Anion permeabilities of the isolated perfused XXXX proximal tubule.

@entity20412 @entity28056 @entity1372 @entity3157 @entity95 @entity2865
Electrophysiologic and isotopic techniques were used to characterize the anion permeabilities of isolated perfused @entity95 proximal tubules (S2 segments). Tubules were differentiated into @entity2865 - and @entity1372 -selective populations by electrophysiologic rather than by anatomic criteria. The tubules were studied under conditions that inhibited active @entity1372 transport. The isotopic @entity2865 permeability coefficient was 5.5 +/- 0.6 X 10(-5) cm/s (n = 19) for @entity2865 -selective tubules and 3.2 +/- 0.6 X 10(-5) cm/s (n = 15) for @entity1372 -selective tubules. The @entity20412 permeability coefficient was 1.1 +/- 0.2 X 10(-5) cm/s (n = 23) and did not vary with @entity1372 or @entity2865 selectivity. The variation of oxyanion permeability ( @entity3157 , @entity20412 , and @entity28056 ) relative to @entity2865 resulted from changes in @entity2865 permeability, per se, rather than any change in the oxyanion permeability. A consistent relation between @entity3157 and @entity20412 permeability permitted the permeability of @entity3157 ion to be estimated at 1.3 X 10(-5) cm/s. The mechanism of ion selectivity appears to be different for the two populations of tubules. @entity2865 -selective tubules appear to hve relatively small pathways that do not contain fixed-charge sites. In contrast, @entity1372 -selective tubules may have permeation pathways that contain fixed negative-charge sites.
