scholarly journals Organic substrate effects on and heterogeneity of Necturus proximal tubule function

1980 ◽  
Vol 17 (4) ◽  
pp. 479-490 ◽  
Author(s):  
Jameson Forster ◽  
Paul S. Steels ◽  
Emile L. Boulpaep
Keyword(s):  
Proximal Tubule ◽  
Organic Substrate ◽  
Substrate Effects ◽  
Necturus Proximal Tubule

Dissociation of proximal tubular glucose and Na+ reabsorption by amphotericin B

1979 ◽  
Vol 236 (4) ◽  
pp. F392-F397
Author(s):  
P. S. Aronson ◽  
J. P. Hayslett ◽  
M. Kashgarian
Keyword(s):  
Proximal Tubule ◽  
Glucose Uptake ◽  
Amphotericin B ◽  
Membrane Vesicle ◽  
Membrane Vesicles ◽  
Na Transport ◽  
Glucose Reabsorption ◽  
Tubular Lumen ◽  
Proximal Tubular ◽  
Necturus Proximal Tubule

The effect of amphotericin B on glucose and Na+ transport was studied in the Necturus proximal tubule and in microvillus membrane vesicles isolated from the rabbit renal cortex. In the Necturus experiments, the rate constants for disappearance of radiolabeled glucose (kG) and mannitol (kM) from the tubular lumen were determined by stop-flow microperfusion. Saturability and Na+-dependence of glucose reabsorption was confirmed, since kG was reduced by raising intratubular glucose from 1 to 5 mM or by replacing intratubular Na+ with choline. Neither maneuver affected kM. Intratubular amphotericin B (10 microgram/ml), previously shown to stimulate active Na+ reabsorption in the Necturus proximal tubule, inhibited kG with no effect on kM. In the membrane vesicle preparation, amphotericin inhibited the uphill glucose uptake which results from imposing a NaCl gradient from outside to inside, but had no effect on glucose uptake in either the absence of Na+ or in the presence of Na+ when there was no Na+ gradient. Amphotericin B stimulated the uptake of Na+ by the vesicles. The observed dissociation of glucose and Na+ transport by amphotericin B is consistent with the concept that proximal tubular glucose reabsorption is energized by the luminal membrane Na+ gradient and is not directly linked to active Na+ transport per se.

Nonelectrolyte permeability of the paracellular pathway in Necturus proximal tubule

1975 ◽  
Vol 228 (2) ◽  
pp. 581-595 ◽  
Author(s):  
CA Berry ◽  
EL Boulpaep
Keyword(s):  
Tight Junction ◽  
Proximal Tubule ◽  
Water Flow ◽  
Volume Flow ◽  
Osmotic Gradient ◽  
Osmotic Water ◽  
Net Flux ◽  
Gradient Measurements ◽  
Paracellular Shunt ◽  
Necturus Proximal Tubule

Micropuncture experiments were performed on Necturus proximal tubule using stationary microperfusion and microrecollection techniques. The transepithelial movement of the extracellular marker, sucrose, was used to investigate the passive permeability of the paracellular shunt pathway under steady-state conditions, during spontaneous reabsorption and water flow induced by an external osmotic gradient. Measurements were made of the sucrose permeability (P-s) efflux, net flux, and of net volume flow. True P-s determined in the absence of net volume flow and transepithelial gradient was 0.96 10-6 cm s-1. Both ouabain and isotonic volume expansion decreased shunt P-s. During reabsorption, solute-coupled water flow increased apparent P-s and net sucrose flux equalled efflux. Osmotic water flow from lumen to plasma decreased apparent P-s, with net sucrose flux equal to efflux; whereas osmotic flow from plasma to lumen increased apparent P-s but no net flux was observed. It is concluded that changes in P-s can be interpreted as relative alterations of the tight junction and the lateral spaces and that a portion of the volume flow from lumen to plasma proceeds via the tight junction.

Fluid reabsorption by Necturus proximal tubule perfused with solutions of normal and reduced osmolarity

1982 ◽  
Vol 215 (1201) ◽  
pp. 411-431 ◽  
Keyword(s):  
Proximal Tubule ◽  
Experimental Results ◽  
Fluid Absorption ◽  
Perfusion Fluid ◽  
Fluid Reabsorption ◽  
Osmotic Permeability ◽  
Osmotic Equilibration ◽  
Tubule Wall ◽  
Na Uptake ◽  
Necturus Proximal Tubule

Fluid absorption in Necturus proximal tubule was studied when the kidneys were perfused with solutions of different osmolarities. The rate of fluid absorption was inversely proportional to the perfusion fluid osmolarity, while Na uptake remained constant. No difference was detected between the collected and injected luminal fluid, i. e. reabsorption was isotonic at normal and reduced osmolarities. The transtubular osmotic permeability remained fairly constant under the different per­fusion osmolarities. Using our experimental results to test various models based on osmotic equilibration across the tubule wall we show that none of these provides an adequate mechanism for fluid absorption in this epithelium.

Permeability changes in Necturus proximal tubule during volume expansion

1978 ◽  
Vol 234 (3) ◽  
pp. F225-F234 ◽  
Author(s):  
C. J. Bentzel ◽  
P. R. Reczek
Keyword(s):  
Proximal Tubule ◽  
Volume Expansion ◽  
Dominant Role ◽  
Extracellular Volume ◽  
Water Flux ◽  
Apical Surface ◽  
Osmotic Flow ◽  
Flow Parameters ◽  
Diffusional Permeability ◽  
Necturus Proximal Tubule

The permeability of Necturus proximal tubule to hydrophilic nonelectrolytes of varying molecular size was studied under control conditions and during isotonic expansion of the animal's extracellular volume. Transepithelial permeability was measured in perfused tubular segments under conditions of zero net water flux. During volume expansion, tubular permeability to urea increased slightly, whereas mannitol decreased slightly and permeability to sucrose was significantly decreased. Volume expansion had a greater effect on osmotic flow parameters; the NaCl reflection coefficient decreased from 0.64 to 0.47 (summer animals) and from 0.41 to 0.27 (winter animals). Osmotic water flux and hydraulic conductivity increased but only in the lumen-to-capillary direction. Reflection coefficients of nonelectrolytes measured at the apical surface were reduced during volume expansion for probing molecules greater than 3 A in radius and were unchanged for smaller molecules, less than 3 A, suggesting two pore populations. We propose that an increase in tight-junction permeability can account for modification of osmotic flow parameters, whereas the whole thickness of the epithelium, particularly the intercellular space, plays the dominant role in regulation of diffusional permeability.

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