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* To whom correspondence should be addressed. E-mail: martine.imbert-teboul{at}bhdc.jussieu.fr.
The distal convoluted tubule is a heterogeneous segment subdivided into early (DCT1) and late (DCT2) parts, depending on the distribution of various transport systems. We do not have an exhaustive picture of the Cl- channels on the basolateral side: the presence of ClC-K2 channels is generally accepted, whereas that of ClC-K1 remains controversial. We used here single-cell RT-PCR and patch-clamp to probe Cl--channels heterogeneity in microdissected mouse DCT at the molecular and functional levels. Our findings show that 63% of the DCT cells express ClC-K2 mRNA, either alone (type-1 cells: 47 and 23% in DCT1 and DCT2, respectively), or combined with ClC-K1, mostly in DCT2 (type-2 cells: 33%), but 37% of DCT1 and DCT2 cells do not express any ClC-K. Patch-clamp experiments revealed that a Cl- channel, with 9-pS conductance and Cl-> NO3- = Br- anion selectivity sequence, is present in the DCT1 and DCT2 basolateral membranes (87 and 71% of the patches, respectively). This dominant channel is likely to be ClC-K2 in type-1 cells. In type-2 cells, it could be ClC-K2 and/or ClC-K1 homo-dimers, but also ClC-K1/ClC-K2 hetero-dimers, or a mixture of all combinations. A second, distinct Cl- channel (13% of DCT1 patches, 29% of DCT2 patches) also displayed 9-pS conductance, but had a completely different anion selectivity (I- > NO3- > Br- > Cl-), which was not compatible with that of the ClC-Ks. This indicates that a Cl- channel that is unlikely to belong to the ClC family may also be involved in Cl- absorption in the DCT2.
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