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  • impedance analysis  (1)
  • intestinal absorption  (1)
  • 1
    Electronic Resource
    Electronic Resource
    Physiological regulation of transepithelial impedance in the intestinal mucosa of rats and hamsters (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 137-148 
    Details
    ISSN: 1432-1424
    Keywords: intestinal epithelium ; epithelial impedance ; paracellular pathways ; glucose-controlled permeability ; brushborder contraction ; impedance analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Isolated intestinal segments from rats or hamsters were recirculated with balanced salt solutions containing fluorocarbon emulsion to provide 6 vpc oxygen. The lumen contained an axial Ag−AgCl electrode, and the serosal surface was surrounded by a cylindrical shell of Ag−AgCl. Transmural impedances were measured at frequencies from 0.01–30 kHz before and after removal of the mucosal epithelium. The resistance of intercellular junctions,R J , the distributed resistance of the lateral spaces,R L , and the distributed membrane capacitance,C M , were computed from the relations between frequency and impedance. Activation of Na-coupled solute transport by addition of glucose, 3-0-methyl glucose, alanine or leucine caused two- to threefold decreases of transepithelial impedance. Typical changes induced by glucose in hamster small intestine wereR J 30→13 Ω,R L 23→10 Ω, andC M 8→20 μF (per cm length of segment). Half maximal response occurred at a glucose concentration of 2–3mm. The area per unit path length of the junctions (Ap/Δx=specific resistance ÷R J ) in glucose activated epithelium was 3.7 cm in hamster midgut and 6.8 cm in rat. These values are close to the 4.3 cm estimated independently from coefficients of solvent drag and hydrodynamic conductance in glucose-activated rat intestine in vivo. The transepithelial impedance response to Na-coupled solute transport was reversibly dependent upon oxygen tension. It is proposed that activation of Na-coupled solute transport triggers contraction of circumferential actomyosin fibers in the terminal web of the microvillar cytoskeletal system, thereby pulling apart junctions and allowing paracellular absorption of nutrients by solvent drag as described in the previous accompanying paper. Anatomical evidence in support of this hypothesis is presented in the following second accompanying paper.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209146
    Library Location Call Number Volume/Issue/Year Availability
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Contribution of solvent drag through intercellular junctions to absorption of nutrients by the small intestine of the rat (1987)
    Springer
    The journal of membrane biology 100 (1987), S. 123-136 
    Details
    ISSN: 1432-1424
    Keywords: intestinal absorption ; paracellular pathways ; solvent drag ; epithelial permeability ; intercellular junctions ; molecular sieving
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The lumen of the small intestine in anesthetized rats was recirculated with 50 ml perfusion fluid containing normal salts, 25mm glucose and low concentrations of hydrophilic solutes ranging in size from creatinine (mol wt 113) to Inulin (mol wt 5500). Ferrocyanide, a nontoxic, quadrupally charged anion was not absorbed; it could therefore be used as an osmotically active solute with reflection coefficient of 1.0 to adjust rates of fluid absorption,J v , and to measure the coefficient of osmotic flow,L p . The clearances from the perfusion fluid of all other test solutes were approximately proportional toJ v . FromL p and rates of clearances as a function ofJ v and molecular size we estimate (a) the fraction of fluid absorption which passes paracellularly (approx. 50%), (b) coefficients of solvent drag of various solutes within intercellular junctions, (c) the equivalent pore radius of intercellular junctions (50 Å) and their cross sectional area per unit path length (4.3 cm per cm length of intestine). Glucose absorption also varied as a function ofJ v . From this relationship and the clearances of inert markers we calculate the rate of active transport of glucose, the amount of glucose carried paracellularly by solvent drag or back-diffusion at any givenJ v and luminal glucose concentration and the concentration of glucose in the absorbate. The results indicate that solvent drag through paracellular channels is the principal route for intestinal transport of glucose or amino acids at physiological rates of fluid absorption and concentration. In the absence of luminal glucose the rate of fluid absorption and the clearances of all inert hydrophilic solutes were greatly reduced. It is proposed that Na-coupled transport of organic solutes from lumen to intercellular spaces provides the principal osmotic force for fluid absorption and triggers widening of intercellular junctions, thus promoting bulk absorption of nutrients by solvent drag. Further evidence for regulation of channel width is provided in accompanying papers on changes in electrical impedance and ultrastructure of junctions during Na-coupled solute transport.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02209145
    Library Location Call Number Volume/Issue/Year Availability
    BibTip Others were also interested in ...
    Paper (German National Licenses)
    Fulltext
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