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  • 1
    Electronic Resource
    Electronic Resource
    Bicarbonate reabsorption in the papillary collecting duct of rats (1981)
    Springer
    Pflügers Archiv 389 (1981), S. 271-275 
    Details
    ISSN: 1432-2013
    Keywords: Adaptation, HCO 3 − transport ; Glycodiazine transport ; Metabolic acidosis ; Metabolic alkalosis ; Acetazolamide ; SITS ; Potassium deficiency
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Using the technique of capillary perfusion and simultaneous luminal stop flow microperfusion the reabsorption of bicarbonate and glycodiazine from the papillary collecting duct was evaluated. Starting with equal H14CO 3 − and3H-glycodiazine concentrations in the luminal and peritubular perfusates, the decrease in the luminal concentration at 10 and 45 s contact time was measured. In control rats with 25 mmol/l HCO 3 − in the perfusates the rate of HCO 3 − reabsorption calculated from the 10 s values was 0.34 nmol cm−2s−1. In acute metabolic acidosis, the rate of bicarbonate reabsorption was 2,3 times higher. In metabolic alkalosis, the rate of bicarbonate absorption dropped to 13% of the control values. Also the 45 s values of acidotic and alkalotic animals differed significantly from each other. With 25 mmol/l glycodiazine in both perfusates the rate of biffer reabsorption as calculated from the 10 s values was 0.76 nmol cm−2s−1 in control rats and did not deviate significantly from this value in acidotic and alkalotic animals. In control rats the bicarbonate reabsorption in % was the same, no matter whether both luminal and capillary perfusate contained 25 mmol/l bicarbonate or 10 mmol/l. In acidotic rats the rate of HCO 3 − reabsorption did not change significantly if all Na+ in the perfusates was replaced by choline (0.88 versus 0.79 nmol cm−2s−1 at 25 mmol/l HCO 3 − ). When in acidotic rats 0.1 mmol/l acetazolamide or 1 mmol/l SITS (4-acetamido-4′-isothiocyanatostilbene-2,2′-disulfonic acid) was added to both perfusates the rate of HCO 3 − reabsorption dropped by 75 and 58%, respectively. A potassium deficient diet for one week and DOCA administration had no influence on the bicarbonate reabsorption of rats which were on standard diet. The data indicate that (1) the buffer reabsorption from the papillary collecting duct is rather due to H+ ion secretion than to buffer anion reabsorption. (2) The adaptation to metabolic acidosis and alkalosis is specific for bicarbonate and not seen with glycodiazine. (3) Within the concentration range tested the HCO 3 − reabsorption rises linearly with the HCO 3 t- concentration. (4) The HCO 3 − reabsorption in the papillary collecting duct is Na+-independent, it can be inhibited by acetazolamide and SITS, but is not influenced by K+-deficient diet plus DOCA.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584789
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  • 2
    Electronic Resource
    Electronic Resource
    Contraluminal transport of small aliphatic carboxylates in the proximal tubule of the rat kidney in situ (1986)
    Springer
    Pflügers Archiv 407 (1986), S. 488-492 
    Details
    ISSN: 1432-2013
    Keywords: Lactate ; Pyruvate ; 3-hydroxybutyrate ; Acetoacetate ; Nonspecific anion channel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to study the characteristic of contraluminal transport of hydrophylic small fatty acids the in situ stopped flow microperfusion technique [12] has been applied. By measuring with 4 s contact time the decrease in the contraluminal concentration of the respective radiolabelled substances the concentration dependence of the influx into the cortical cells was tested. The 4 s decrease in contraluminal concentration of chloroacetate,l-lactate,d-lactate, 3-hydroxybutyrate and acetoacetate was between 26% and 31%. For each substance the percent decrease was the same, no matter whether it was offered in a concentration of 0.1 or 10 mmol/l. Contraluminal disappearance of 0.1 mmol/ll-lactate was not influenced by 5 mmol/l H2DIDS, probenecid, phloretin, mersalyl or cyanocinnamate, but it was significantly (37%) inhibited by 5-nitro-2-(phenyl-propyl-amino) benzoate, a blocker of the nonspecific anion channel. The percent decrease in propionate uptake was somewhat larger — between 36% and 39% — but again not different at 0.01, 0.1, 1.0 and 10 mmol/l. With pyruvate the contraluminal decrease was 20% at 0.1 mmol/l and 31% at 10 mmol/l. The percent disappearance of the aromatic pyrazinoate was 38% and 34% at 0.1 and 10 mmol/l and for nicotinate 42% and 22%, respectively. The disappearance of nicotinate (0.1 mmol/l) was significantly inhibited by 10 mmol/l pyrazinoate and paraaminohippurate (PAH). The data are in agreement with the hypothesis that the hydrophilic small fatty acids traverse the contraluminal cell side by simple diffusion, possibly via the unspecific anion channel [14], pyruvate via the dicarboxylic acid pathway in a cooperative manner and pyrazinoate, as well as nicotinate, via the PAH pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00657505
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  • 3
    Electronic Resource
    Electronic Resource
    Coupling between proximal tubular transport processes (1977)
    Springer
    Pflügers Archiv 368 (1977), S. 245-252 
    Details
    ISSN: 1432-2013
    Keywords: Renal tubule ; H+ ion secretion ; Na+ coupled transport ; Ouabain ; SITS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The rate of active transport by the proximal renal tubule of amino acid (l-histidine), sugar (α-methyl-d-glycoside), H+ ions (glycodiazine), phosphate and para-aminohippurate was evaluated by measuring the zero net flux concentration difference (Δc) of these substances. In the case of calcium the electrochemical potential differenceΔc +zFci Δϕ/RT) was the criterion employed. The rate of isotonic Na+-absorption (JNa) was measured with the shrinking droplet method. The effect of ouabain on the transport of these substances was tested in the golden hamster and the effect of SITS (4-acetamido-4′isothiocyanatostilbene 2,2′-disulfonic acid) was observed in rats. Ouabain (1 mM) applied peritubularly incompletely inhibited JNa (80%), but in combination with acetazolamide (0.2 mM) the inhibition was almost complete (93%). In addition, ouabain inhibited the sodium coupled (secondary active) transport processes ofl-histidine, α-methyl-d-glycoside, calcium and phosphate by more than 75%. It did not affect H+ (glycodiazine) transport and PAH transport was only slightly affected. When SITS (1 mM) was applied from both sides of the cell it inhibited H+ (glycodiazine) transport by 72% and reduced JNa by 38% when given from only the peritubular cell side. SITS (1 mM), however, had no significant affect on H+ secretion and sodium reabsorption if it was applied from only the luminal side. Furthermore it had no affect on the other transport processes tested, regardless of the cell side to which it was applied. When the HCO 3 − buffer or physically related buffers were omitted from the perfusate the absorption of Na+ was reduced by 66%, phosphate by 44%, andl-histidine by 15%. All the other transport processes tested were not significantly affected. The data are consistent with the hypothesis that the active transport processes of histidine, α-methyl-d-glycoside and phosphate, which are located in the brush border, are driven by a sodium gradient which is abolished by ouabain. This may also apply to the Na+-Ca2+ countertransport located at the contraluminal cell side. The residual Na+ transport remaining in the presence of ouabain is likely to be passively driven by the continuing H+ transport which probably is driven directly by ATP. SITS seems to inhibit the exit step of HCO 3 − from the cell and secondary to that, the luminal H+-Na+ exchange and consequently the Na+ reabsorption. In the absence of HCO 3 − buffer in the perfusates the luminal H+-Na+ exchange seems to be affected and the pattern of inhibition of the other transport processes is almost the same as with SITS. The different effects onP i reabsorption observed under these conditions might be explained by possible variations in intracellular pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585203
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  • 4
    Electronic Resource
    Electronic Resource
    Reabsorption of monocarboxylic acids in the proximal tubule of the rat kidney (1982)
    Springer
    Pflügers Archiv 395 (1982), S. 212-219 
    Details
    ISSN: 1432-2013
    Keywords: SITS ; Probenecid ; Phloretin ; Acetazolamide ; Lactate ; Renal tubule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The transport ofd-lactate across the epithelium of the late proximal convolution was investigated by two methods: 1. by measuring the zero net flux transtubular concentration difference (Δc tt,45s) and the permeability (P) ofd-lactate and calculating from both the transtubular active transport rate (J lac act ). 2. By measuring the 3.5 s efflux ofd-lactate from the tubular lumen, while blood was flowing through the capillaries. The 3.5 s efflux comprises two components, one going through the brush border (J lac bb ) and one going the paracellular pathway (J lac paracell =P lac·c lac lumen). Both,J lac act andJ lac bb ofd-lactate gave the sameK m 1.9 and 1.7 mmol/l and the same maximal transport rate 3.2 and 2.9 pmol cm−1 s−1. TheK i ofl-lactate tested againstJ lac act andJ lac bb ofd-lactate was also the same: 1.1 and 1.0 mmol/l. These data indicate that under our experimental conditions only the flux through the brush border seems to be rate limiting and thatd-lactate uses the same transport system asl-lactate. When Na+ was omitted from the perfusatesJ lac act disappeared completely, whileJ lac bb was reduced by 64%. These data reflect the Na+ dependence of thed-lactate transport through the brush border. Variation of intra-and extracellular pH by raisingpCO2, omitting HCO 3 − from the perfusates or adding acetazolamide had no effect on the transport ofd-lactate when α-ketoglutarate was used as fuel. However, when acetate was used as fuel, intracellular acidosis brought the reducedJ lac act back to the values obtained with α-ketoglutarate as fuel. It is suggested that this is an effect on a contraluminal transport step. Probenecid (5 mmol/l) and phloretin (0.25 mmol/l) inhibitedJ lac act significantly.J lac bb , however, was only inhibited by probenecid when acetate was used as fuel. These data indicate that both compounds act on thed-lactate exit at the contraluminal cell side, but that probenecid acts in addition at the luminal cell side. SITS (1 mmol/l) augmentedJ lac bb when acetate was used as fuel and is similar to the effect of lowering intracellular pH as described above. The SH reagents mersalyl (1.0 mmol/l) and maleolylglycine (1 mmol/l) did not influenceJ lac bb .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584812
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  • 5
    Electronic Resource
    Electronic Resource
    Einfluß von Calciumionen und antidiuretischem Hormon auf den transtubulären Natriumtransport in der Rattenniere (1969)
    Springer
    Pflügers Archiv 310 (1969), S. 369-376 
    Details
    ISSN: 1432-2013
    Keywords: Nephron ; Sodium Transport ; Calcium Ions ; Antidiuretic Hormone ; Nierentubuli ; Natriumtransport ; Calciumionen ; Antidiuretisches Hormon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung An proximalen Tubuli und medullären Sammelrohren von Ratten wurde der isotone Natriumtransport ΆNa iso und die Gleichgewichtskonzentrationsdifferenz Δc Na bei Nettosubstanzfluß und Nettovolumenfluß Null gemessen. Die peritubulären Capillaren waren bei diesen Messungen künstlich durchströmt, und zwar in der ersten Serie mit einer Calcium-freien Lösung bzw. einer Lösung, die 3 mÄq Ca++/l enthielt, in einer zweiten Serie mit einer Lösung, die kein ADH bzw. 5 mE/l ADH enthielt. Zugabe von ADH oder Weglassen von Calcium aus dem Perfusat hatten keinen Einfluß auf den isotonen Natriumtransport. Die Natrium-Gleichgewichtskonzentration bei Nettosubstanzfluß Null war jedoch stark erniedrigt. Die Befunde sprechen dafür, daß bei Fehlen von Calcium oder Zugabe von ADH die Permeabilität für Natriumionen erhöht ist, daß aber im Gegensatz zum Verhalten von Amphibienhäuten der aktive Natriumtransport unbeeinflußt bleibt.
    Notes: Summary Isotonic sodium transport, ΆNa iso, and the transtubular concentration difference, Δc Na, at equilibrium under conditions of zero net solvent and solute fluxes were measured in the proximal tubules and medullary collecting ducts of rats. Peritubular capillaries were simultaneously perfused, in the first group of experiments with a solution containing no Ca++ or 3 mEq/l of Ca++, and in the second group with a solution which contained either no ADH or 5 mU/l of ADH. Addition of ADH or omission of Ca++ from the capillary perfusate did not affect isotonic sodium transport. The equilibrium concentration difference of sodium, Δc Na, was, however, greatly reduced under the same conditions. The results indicate that in the absence of Ca++, or in the presence of ADH, the permeability for sodium is increased, but that in contradistinction to the behaviour of amphibian skins, active sodium transport remains unaffected.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587245
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  • 6
    Electronic Resource
    Electronic Resource
    Einfluß von Aldosteron auf den Natriumtransport in den Sammelrohren der Säugetierniere (1969)
    Springer
    Pflügers Archiv 308 (1969), S. 111-126 
    Details
    ISSN: 1432-2013
    Keywords: Micropuncture ; Functional Isolated Collecting Ducts ; Sodium Transport ; Sodium Permeability ; Aldosterone ; Mikropunktion ; funktionell isoliertes Sammelrohr ; Natriumtransport ; Natriumpermeabilität ; Aldosteron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Durch Mikropunktion und -perfusion der Vasa recta an der freigelegten Nierenpapille von Wistarratten wurde es möglich, die schwankenden Harnstoff- und Natriumkonzentrationen im Interstitium des Nierenmarks zu beseitigen und definierte Versuchsbedingungen für die Sammelrohre zu schaffen. An diesen „funktionell” isolierten Sammelrohrabschnitten wurdenin situ sowohl die Gleichgewichtskonzentrationsdifferenz bei fehlendem Nettosubstanz-und -volumenfluß (ΔC Na) als auch der Nettonatriumtransport (Φ Na) bei gleicher Natriumkonzentration auf beiden Seiten der Sammelrohrwand gemessen. Es konnte gezeigt werden, daß unter diesen Versuchsbedingungen, bei denen die Tiere in Antidiurese sind, die Natriumrückresorption aus den Sammelrohren isoton abläuft. Die Versuche wurden an vier Tiergruppen durchgeführt: an adrenalektomierten Tieren, an normal ernährten Tieren, an salzarm ernährten Tieren und an normal ernährten Tieren, die zusätzlich Aldosteron bekamen. Φ Na iso war bei adrenalektomierten Tieren 1,2·10−5 bei normal ernährten Tieren 3,1·10−5, bei salzarm ernährten Tieren 4,1·10−5 und bei normal ernährten Tieren unter Aldosteronsubstitution 4,2·10−5 μÄq·mm−2·sec−1. Die entsprechenden ΔC Na werte waren 4, 31, 98, 93 mÄq/l. Unter der Annahme, daßΦ Na iso die Transportkapazität des Systems angibt und daß ΔC Na bei gegebenemΦ Na iso umgekehrt proportional der Leckpermeabilität für Natriumionen ist, kann man aus den vorliegenden Daten schließen, daß Aldosteron am Sammelrohr nicht nur die innere Transportkapazität für Na erhöht, sondern auch die Leckpermeabilität für Na herabsetzt.
    Notes: Summary Micropuncture and -perfusion were performed on vasa recta of the exposed renal papilla in Wistar rats in order to abolish uncontrollable changes of sodium and urea concentration within the medullary interstitium. Thereby the collecting tubules could be studied under well defined experimental conditions. The transport of sodium in the absence of a transtubular concentration difference (Φ Na) as well as differences in steady state concentration of sodium (ΔC Na) at zero net flux of water and solutes were measuredin situ in these functionally isolated collecting ducts. Four groups of animals were studied: adrenalectomized rats, control rats on a normal diet, rats on low sodium diet and normally fed rats with additional aldosterone administration. The respectiveΦ Na were 1.2, 3.1, 4.1 and 4.2·10−5 μeq×mm−2×sec−1, while ΔC Na were 4, 31, 98 and 93 meq/l. One may assume thatΦ Na iso is a measure of the transport capacity of the system and that ΔC Na at a givenΦ Na iso is inversely proportional the leak permeability. Under these conditions our data suggest, that aldosterone causes an increase of intrinsic transport capacity and at the same time a decrease of leak permeability for sodium ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587019
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  • 7
    Electronic Resource
    Electronic Resource
    Natriumtransport in den proximalen Tubuli und den Sammelrohren bei Variation der Natriumkonzentration im umgebenden Intterstitium (1969)
    Springer
    Pflügers Archiv 310 (1969), S. 354-368 
    Details
    ISSN: 1432-2013
    Keywords: Perfusion of Peritubular Capillaries ; Water Reabsorption ; Sodium Transport ; Proximal Convolution ; Collecting Duct ; peritubuläre Capillarperfusion ; Wasserresorption ; Natriumtransport ; proximales Konvolut ; Sammelrohre
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung An Ratten wurden Mikropunktionsuntersuchungen am proximalen Tubulus und am Sammelrohr bei Durchblutung der peritubulären Capillaren bzw. Vasa recta sowie bei künstlicher Perfusion dieser Blutgefäße durchgeführt. In Abhängigkeit von der Höhe der interstitiellen Natriumkonzentration wurden der Nettonatriumtransport (ΆNa iso) bei gleicher Natriumkonzentration zu beiden Seiten der Tubuluswand und die Gleichgewichtskonzentrationsdifferenz (Δc Na) bei fehlendem Nettovolumen- und Nettosubstanzfluß gemessen. Bei Variation der Natriumkonzentration im Gewebe durch Perfusion der peritubulären Capillaren mit 155 bzw. 300 mÄq/l Na änderten sich weder ΆNa iso noch Δc Na für den proximalen Tubulus (ΆNa iso 8,4 bzw. 7,9·10−5 μÄq · mm−2 · sec−1; Δc Na 24 bzw. 24 mÄq/l). Veränderung der Natriumkonzentration im Blut durch Infusion hypertoner NaCl Lösung oder Peritonealdialyse mit isotoner Mannitlösung führten zu prinzipiell gleichen Ergebnissen. Bei Perfusion der Vasa recta mit Lösungen, die 145 und 300 mÄq/l Natrium entheilten, blieben ΆNa iso wie Δc Na über die Sammelrohrwand ebenfalls konstant (ΆNa iso 4,1 bzw. 4,1·10−5 μÄq · mm−2 · sec−1; Δc Na 98 bzw. 104 mÄq/l). Proximale Tubuli und Sammelrohre verhalten sich demnach bei Variation der interstitiellen Natriumkonzentration gleich. Da die Wasserresorption aus den Sammelrohren von dem durch Gegenstrommultiplikation erzeugten Natriumkonzentrationsanstieg im Markinterstitium abhängt, die Natriumresorption aus den Sammelrohren aber wie die vorliegenden Befunde zeigen von eben dieser Natriumkonzentration unabhängig ist, ist dem Warmblüterorganismus die Möglichkeit gegeben, Natrium- und Wasserresorption unabhängig voneinander zu variieren. Die Natrium- und Wasserresorption aus den Sammelrohren werden jedoch beide durch den Gehalt der Sammelrohrflüssigkeit an permeablen Nichtelektrolyten, wie z. B. Harnstoff, beeinflußt.
    Notes: Summary Micropuncture experiments were performed on proximal tubules and collecting ducts of rat kidneys with and without artificial perfusion of surrounding capillaries or vasa recta respectively. Net sodium flux (ΆNa iso) was estimated under conditions of varying but equal sodium concentrations on both sides of the tubular wall. The transtubular wall equilibrium concentration difference of sodium (Δc Na) was also measured in these nephron segments under conditions of zero volume and solute fluxes. In the proximal tubule ΆNa iso of 8.4 and 7.9×10−5 μeq × mm−2 × sec−1 at sodium concentrations of 155 and 300 meq/l in the perfusion fluid and Δc Na of 24 and 24 meq/l respectively did not vary significantly. Variations of sodium concentrations in blood produced by hypertonic saline infusion or peritoneal dialysis with mannitol resulted in essentially similar values of ΆNa iso and Δc Na. In the collecting ducts also ΆNa iso and Δc Na remained uninfluenced by induced variations in sodium concentrations of the perfusion fluid. ΆNa iso at sodium concentration of 145 and 300 meq/l in the perfusion fluid of vasa recta was 4.1 and 4.1×10−5 μeq × mm−2 × sec−1 respectively and Δc Na was 98 and 104 meq/l respectively. Water reabsorption in the collecting ducts depends on the increase of sodium concentration produced in the medulla by the countercurrent multiplier system. The results represented here indicate that, in mammals sodium reabsorption is independent from the sodium concentration of the interstitial fluid. Therefore the sodium reabsorption and the water reabsorption can be varied independently from each other. Both, sodium and water reabsorption in the collecting ducts are however dependent upon the concentrations of permeable nonelectrolytes such as urea in the collecting duct fluid.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587244
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  • 8
    Electronic Resource
    Electronic Resource
    Einfluß von Aldosteron auf den Ausstrom markierten Natriums aus den Sammelrohren der Ratte (1970)
    Springer
    Pflügers Archiv 320 (1970), S. 261-264 
    Details
    ISSN: 1432-2013
    Keywords: Micropuncture ; Collecting Duct ; Sodium Transport ; Sodium Permeability ; Aldosterone ; Schlüsselwörter ; Mikropunktion ; Sammelrohr ; Natriumtransport ; Natriumpermeabilität ; Aldosteron
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In previous micropuncture studies with collecting ducts from the rat kidney, aldosterone was shown to increase the isotonic sodium reabsorption as well as the transepithelial concentration difference for sodium under steady state conditions with zero net flux. It was thought that the latter effect might have been partially due to a reduced leak permeability for sodium caused by the action of the hormone. To examine this possibility, the24Na efflux from the collecting duct was studied and found to be decreased by aldosterone. It follows that the hormone must cause a substantial decrease in sodium permeability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587457
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  • 9
    Electronic Resource
    Electronic Resource
    Contraluminal para-aminohippurate (PAH) transport in the proximal tubule of the rat kidney (1987)
    Springer
    Pflügers Archiv 409 (1987), S. 229-235 
    Details
    ISSN: 1432-2013
    Keywords: 2-Oxoglutarate ; Lactate ; Pyruvate ; Nitrate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to study the characteristics of contraluminal para-aminohippurate transport into proximal tubular cells the stopped flow capillary perfusion method was applied. The disappearance of3H-paraaminohippurate from the capillary perfusate at different concentrations and contact times was measured and saturation type behaviour was found with aK m of 0.08±0.01 (SE) mmol/l,J max of 1.1±0.1 pmol·s−1·cm−1 andr, the final extracellular/intracellular distribution ratio of 0.93±0.03. Omission of Na+ from the capillary test perfusate caused a small reduction of contraluminal PAH uptake at small transport rates (0.1 mmol/l PAH in the test perfusate) but not at high transport rates (1.0 mmol/l PAH in the test perfusate). Change of K+ between 0 and 40 mmol/l and pH between 6.0 and 8.0 did not influence contraluminal PAH uptake. Isotonic replacement of chloride by gluconate, nitrate, sulfate, phosphate, methanesulfonate or increase in bicarbonate to 50 mmol/l did not influence PAH uptake at small transport rates. But isotonic sulfate and phosphate, as well as 50 mmol/l HCO 3 − and 25 mmol/l Hepes in isotonic solutions reduced PAH uptake at high transport rates. Addition of 5 mmol/l Ca2+, Mg2+, Mn2+, Ba2+, Cd2+ to isotonic Na+-gluconate solution did not influence PAH uptake except for Mg2+ and Mn2+ which inhibited uptake at small transport rates only. Preperfusion of the peritubular capillaries with rat serum, Na+ gluconate (Ca2+-+Mg2+-free), Na+ gluconate (Ca2+-+Mg2+-free) plus 10 mmol/l lactate or pyruvate or 0.1 mmol/l 2-oxoglutarate did not influence PAH uptake at small PAH transport rates, but inhibited at high transport rates. Preperfusion of the capillaries for 10 s with Na+-, Ca2+- and Mg2+-free solutions reduced PAH uptake in the presence of Na+ at both transport rates. A second 10 s preperfusion — after the first 10 s Na+-, Ca2+-, Mg2+-free preperfusion — with serum or solutions which contained Na+ and Ca2+ or Mg2+ restored the PAH fluxes to control values. The data are compatible with the hypothesis that contraluminal PAH uptake occurs by a saturable transport mechanism in exchange for other intracellular anions rather than in cotransport with Na+ ions. It was, however, not possible to identify the type of counteranions involved. The large effect of cation replacement on para-aminohippurate transport, which was reported in many previous studies with kidney slices, is not a direct effect on the para-aminohippurate transporter, but is rather caused indirectly via cell metabolism and/or changed ion gradients.
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    URL: http://dx.doi.org/10.1007/BF00583470
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