ClC-2 contributes to hypotonicity-induced adrenal aldosterone secretion

Abstract

The zona glomerulosa (ZG) of the adrenal cortex regulates blood pressure and electrolyte homeostasis through aldosterone production. In ZG cells, the serum concentrations of potassium and angiotensin II (Ang II) trigger calcium oscillations that drive aldosterone synthesis. Changes in serum osmolality also modulate aldosterone production in a chloride-dependent fashion, but the involved proteins remain unclear. Because the chloride channel ClC-2 is activated by hypoosmolality, we investigated its role in ZG osmoregulation using ClC-2 knockout (KO) mice. Intracellular chloride concentrations in the ZG are high, and opening of ClC-2 leads to chloride efflux, depolarization and voltage-dependent calcium influx. Under hypoosmolar conditions, intracellular chloride levels were higher in ClC-2 KO ZG cells than in the WT, suggesting that hypoosmolality triggers chloride efflux via ClC-2 in the WT, and that this efflux is absent in the KO. WT cells responded to hypoosmolality with an increase in intracellular calcium levels, likely mediated by chloride efflux and depolarization. This response was again abrogated in the KO, despite faster calcium spiking. In line with increased intracellular calcium levels, WT adrenal slices upregulated aldosterone production upon hypoosmolar treatment in vitro, whereas aldosterone production remained unchanged in the KO. These findings establish a role for ClC-2 in the ZGs response to reductions in extracellular osmolality through the outflow of chloride, voltage-dependent calcium influx and aldosterone production, advancing our general understanding of regulators of aldosterone production and the specific role of ClC-2.