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  • 1
    Electronic Resource
    Electronic Resource
    Active sulfate reabsorption in the proximal convolution of the rat kidney: Specificity, Na+ and HCO 3 − dependence (1980)
    Springer
    Pflügers Archiv 383 (1980), S. 159-163 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00581877
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  • 2
    Electronic Resource
    Electronic Resource
    Bidirectional active transport of thiosulfate in the proximal convolution of the rat kidney (1980)
    Springer
    Pflügers Archiv 387 (1980), S. 127-132 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584263
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Reabsorption of monocarboxylic acids in the proximal tubule of the rat kidney (1982)
    Springer
    Pflügers Archiv 395 (1982), S. 220-226 
    Details
    ISSN: 1432-2013
    Keywords: Na+-dependent transport ; d-Lactate transport ; Small fatty acids ; 3-Hydroxybutyrate ; Acetoacetate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The 3.5 s efflux ofd-lactate (1 mmol/l) injected in the lumen of the late proximal convolution as well as the zero net flux transtubular concentration difference ofd-lactate, which is a measure of its active transtubular transport rate, were determined. The inhibitory potency of small fatty acids and their analogs added to the perfusate in a concentration of 10 mmol/l on both, the 3.5 s efflux and in most cases also the 45 s transtubular concentration difference ofd-lactate was measured. It was found that 1. small fatty acids from acetate to octanoate inhibit 3.5s efflux ofd-lactate, the largest inhibition being exerted by propionate and butyrate. With increasing chain length the inhibitory potency decreased and disappeared with decanoate. 2. Considering the acetate-, propionate- and butyrate analogs, introduction of an electron attracting group such as Cl, Br, I, CN, SH, N3 on C atom 2 increased the inhibitory potency, compared to the unsubstituted fatty acid. An OH on C2 increased or did not change the inhibition while an OH on C atom 3 reduced or blunted the inhibition. A keto-group, as it is present in glyoxylate prevented inhibition, but pyruvate inhibited to the same extent as lactate, and acetoacetate was even more inhibitory than 3-hydroxybutyrate. Cl substitution on C3 preserved the strong inhibitory potency, while 4-Cl butyrate, was only sparsely inhibitory. A NH 3 + group at any position precludes inhibition. 3. As seen with Cl or OH substituted propionate and butyrate the inhibitory potency increased with decreasingpK a of the compounds. 4. Increasing the chain length by a CH3 as from acetate to propionate, from glycolate to lactate and also from glyoxylate to pyruvate increased the inhibitory potency. 5. When tested against the 3.5 s efflux ofl-lactate, the same inhibitory pattern was seen as withd-lactate. 6. The transport of chloroacetate, glycolate and acetoacetate, which were available in a radio-labeled form of high specific activity, was measured directly in 3.5 s efflux studies. It was Na+-dependent and could be inhibited by 10 mmol/ll-lactate. Glyoxylate, on the other hand, which did not inhibitd-lactate transport, did also not show a Na+-dependent,l-lactate inhibitable efflux from the tubular lumen. The data indicate that a variety of short chain fatty acids and their analogs are transported by the same Na+-dependent transport system in the brush border which transportsl- andd-lactate. The specificity is determined by the molecule size, hydrophobicity of one part of the molecule, the electron attracting abilities of substitutes on C-atom 2 or 3 and the charge distribution on the molecule.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584813
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    Paper (German National Licenses)
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