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• Phosphate transport  (4)
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• 1
Electronic Resource
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
Electronic Resource
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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• 3
Electronic Resource
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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• 4
Electronic Resource
Springer
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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