Key result
In a transgenic mouse model, basal intracellular Cl- concentration in the distal convoluted tubule was ~7 mM, and was modulated by altering ClC-K2, KCC, and Kir4.1/5.1 activity.
Why the study?
Although intracellular Cl- regulates WNK and NCC, intracellular Cl- concentrations had not been directly measured in the mammalian distal convoluted tubule.
In a transgenic mouse model, intracellular chloride concentration in the distal convoluted tubule is modulated by K+ channels and transporters including ClC-K2, KCC, and Kir4.1/5.1.
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−]i) have not been directly measured in the mammalian DCT. Therefore, to measure [Cl−]iin 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−]iwas ~7 mM. Stimulation of Cl−exit with low-Cl−hypotonic solutions decreased [Cl−]i, whereas inhibition of KCC by DIOA or inhibition of ClC-K2 by NPPB increased [Cl−]i, suggesting roles for both KCC and ClC-K2 in the modulation of [Cl−]i. Blockade of basolateral K+channels (Kir4.1/5.1) with barium significantly increased [Cl−]i. Finally, a decrease in extracellular K+concentration transiently decreased [Cl−]i, whereas raising extracellular K+transiently increased [Cl−]i, further suggesting a role for Kir4.1/5.1 in the regulation of [Cl−]i. We conclude that the alteration in ClC-K2, KCC, and Kir4.1/5.1 activity influences [Cl−]iin the DCT.
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Su et al. (2020) studied this question. Alteration of K+ channels and transporters (e.g., DIOA, NPPB, barium, altered extracellular K+) vs. Basal measurements was evaluated on Intracellular Cl- concentration ([Cl-]i) in DCT cells. In a transgenic mouse model, basal intracellular Cl- concentration in the distal convoluted tubule was ~7 mM, and was modulated by altering ClC-K2, KCC, and Kir4.1/5.1 activity.
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