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• Renal tubule  (8)
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• 1
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Springer
Pflügers Archiv 360 (1975), S. 183-187
ISSN: 1432-2013
Keywords: Renal tubule ; Phosphate transport ; pH dependence ; Micropuncture ; Microperfusion
Source: Springer Online Journal Archives 1860-2000
Topics: Medicine
Notes: Summary Early loops of the proximal convoluted tubule of parathyroidectomized rats (PTX-rats) were microperfused with a phosphate (4 mM) containing perfusate. With a perfusion solution of pH around 7.45 as estimated as anion deficit theP i reabsorption was two times greater than with a perfusion solution of pH around 6.85. TheP i reabsorption is reduced in PTX-rats made chronic alkalotic (PTX-cA-rats) but the same pH dependence ofP i reabsorption was found. The data indicate that the divalent phosphate is preferentially reabsorbed.
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• 2
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Springer
Pflügers Archiv 368 (1977), S. 245-252
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.
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• 3
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Springer
Pflügers Archiv 372 (1977), S. 269-274
ISSN: 1432-2013
Keywords: Renal tubule ; Phosphate transport ; Parathyroidectomy ; Parathyroid hormone ; Phosphate diet
Source: Springer Online Journal Archives 1860-2000
Topics: Medicine
Notes: Summary The standing droplet method was applied in combination with microperfusion of the peritubular blood capillaries to determine the build up of transtubular concentration differences of phosphate (Pi) in proximal convoluted tubules. As revealed in experiments with chronic parathyroidectomized (PTX) rats, the time dependent decrease of the intraluminal Pi concentration, or increase of transtubular Pi concentration difference ( $$\Delta {\text{c}}_{{\text{P}}_i }$$ ), changes along the proximal convolution in a ratio 4:2:1 in the first quarter: second plus third quarter: fourth quarter. In acute (〉2 h) PTX rats $$\Delta {\text{c}}_{{\text{P}}_i }$$ decreased by 31% in the first and by 41% in the fourth quarter of the convolution when parathyroid hormone (PTH; 5 U initially and 12 U/h continuously) was infused. In chronic (〉2 days) PTX rats the correspondent values of 17% and 29% were significantly smaller. When the rats were kept for 7–11 weeks on a low phosphate diet (〈0,15% P in the dry matter) their Pi transport was in the range of that of the PTX rats. PTH infusion, however, diminished the P i reabsorption rate in the fourth quarter of the convolution only, but not that in the early parts of the convolution. On the contrary, rats kept for the same time on a high phosphate diet (2%) showed all along the proximal convolution one by one third of the phosphate transport rate of animals on a low phosphate diet. Acute parathyroidectomy of the high P diet rats led to 51% increase in P i transport. The data show that 1. the phosphate transport decreases as a function of proximal convolution length, 2. PTH exerts a considerable inhibitory effect on P i transport only in acute PTX rats, while the effect in chronic PTX rats is rather small, 3. the P content of the diet inversely correlates with the P i transport. 4. further with low P diet the PTH inhibits P i transport in late, but not in early segments of the proximal convolution.
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• 4
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Springer
Pflügers Archiv 375 (1978), S. 97-103
ISSN: 1432-2013
Keywords: Renal tubule ; Phosphate transport ; Paracellular shunt ; Calcium ; Ca2+ ionophore A 23187
Source: Springer Online Journal Archives 1860-2000
Topics: Medicine
Notes: Abstract Proximal inorganic phosphate (P i ) transport was evaluated using the standing droplet method with simultaneous microperfusion of the peritubular blood capillaries. In chronic parathyroidectomized (PTX) rats addition of 3 μM of the Ca2+ ionophore A 23187 to the luminal perfusate had no effect on the P i transport, although the isotonic fluid reabsorption was reduced by 20%. When the Ca2+ concentration in the perfusates was raised from 1.5 mM to 3.0 mM the reabsorption did not change significantly. But when Ca2+ was omitted from the perfusates the P i reabsorption dropped by 19%, and when 2 mM EDTA were added to the perfusates P i transport decreased by 35%. The influx of P i from the interstitial space and from the cell into the phosphate-free luminal perfusate did not change, when the perfusates were Ca2+-free, but it increased by 23% in the presence of 2 mM EDTA. The data indicate that 1. a rise in intracellular Ca2+ above normal is not a factor which modifies “basal” P i transport i.e. when P i transport is independent of the action of parathyroid hormone. 2. A reduction of extracellular Ca2+ concentration from normal toward zero reduces P i transport without changing the paracellular leak permeability for P i . 3. With EDTA the paracellular leak permeability for P i is increased, thus causing an even greater reduction in net P i transport than with Ca2+-free solutions alone.
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• 5
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Springer
Pflügers Archiv 383 (1980), S. 159-163
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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• 6
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Springer
Pflügers Archiv 395 (1982), S. 212-219
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 .
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• 7
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Springer
Pflügers Archiv 387 (1980), S. 127-132
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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• 8
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Pflügers Archiv 377 (1978), S. 33-42
ISSN: 1432-2013
Keywords: Renal tubule ; Phosphate transport ; Extracellular pH ; Intracellular pH ; Acetazolamide
Source: Springer Online Journal Archives 1860-2000
Topics: Medicine
Notes: Abstract Inorganic phosphate (Pi) transport was evaluated using the standing droplet method with simultaneous microperfusion of the peritubular capillaries. To evaluate rather small differences in Pi transport and to eliminate the influence of tubular heterogeneity, the technique of crossed paired samples was applied. 1. In chronic PTX rat changing the luminal or both luminal and peritubular pH by varying the HCO 3 − -concentration between 4 and 50 mmol/l at constant 5% CO2 had no influence on Pi transport. 2. If, however, bicarbonate was omitted from the perfusate and 2 mmol/l phosphate (pH 7.4) was the only buffer, Pi transport was decreased from the control. It was, however, further reduced when the perfusates were gased with 5% CO2 i. e. the starting pH was 5.6. 3. When the solutions contained HEPES buffer (25 mmol/l), Pi transport at pH 8 was much larger than at pH 6.0. 4. Raising the CO2 pressure from 35 to 70 mm Hg did not change the Pi transport when both perfusates had a HCO 3 − -concentration of 25 mmol/l. It reduced, however, the Pi transport, when the luminal perfusate had only 4 mmol/l bicarbonate. 5. Lowering the CO2 pressure from 38 to 7.6 mm Hg did hardly change the Pi transport when the luminal perfusate contained 4 mmol/l bicarbonate. It lowered, however, the Pi transport significantly when the luminal perfusate had 25 mmol/l bicarbonate. 6. Acetazolamide, 10−4 M, lowered the Pi transport when the luminal perfusate contained 4 or 25 mmol/l bicarbonate. At 4 mmol/l luminal HCO 3 − , raising thepCO2 to 228 mmol/l depressed Pi transport even more. At 25 mmol/l luminal bicarbonate, raising thepCO2 from 38 to 114 mm Hg reversed the acetazolamide inhibition of the Pi transport almost completely. The data indicate that luminal acidosis and intracellular alkalosis inhibits the transtubular Pi transport. A shift of the intracellular pH to a more alkaline value seems to be responsible for the inhibition of Pi transport by acetazolamide, while omission of buffer from the perfusate inhibits Pi transport by effecting an acidic luminal pH.
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