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  • 1
    ISSN: 1432-2013
    Keywords: Dicarboxylate transport ; Sulfate transport ; Benzoyl compounds ; Phenoxy compounds ; Valproate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to study the specificity of the contraluminal para-aminohippurate (PAH) transport system, the inhibitory potency of monocarboxylates on the3H-PAH influx from the interstitium into cortical tubular cells in situ has been determined. The following was found: if a homologous series of fatty acids with increasing chain length is tested, inhibition of contraluminal PAH influx is first seen with valerate (app.K i 1.4 mmol/l), increasing up to nonanoate (app.K i 0.06 mmol/l) and remaining in this range up to duodecanoate, the last compound of this series which is sufficiently water-soluble. Similarly, the inhibitory potency of aromatic monocarboxylates increases with increasing hydrophobicity. If the fatty acids are esterified, their inhibitory potency is lost. If they are transformed to the respective aldehydes their inhibitory potency is preserved at a reduced degree. Introduction of a hydrophobic methyl-, ethyl-, or propyl-group increases the inhibitory potency. A β-, but not an α-oxo-group augments the inhibitory potency of phenylpropionate analogs, an OH group diminishes it, and a NH2 group abolishes it. Among phenyl-fatty acids an increase in affinity is observed from phenyl- 〈 benzoylamine-〈 phenoxy- 〈 benzoyl-acetate and-propionate. All monocarboxylate compounds, so far tested, do not inhibit contraluminal sulfate and Na+/succinate influx. The data indicate that the PAH transporter interacts with monocarboxylates and also with aldehydes which have a hydrophobic moiety. An additional oxo-group facilitates the interaction. Thus, the benzoyl compounds show the highest affinity observed.
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  • 2
    ISSN: 1432-2013
    Keywords: Renal tubule ; Sulfate transport ; Na+ coupled transport ; Thiosulfate ; Molybdate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Using the standing droplet technique in the proximal convolution and simultaneous microperfusion of the peritubular capillaries, the decrease in luminal sulfate concentration with time and the zero net flux transtubular concentration difference of sulfate ( $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ ) at 45 s was determined — the latter being taken as a measure of the rate of active sulfate reabsorption. Starting with 0.5 mmol/l sulfate in both perfusates the $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ value of 0.35 mmol/l was approached exponentially with a half value time of 4.3 s. The $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ values in the early proximal and late proximal convolution did not deviate from each other. If the Na+ concentration in the perfusates was reduced, the $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ approached zero and extrapolated to a slightly negative value (c i〉c o). When 1 mmol/l ouabain was added to the perfusates $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ decreased by 66% (the latter experiments were performed in the golden hamster which is more sensitive to ouabain than the rat). 1 mmol/l thiosulfate diminished $$\Delta c_{{\text{SO}}_{\text{4}}^{{\text{2 - }}} } $$ by 68% and 1 mmol/l molybdate by 24%. Omitting or replacing bicarbonate by HEPES or glycodiazine reduced the sulfate reabsorption significantly, while acetazolamide (0.1 mmol/l) and increasing the CO2-pressure from 4.66 to 14.0 kPa (i.e. 5–15% CO2) had no effect. SITS 1 mmol/l had no effect on sulfate reabsorption. The data indicate that the sulfate reabsorption is driven by a Na+ gradient and inhibited by thiosulfate and molybdate, i.e. molecules which have a similar tetrahedral molecule structure. The sulfate reabsorption depends in an undefined manner on the presence of bicarbonate ions.
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  • 3
    ISSN: 1432-2013
    Keywords: Organic anion transport ; Sulfate transport ; Dicarboxylate transport ; Phenolate transport ; Salicylate transport ; Cinnamate transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to study the specificities of the contraluminal anion transport systems, the inhibitory potency of substituted benzene analogs on influx of [3H]PAH, [14C]succinate, and [35S]sulfate from the interstitium into cortical tubular cells has been determined in situ: (1) Contraluminal [3H]PAH influx is moderately inhibited by benzene-carboxylate and benzene-sulfonate, and strongly by benzene-dicarboxylates,-disulfonates and carboxy-benzene-sulfonates, if the substituents are located at positions 1 and 3 or 1 and 4. The affinity of the PAH transporter to polysubstituted benzoates increases with increasing hydrophobicity, decreasing electron density at the carboxyl group and decreasing pKa. Similar dependencies are observed for phenols. Benzaldehydes which do not carry an ionic negative charge are accepted by the PAH-transporter, if they possess a second partially charged aldehyde or NO2-group. (2) Contraluminal [14C]succinate influx is inhibited by benzene 1,3- or 1,4-dicarboxylates,-disulfonates and 1,3-or 1,4-carboxybenzene-sulfonates. Monosubstituted benzoates do not interact with the dicarboxylate transporter, but NO2-polysubstituted benzoates do. Phenol itself and 2-substituted phenol interact weakly possibly due to oligomer formation. (3) The contraluminal sulfate transporter interacts only with compounds which show a negative group accumulation such as 3,5-dinitro- or 3,5-dichloro-substituted salicylates. The data are consistent with three separate anion transport systems in the contraluminal membrane: The PAH transporter interacts with hydrophobic molecules carrying one or two negative charges (−COO−, −SO 3 − ) or two or more than two partial negative charges (−OH, −CHO, −SO2NH2, −NO2). The dicarboxylate transporter requires two electronegative ionic charges (−COO−, −SO 3 − ) at 5–9 Å distance or one ionic and several partial charges (−Cl, −NO2) at a favourable distance. The sulfate transporter interacts with molecules which have neighbouring electronegative charge accumulation.
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  • 4
    ISSN: 1432-2013
    Keywords: Renal tubule ; Thiosulfate transport ; Na+ coupled transport ; Sulfate transport ; Paraaminohippurate transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Using the standing droplet method in the late proximal convolution and simultaneous microperfusion of the peritubular capillaries, the zero net flux transtubular concentration difference of thiosulfate at 45 s was determined, the latter being taken as a measure of active thiosulfate transport. Under control conditions, in the presence of Na+, near zero Δc values were observed. When 1 mmol/l carinamide or paraaminohippurate (PAH) were added to the perfusates significant reabsorptive Δc arose. However, when 7.5 mmol/l sulfate was added to the Na+-free secretory Δc values were observed. Tested under Na+-free conditions, the secretory Δc was not influenced by simultaneously present 5 mmol/l of SO 4 2− but was diminished by 50 mmol/l SO 4 2− . PAH (1 mmol/l), carinamide (0.2 mmol/l) and probenecid (1 mmol/l) decreased the secretory Δc by 48, 65 and 48%, respectively. The PAH secretion was not influenced, when thiosulfate or sulfate up to 50 mmol/l was added to both perfusates. Under Na+-free conditions the Δc of thiosulfate in early loops of the proximal convolution is higher than in late loops, while for PAH this pattern is reversed. Taken together with the previously published inhibition of sulfate reabsorption by thiosulfate the data indicate 1. thiosulfate is reabsorved by the Na+-dependent sulfate transport system and 2. thiosulfate is simultaneously secreted by a carinamide-, probenecid-and PAH-sensitive secretory system. The secretory system might also be shared by sulfate. The thiosulfate net flux is the result of the difference in the activity of the counteracting transporters, located at the luminal and contraluminal cell side. Is is possible that the higher activity of the transporter at one cell side leads to a reversal of the flux through the transporter at the other cell side.
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