ClC-2 Contributes to Hypotonicity-Induced Adrenal Aldosterone Secretion

The zona glomerulosa (ZG) of the adrenal cortex regulates blood pressure and electrolyte homeostasis through aldosterone production. In ZG cells, 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.

We used Clcn2 knockout (KO) and wild-type (WT) mice. Explanted adrenal glands were incubated with iso- and hypotonic solutions for measurements of aldosterone. Acute adrenal slices were studied using calcium and chloride sensitive fluorescent dyes. We also investigated ClC-2's systemic importance by inducing a hyponatremic hypoosmolality in mice using desmopressin.

Under hypoosmolar conditions, WT adrenals upregulated aldosterone production in vitro, an effect that was absent in the KO. WT cells responded to hypoosmolality with increased intracellular calcium levels. This response was abrogated in KO cells. Intracellular chloride levels were higher in ZG cells from KO adrenal slices. This suggests that ClC-2 provides a hypoosmolality-dependent chloride efflux pathway that is missing in the KO. Systemic hypoosmolality in mice induced by desmopressin did not differentially affect blood aldosterone levels.

ClC-2 plays a role in the ZG's response to reduced extracellular osmolality through chloride outflow, which likely causes depolarization, voltage-dependent calcium influx, and aldosterone production. These data advance our understanding of regulators of aldosterone production.