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  • Micropuncture  (7)
  • 1
    Electronic Resource
    Electronic Resource
    Urate handling by the rat kidney (1974)
    Springer
    Pflügers Archiv 352 (1974), S. 115-120 
    Details
    ISSN: 1432-2013
    Keywords: Urate ; Reabsorption ; Loop of Henle ; Micropuncture ; Microperfusion ; Microinjection ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Reabsorption rates for urate in the loops of Henle were measured in superficial nephrons in the rat 1. under conditions of free flow, 2. using microperfusion and 3. by a microinjection technique. 1. Under conditions of free flow distally measured TF/PUA/TF/PIn-values varied between 0.51 and 0.38 in antidiuretic rats, depending on TF/PIn (UA = both uric acid and urate, In = inulin, TF/P = concentration in tubular fluid to plasma concentration). The corresponding values in samples from end-proximal tubules were 1.06 and in urine 0.19 (U/PUA/U/PIn). 2. In microperfusion experiments of Henle loops early distal recoveries of 2-C14 urate varied between 57 and 86%, depending on the flow rates (10–40 nl/min). 3. In microinjection experiments C14 recovery in urine was about 85% when tracer solution was microinjected into endproximal tubules. From these results we conclude: 1. The main site of urate reabsorption is located in the loops of Henle. 2. This reabsorption is highly dependent on flow rates. Increase of flow rate through Henle's loop decreases urate reabsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587510
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  • 2
    Electronic Resource
    Electronic Resource
    Na+ and Cl− conductances in airway epithelial cells: increased Na+ conductance in cystic fibrosis (1995)
    Springer
    Pflügers Archiv 431 (1995), S. 1-9 
    Details
    ISSN: 1432-2013
    Keywords: Na+ channel ; Respiratory epithelial cells ; Human Na+ channel ; Micropuncture ; Patch clamp ; Cystic fibrosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Na+ and Cl− conductances in the apical membrane of respiratory epithelial cells are essential for electrolyte and water transport in the airways. Apart from the well described defect in adenosine 3′∶5′ cyclic monophosphate-(cAMP-) dependent activation of Cl− conductances in cystic fibrosis (CF), an increased Na+ conductance has also been reported from transepithelial measurements. In the present experiments we tried to identify these conductances in nasal epithelial cells using patch-clamp and microelectrode techniques. With these methods we found identical and relatively low membrane voltages of about −36 mV in both freshly isolated and primary cultured normal and CF nasal epithelial cells. A Cl− conductance could be activated by cAMP in normal (ΔG=3.1±0.8 nS, n=10) but not in CF (ΔG=0.3±0.1 nS, n=11) cells, whereas Ca2+-dependent Cl− currents activated by adenosine 5′-triphosphate (ATP) and bradykinin were present in both types of cells. Cell-attached membrane patches from stimulated cells did not reveal discernible singlechannel events when activated with any of the agonists. A Na+ conductance was also detected in freshly isolated ciliated respiratory cells in impalement studies, as evidenced by the hyperpolarization induced by 10 μmol/l amiloride (ΔV= −5.2±0.6 mV, n=56) and when Na+ was replaced in the bath by N-methyld-glucamine (NMDG) (ΔV = −5.7±0.9 mV, n=14). In whole-cell patch-clamp experiments, the amilorideinduced hyperpolarization was significantly larger in CF (ΔV = −9.7±2.4 mV, n=22) when compared to normal (ΔV = −3.3±0.9 mV, n=27) cells in short-term culture. Reverse transcriptase polymerase chain reaction analysis of normal respiratory cells identified messenger RNA of both the cystic fibrosis transmembrane conductance regulator (CFTR) as well as the human epithelial Na+ channel (hNaCh). The present experiments confirm the absence of a cAMP-dependent Cl− conductance in CF respiratory epithelial cells and support previous findings obtained in transepithelial and microelectrode studies which indicate an increased Na+ conductance in respiratory epithelial cells from CF patients.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374371
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  • 3
    Electronic Resource
    Electronic Resource
    Handling of uric acid by the rat kidney (1971)
    Springer
    Pflügers Archiv 324 (1971), S. 279-287 
    Details
    ISSN: 1432-2013
    Keywords: Uric Acid Secretion ; Micropuncture ; Renal Tubule ; Ultramicro Analysis ; Harnsäuresekretion ; Mikropunktion ; Nierentubulus ; Ultramikroanalyse
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Mit Hilfe der Mikropunktionstechnik und einer neu entwickelten Methode der Ultramikroanalyse wurde der Harnsäuretransport am proximalen Tubulus der Rattenniere untersucht. Unter normalen Bedingungen ohne Harnsäureinfusion und ohne osmotische Diurese konnte eine Harnsäure-Netto-Sekretion im proximalen Tubulus nachgewiesen werden. Dabei war in diesen Experimenten die Inulinclearance etwa doppelt so groß wie die Harnsäureclearance. In der Bilanz wurde also mehr Harnsäure resorbiert als sezerniert, aber nicht, wie früher angenommen, im proximalen Tubulus.
    Notes: Summary Uric acid transport in the rat proximal tubule was studied by micropuncture and a new method of chemical ultramicro analysis. Under normal free-flow conditions at physiological levels of uric acid plasma concentrations a net secretion of uric acid in the proximal tubule was demonstrated. In these experiments the clearance ratio of uric acid to inulin was in the range of 0.4 which is normal in antidiuretic rats. Net reabsorption of uric acid, therefore, took place in the kidney, but certainly not in the proximal tubule as previously suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00592456
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  • 4
    Electronic Resource
    Electronic Resource
    Handling of allantoin by the rat kidney (1975)
    Springer
    Pflügers Archiv 357 (1975), S. 201-207 
    Details
    ISSN: 1432-2013
    Keywords: Allantoin ; Uricase ; Kidney ; Clearance ; Micropuncture ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Renal excretion of allantoin was measured by tracer techniques. After injection of 2-C14 urate and H3 inulin, clearances of allantoin and inulin were measured and both proximal and distal tubules were micropunctured. In confirmation of earlier results 2-C14 urate injected into an intact animal is very rapidly converted to C14 allantoin: after 15 min more than 90% of urinary tracer is present as allantoin. It was further observed that 1) allantoin clearance is essentially identical with inulin clearance over a wide range of urine flows; 2) no net transport of allantoin occurs in either proximal or distal tubules. Clearly allantoin is handled by the rat kidney like inulin. The total excretion of filtered allantoin unlike that of filtered urate provides an easy and effective mechanism for animals possessing the enzyme uricase to dispose of their purine loads.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00585975
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of benzolamide on luminal pH in proximal convoluted tubules of the rat kidney (1978)
    Springer
    Pflügers Archiv 375 (1978), S. 39-43 
    Details
    ISSN: 1432-2013
    Keywords: Proximal tubule ; Micropuncture ; Carbonic anhydrase ; Benzolamide ; Acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Luminal pH in early and late proximal tubules was recorded continuously with antimony microelectrodes before and during carbonic anhydrase inhibition. Following i.v. application of benzolamide (25 μmol/kg BW), luminal pH decreased almost immediately in early proximal tubules (ΔpH −0.42±0.06 SEM), but increased in late proximal tubules (ΔpH +0.27±0.06). Urinary pH increased (ΔpH +1.6±0.16) after a delay of some 30 s. Similar results, i.e. decrease of pH in early and increase of pH in late proximal tubules, were obtained, when benzolamide containing solutions were microinfused into early proximal tubules or superfused on the nephron surface. In contrast, luminal pH decreased in late proximal tubules, when benzolamide was microinfused into the same nephron segment. The decrease of luminal pH indicates inhibition of luminally active carbonic anhydrase, leading to delayed buffering of secreted hydrogen ions. The increase of luminal pH in late proximal tubules may be attributed to several factors including increased delivery of bicarbonate, impaired bicarbonate exit at the antiluminal membrane and decreased hydrogen ion formation in the tubular cell due to inhibition of cellular carbonic anhydrase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584146
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  • 6
    Electronic Resource
    Electronic Resource
    Carbonic anhydrase independent bicarbonate reabsorption (1982)
    Springer
    Pflügers Archiv 395 (1982), S. 121-125 
    Details
    ISSN: 1432-2013
    Keywords: Bicarbonate ; Renal tubular transport ; Carbonic anhydrase inhibition ; Permeability ; Microperfusion ; Micropuncture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The present study was designed to define the prerequisites of carbonic anhydrase independent bicarbonate reabsorption. In free flow experiments during systemic application of carbonic anhydrase inhibitor benzolamide (50 mg/kg B. W.) bicarbonate recovery in % of filtered load was found to be 74±8% in late proximal convoluted tubules, 39±6% in distal convoluted tubules and 32±4% in urine, indicating that most of carbonic anhydrase independent bicarbonate reabsorption occurs in tubule segments prior to distal convoluted tubules. In vivo continuous microperfusion experiments in proximal convoluted tubules demonstrated that luminal benzolamide (0.5 mmol/l) virtually abolishes net bicarbonate fluxes, when bicarbonate concentration in the luminal perfusate (25 mmol/l) is close to peritubular plasma concentration (24.4 mmol/l). In contrast, a significant downhill reabsorptive flux occurs, when perfusate bicarbonate concentration is 75 mmol/l and a significant downhill secretory flux is observed, when the perfusate is initially free of bicarbonate. The corresponding apparent permeabilities are 1.0±0.1·10−6 cm2/s for influx and 1.6±0.4·10−6 cm2/s for efflux of bicarbonate. Clearance studies reveal that carbonic anhydrase dependent and independent bicarbonate reabsorption are not saturable but depend on the rate of volume reabsorption in the kidney. In conclusion, passive movements of bicarbonate do occur in proximal convoluted tubules and most likely contribute to carbonic anhydrase independent bicarbonate reabsorption.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00584724
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  • 7
    Electronic Resource
    Electronic Resource
    Evidence for a bicarbonate leak in the proximal tubule of the rat kidney (1980)
    Springer
    Pflügers Archiv 386 (1980), S. 239-244 
    Details
    ISSN: 1432-2013
    Keywords: Bicarbonate transport ; Proximal tubule ; Rat kidney ; Antimony microelectrode ; Micro-Astrup ; Benzolamide ; Micropuncture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To elucidate the mechanism responsible for the establishment of steady state pH at zero net flux (pH∞) in proximal convoluted tubules, luminal pH was recorded continuously with antimony microelectrodes under three experimental conditions. First: luminal pH in stationary droplets was allowed to reach pH∞ (6.76±0.07) and then carbonic anhydrase inhibitor benzolamide (3·10−3 mol/l) was superfused on the kidney surface. Following application of benzolamide, luminal pH decreased within seconds (ΔpH=−0.27±0.03 SEM). Second: tubule segments were perfused continuously with MES-buffer containing solution set to a pH of 6.1. Some 1–2 mm distal to the perfusion pipette luminal pH was recorded and was 6.5±0.04. After superfusion of benzolamide (3·10−3 mol/l) pH decreased (ΔpH=−0.15±0.03). Third: pH in stationary droplets was again allowed to reach pH∞ (6.69±0.01) and bicarbonate and CO2-free solution (5 mmol/l phosphate set to a pH of 7.4) was microinfused into the adjacent peritubular capillary. Luminal pH again decreased almost immediately (ΔpH=−0.23±0.02). The data are interpreted as evidence for a bicarbonate leak. In a fourth series of experiments, segments of proximal tubules were perfused under benzolamide (0.4·10−6 mol/min) with solutions initially free of bicarbonate or other buffers. In the collected fluid, bicarbonate was determined by a micro-Astrup method. A significant increase of luminal bicarbonate concentration (r=0.88) indicates a permeability of 0.98±0.14·10−6 cm2/s of the tubular wall for bicarbonate. Since bicarbonate eventually increases more than 3-fold the equilibrium concentration, collected bicarbonate could not have been formed by H2CO3 or CO2. Bicarbonate enters the luminal fluid and reacts with secreted hydrogen ions to form carbonic acid. It, therefore, buffers secreted hydrogen ions and increases luminal pH at or below steady state. Inhibition of carbonic anhydrase and lowering of peritubular bicarbonate thus lower pH∞.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00587474
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