The chloride-conductive properties of the isolated rabbit cortical collecting duct were assessed with microelectrode techniques. The transepithelial, apical, and basolateral membrane potential differences, V(te), Va, and Vb, respectively, were monitored continuously along with periodic measurements of the transepithelial conductance, G(te), and fractional resistance, fRa (ratio of apical to apical plus basolateral membrane resistance). Active transport was eliminated in all experiments by luminal addition of 50 μM amiloride in HCO3-free solutions. Upon reducing the chloride activity in the bath (gluconate replacement), there was a marked depolarization of Vb and decrease in G(te) and fRa, demonstrating a major dependence of the basolateral membrane conductance on the bath chloride activity. However, a significant K+ conductance at that barrier was also apparent since raising the bath K+ concentration caused an increase in G(te) and fRa and depolarization of Vb. Lowering the chloride activity of the perfusate caused a consistent decrease of G(te) but not of fRa, effects consistent with a high Cl- conductance of the tight junction and little, if any, apical membrane Cl- conductance. By use of the Cl-dependent conductances, the Cl- permeabilities at equilibrium were estimated to be near 1.0 x 10-5 cm.s-1 for the tight junction, P(Cl)(tj), and 5 x 10-5 cm.s-1 for the basolateral cell membrane, P(Cl)b. It is concluded that the paracellular pathway provides a major route for transepithelial Cl- transport. Furthermore, since the isotopically measured Cl- permeability is severalfold greater than P(Cl)(tj), a significant transcellular flux of Cl- must exist, implicating a neutral exchange mechanism at the apical cell membrane in series with the high basolateral membrane Cl- conductance.
|Original language||English (US)|
|Journal||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|State||Published - 1984|
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