Comparison of urinary excretion of phenolsulfonphthalein in an animal model for Wilson's disease (Long-Evans Cinnamon rats) with that in normal Wistar rats: involvement of primary active organic anion transporter.

PURPOSE: The aim of this study was to determine the cause of the decline in phenolsulfonphthalein (PSP) excretion in Long-Evans Cinnamon (LEC) rats. METHODS: The uptake of PSP into rat renal basolateral membrane vesicles (BLMV) was studied. Cyclosporin A (CYA) was used to modulate an ATP-dependent primary active transporter. PSP was intravenously injected into rats with or without CYA. The transcellular transport of PSP was examined by using primary cultured renal proximal tubule cells (PTC). RESULTS: No significant difference was found between the uptake of PSP into renal BLMV of Wistar rats and that into renal BLMV of LEC rats. In the presence of CYA, the urinary excretion and the plasma concentrations of PSP in Wistar rats were decreased and increased, respectively. In primary cultured renal PTC from Wistar rats, the basal-to-apical transport of PSP was greater than that in the opposite direction and the basal-to-apical transport of PSP was substantially reduced by the addition of CYA. However, CYA did not affect the basal-to-apical transport of PSP in PTC from LEC rats. CONCLUSIONS: The results suggest that PSP is transported by primary active organic anion transporter and that the activity level of this transporter is reduced in LEC rats.

Inhibition by extracellular ATP of organic anion transport in the perfused rat liver.

The action of extracellular ATP on organic anion transport in the bivascularly perfused rat liver was investigated, using bromosulfophthalein as a model substance. Transport was measured by means of the multiple-indicator dilution technique. The action of portal 100 microM ATP presented the following characteristics: (a) inhibition of bromosulfophthalein single pass extraction; the inhibition degree decreased with increasing bromosulfophthalein doses; (b) diminution of the influx rate coefficients; (c) 86.7% decrease of the maximal activity of the saturable component for bromosulfophthalein transport, but 100% increase of the non-saturable component; (d) diminution of the bromosulfophthalein flow-limited distribution space; (e) no significant alteration of the rate coefficients for metabolic sequestration. The action of ATP on organic anion transport in the intact liver occurred at much lower concentrations (10x) than those previously reported for isolated hepatocytes. This reinforces the suggestion that inhibition of organic anion transport could be a physiologically relevant effect of extracellular ATP.

Probenicid inhibition of fluorescence extrusion after MCB-staining of rat-1 fibroblasts.

The intracellular fluorescence level of cells stained continuously with monochlorobimane was monitored by flow cytometry in order to assess the initial rate of glutatione to monochlorobimane conjugation as a measure of glutathione S-transferase activity. In addition to a rapid initial increase and a plateau level, a decline in fluorescence intensity was found upon prolonged flow cytometric monitoring. Exposure to probenicid, an inhibitor of an ATP-dependent organic anion pump, prevented this decrease. Incubation with vanadate and verapamil was without effect. Thus, extrusion of fluorescentglutathione-conjugate perturbs the proportionality between initial glutathione level and monochlorobimane-dependent fluorescence intensity. Monitoring by flow cytometry the decrease in monochlorobimane-dependent fluorescence may be useful to detect multidrug resistant cells.