Biology subjects

Dinh, H. A.

Publications and source records attributed to Dinh, H. A..

3 recordsLinked to original sources

bioRxiv2025

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, 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.

physiology↗

bioRxiv2024

Expression and Function of Connexin 43 and Connexin 37 in the Murine Zona Glomerulosa

The zona glomerulosa (ZG) synthesizes the mineralocorticoid aldosterone. The primary role of aldosterone is the maintenance of volume and electrolyte homeostasis. Aldosterone synthesis is primarily regulated via tightly controlled oscillations in intracellular calcium levels in response to stimulation. It has previously been shown that calcium oscillations are synchronized through mechanical linkage between adjacent ZG cells. In many other cell types, similar synchronization is rather dependent on gap junctions (GJ). The recent discovery of mutations in CADM1 was linked to impaired GJ function in the ZG. Based on published transcriptomics data, we re-examined the presence and functional impact of GJ in the ZG. We found evidence for the expression of connexin 43 and 37 in the ZG in microarray data, in-situ hybridization and immunohistology. Calcium oscillations in ZG rosettes showed some degree of synchronization as reported previously. Unspecific GJ inhibition only had a small impact on this synchronicity. However, no signs of connections between cytosols could be observed as indicated by the lack of fluorescence recovery after photobleaching. We conclude that, while connexin proteins are expressed in the ZG, functional GJ in the physiological ZG are rare and of little consequence for calcium signaling.

physiology↗

bioRxiv2023

T- and L-type calcium channels maintain calcium oscillations in the murine zona glomerulosa

The zona glomerulosa of the adrenal gland is responsible for the synthesis and release of the mineralocorticoid aldosterone. This steroid hormone regulates salt reabsorption in the kidney and blood pressure. The most important stimuli of aldosterone synthesis are the serum concentrations of angiotensin II and potassium. In response to these stimuli, voltage and intracellular calcium levels in the zona glomerulosa oscillate, providing the signal for aldosterone synthesis. It was proposed that the voltage-gated T-type calcium channel CaV3.2 is necessary for the generation of these oscillations. However, Cacna1h knockout mice have normal plasma aldosterone levels, suggesting additional calcium entry pathways. We used a combination of calcium imaging, patch clamp and RNA sequencing to investigate such pathways in the murine zona glomerulosa. Cacna1h-/- glomerulosa cells still showed calcium oscillations with similar concentrations as wild-type mice. No calcium channels or transporters were upregulated to compensate for the loss of CaV3.2. The calcium oscillations observed were instead dependent on L-type voltage-gated calcium channels. Furthermore, we found that L-type can also partially compensate for an acute inhibition of CaV3.2 in wild-type mice. Only inhibition of both, T- and L-type calcium channels abolished the increase of intracellular calcium caused by angiotensin II in wild-type. Our study demonstrates that T-type calcium channels are not strictly required to maintain glomerulosa calcium oscillations and aldosterone production and pharmacological inhibition of T-type channels alone will likely not significantly impact aldosterone production over time.

physiology↗