Distal convoluted tubule Cl - concentration is modulated via K + channels and transporters

Cl -sensitive with-no-lysine kinase (WNK) plays a key role in regulating the thiazide-sensitive Na -Cl cotransporter (NCC) in the distal convoluted tubule (DCT). Cl enters DCT cells through NCC and leaves the cell across the basolateral membrane via the Cl channel ClC-K2 or K -Cl cotransporter (KCC). While KCC is electroneutral, Cl exit via ClC-K2 is electrogenic. Therefore, an alteration in DCT basolateral K channel activity is expected to influence Cl movement across the basolateral membrane. Although a role for intracellular Cl in the regulation of WNK and NCC has been established, intracellular Cl concentrations ([Cl ] ) have not been directly measured in the mammalian DCT. Therefore, to measure [Cl ] in DCT cells, we generated a transgenic mouse model expressing an optogenetic kidney-specific Cl-Sensor and measured Cl fluorescent imaging in the isolated DCT. Basal measurements indicated that the mean [Cl ] was ~7 mM. Stimulation of Cl exit with low-Cl hypotonic solutions decreased [Cl ] , whereas inhibition of KCC by DIOA or inhibition of ClC-K2 by NPPB increased [Cl ] , suggesting roles for both KCC and ClC-K2 in the modulation of [Cl ] . Blockade of basolateral K channels (Kir4.1/5.1) with barium significantly increased [Cl ] . Finally, a decrease in extracellular K concentration transiently decreased [Cl ] , whereas raising extracellular K transiently increased [Cl ] , further suggesting a role for Kir4.1/5.1 in the regulation of [Cl ] . We conclude that the alteration in ClC-K2, KCC, and Kir4.1/5.1 activity influences [Cl ] in the DCT.