Paracellular pathway of rabbit cortical collecting tubule (CCT): a high resistance, non-selective barrier
Previous studies have suggested that the paracellular pathway of CCT is Cl selective. We reassessed this issue under conditions in which the cellular Na and K conductive pathways were blocked by lumen amiloride (50 ..mu..M) and Ba/sup + +/ (4 mM). The residual transepithelial conductance (G/sub T/, 1.10 +- 0.09 mS cm/sup -2/) is a reasonable estimate of the paracellular conductance. Three independent assessments of the barrier selectivity were used. First, the effect of symmetrical replacement of Na (TMA, bis (2-hydroxy ethyl) dimethylammonium) or Cl (NO/sub 3/, gluconate) on G/sub T/ was determined. All test solutions decreased G/sub T/, and in each case the decrease could be accounted for by the lower conductivity of the test solution relative to NaCl. Thus, the pathway does not select one cation or one anion over another. Second, lumen-to-bath /sup 22/Na and /sup 36/Cl fluxes were measured with 0 Cl/0 HCO/sub 3/ bath to eliminate cellular Cl flux. The ratio J/sub Na/J/sub Cl/ (0.75 +- 0.14) was not different from the ratio of Na/Cl mobilities in water (0.65), and the sum of the calculated partial ionic conductances of Na and Cl adequately approximated the measured G/sub T/. Third, NaCl concentration was sequentially lowered in lumen or bath. In the presence of bath ouabain, P/sub Na//P/sub Cl/, calculated from dilution voltages was 0.67 +- .02. The paracellular pathway of CCT is non-selective for anions over cations.
- Research Organization:
- Univ. of Iowa, Iowa City
- OSTI ID:
- 5450908
- Report Number(s):
- CONF-8604222-; TRN: 86-028366
- Journal Information:
- Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States), Vol. 45:3; Conference: 70. annual meeting of the Federation of American Society for Experimental Biology, St. Louis, MO, USA, 13 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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550201* - Biochemistry- Tracer Techniques