulation was not affected by verapamil, CSA, TEA or vanadate, and only slightly reduced by NaCN. When the pH of the buffer solution was decreased from 8.25 to 7.25, lumenal, but not cellular, accumulation of daunomycin was again reduced by CSA, however, TEA now reduced cellular and lumenal accumulation. These findings are consistent with daunomycin being actively secreted in killifish proximal tubule by two mechanisms. At pH 8.25, daunomycin crossed the basolateral membrane by simple diffusion and was secreted into the tubular lumen by the MDR transporter. At pH 7.25, daunomycin was transported across the basolateral membrane by both simple diffusion and carrier mediated uptake on the organic cation transporter and was secreted into the lumen by the MDR transporter and the organic cation-H+ exchanger. 

Received 31 March 1994; accepted in final form 28 February 1995.
APS Manuscript Number R162-4.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.