Ion selectivity and proximal salt reabsorption

Academic Article

Abstract

  • Electrophysiological techniques were used in isolated perfused superficial (S) and juxtamedullary (JM) rabbit proximal convoluted tubules (PCT) to examine the relative sodium-to-chloride (P(Na)/P(Cl)) and bicarbonate-to-chloride (P(HCO3)/P(Cl) permeability ratios. We found that the great majority of PCT are sodium selective and that P(HCO3)/P(Cl) depends on the experimental conditions. In the presence of active sodium transport, P(HCO3)/P(Cl) is high and increases with P(Na)/P(Cl). When P(HCO3)/P(Cl) is determined after inhibition of active sodium transport or at 25°C, P(HCO3)/P(Cl) approximates the free solution anion mobility ratio of 0.5 and is independent of P(Na)/P(Cl). The difference between P(HCO3)/P(Cl) determined in the presence of and in the absence of active transport suggests that the lowering of bath bicarbonate concentration in the presence of active transport changes both paracellular and transcellular current flow. In addition, we found that during luminal perfusion with high chloride, low bicarbonate, organic solute-free solutions, the transepithelial electrical potential depends on P(Na)/P(Cl) and P(HCO3)/P(Cl). This potential is approximately 4.0 mV in S PCT with low P(Na)/P(Cl) and falls progressively to zero in JM PCT with high P(Na)/P(Cl). From these data we conclude than anion concentration gradients drive an important diffusive flux of sodium chloride through the paracellular pathway only in PCT with low P(Na)/P(Cl) ratios.
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    Digital Object Identifier (doi)

    Author List

  • Berry CA; Warnock DG; Rector FC
  • Volume

  • 4
  • Issue

  • 3