Similar chloride channels in the connecting tubule and cortical collecting duct of the mouse kidney
Using the patch-clamp technique, we investigated Cl− channels on the basolateral membrane of the connecting tubule (CNT) and cortical collecting duct (CCD). We found a ∼10-pS channel in CNT cell-attached patches. Substitution of sodium gluconate for NaCl in the pipette shifted the reversal potential by +25 mV, whereas N-methyl-d-gluconate chloride had no effect, indicating anion selectivity. On inside-out patches, we determined a selectivity sequence of Cl− > Br− ∼ NO3− > F−, which is compatible with that of ClC-K2, a Cl− channel in the distal nephron. In addition, the number of open channels ( NPo) measured in cell-attached patches was significantly increased when Ca2+ concentration or pH in the pipette was increased, which is another characteristic of ClC-K. These findings suggest that the basis for this channel is ClC-K2. A similar Cl− channel was found in CCD patches. Because CNT and CCD are heterogeneous tissues, we studied the cellular distribution of the Cl− channel using recording conditions (KCl-rich solution in the pipette) that allowed us to detect simultaneously Cl− channels and inwardly rectifying K+ channels. We detected Cl− channels alone in 45% and 42% and K+ channels alone in 51% and 58% of CNT and CCD patches, respectively. Cl− and K+ channels were recorded simultaneously from two patches (4% of patches) in the CNT and from none of the patches in the CCD. This indicates that Cl− and K+ channels are located in different cell types, which we suggest may be the intercalated cells and principal cells, respectively.