Intrinsic Adrenal TWIK-Related Acid-Sensitive TASK Channel Dysfunction Produces Spontaneous Calcium Oscillations Sufficient to Drive AngII (Angiotensin II)-Unresponsive Hyperaldosteronism

Abstract

BACKGROUND: Ion channel mutations in calcium regulating genes strongly associate with AngII (angiotensin II)-independent aldosterone production. Here, we used an established mouse model of in vivo aldosterone autonomy, Cyp11b2 -driven deletion of TWIK-related acid-sensitive potassium channels (TASK-1 and TASK-3, termed zona glomerulosa [zG]-TASK-loss-of-function), and selective pharmacological TASK channel inhibition to determine whether channel dysfunction in native, electrically excitable zG cell rosette-assemblies: (1) produces spontaneous calcium oscillatory activity and (2) is sufficient to drive substantial aldosterone autonomy. METHODS: We imaged calcium activity in adrenal slices expressing a zG-specific calcium reporter (GCaMP3), an in vitro experimental approach that preserves the native rosette assembly and removes potentially confounding extra-adrenal contributions. In parallel experiments, we measured acute aldosterone production from adrenal slice cultures. RESULTS: Absent from untreated WT slices, we find that either adrenal-specific genetic deletion or acute pharmacological TASK channel inhibition produces spontaneous oscillatory bursting behavior and steroidogenic activity (2.4-fold) that are robust, sustained, and equivalent to activities evoked by 3 nM AngII in WT slices. Moreover, spontaneous activity in zG-TASK-loss-of-function slices and inhibitor-evoked activity in WT slices are unresponsive to AngII regulation over a wide range of concentrations (50 pM to 3 µM). CONCLUSIONS: We provide proof of principle that spontaneous activity of zG cells within classic rosette assemblies evoked solely by a change in an intrinsic, dominant resting-state conductance can be a significant source of AngII-independent aldosterone production from native tissue.

Physiological and pathophysiological roles of the KCNK3 potassium channel in the pulmonary circulation and the heart

“…The adult Kcnk3 −/− female mice develop severe hyperaldosteronism caused by an adrenocortical zonation defect (Heitzmann et al., 2008). Compared to wild‐type mice, aldosterone production is elevated in zona glomerulosa slices from kcnk3 −/− mice and is not regulated by angiotensin II (Gancayco et al., 2022). In contrast, aldosterone production seems unchanged in Kcnk3 deficient rats (males or females) compared to wild‐type (Lambert et al., 2019), highlighting the difference between species in the regulation of aldosterone production by KCNK3.…”

T- and L-Type Calcium Channels Maintain Calcium Oscillations in the Murine Zona Glomerulosa

“…It had already been suggested that additional conductances must underlie the initial depolarization in WT, 3 and this is confirmed by our results, as L-type channels (Ca V 1.3 and even more so 1.2) require stronger depolarization for activation than T-type VGCCs and are unlikely to drive depolarization from a potassium-defined resting membrane potential on their own. Clearly, the closure of TASK potassium channels is involved in permitting (Ang II-dependent) depolarization, 5,6,44 but still other, currently unknown, conductances must mediate the initial depolarization itself. Also, it is currently unclear how individual spikes and bursts are terminated.…”