When inappropriate for salt status, the mineralocorticoid aldosterone induces cardiac and renal injury. Autonomous overproduction of aldosterone from the adrenal zona glomerulosa (ZG) is also the most frequent cause of secondary hypertension. Yet, the etiology of nontumorigenic primary hyperaldosteronism caused by bilateral idiopathic hyperaldosteronism remains unknown. Here, we show that genetic deletion of TWIK-related acid-sensitive K (TASK)-1 and TASK-3 channels removes an important background K current that results in a marked depolarization of ZG cell membrane potential. Although TASK channel deletion mice (TASK ^−/− ) adjust urinary Na excretion and aldosterone production to match Na intake, they produce more aldosterone than control mice across the range of Na intake. Overproduction of aldosterone is not the result of enhanced activity of the renin–angiotensin system because circulating renin concentrations remain either unchanged or lower than those of control mice at each level of Na intake. In addition, TASK ^−/− mice fail to suppress aldosterone production in response to dietary Na loading. Autonomous aldosterone production is also demonstrated by the failure of an angiotensin type 1 receptor blocker, candesartan, to normalize aldosterone production to control levels in TASK ^−/− mice. Thus, TASK ^−/− channel knockout mice exhibit the hallmarks of primary hyperaldosteronism. Our studies establish an animal model of nontumorigenic primary hyperaldosteronism and identify TASK channels as a possible therapeutic target for primary hyperaldosteronism.

Aldosterone, which plays a central role in the regulation of blood pressure, is produced by zona glomerulosa (ZG) cells of the adrenal gland. When dysregulated, aldosterone is pathogenic and contributes to the development and progression of cardiovascular and renal disease. Although sustained production of aldosterone requires persistent Ca²⁺ entry through low-voltage activated Ca²⁺ channels, isolated ZG cells are considered nonexcitable, with recorded membrane voltages that are too hyperpolarized to permit Ca²⁺ entry. Here, we show that mouse ZG cells within adrenal slices spontaneously generate membrane potential oscillations of low periodicity. This innate electrical excitability of ZG cells provides a platform for the production of a recurrent Ca²⁺ signal that can be controlled by Ang II and extracellular potassium, the 2 major regulators of aldosterone production. We conclude that native ZG cells are electrical oscillators, and that this behavior provides what we believe to be a new molecular explanation for the control of Ca²⁺ entry in these steroidogenic cells.

The entry of extracellular Ca²⁺, which is mediated by Ca²⁺ release-activated Ca²⁺ (CRAC) channels, is essential for T cell activation and the normal functioning of other immune cells. Although the molecular components of CRAC channels, the Orai1 pore-forming subunit and the STIM1-activating subunit have been recently identified, the gating mechanism by which Orai1 channels conduct Ca²⁺ entry upon Orai1-STIM1 interaction following Ca²⁺ store release remains elusive. Herein, we show that C-terminal truncations or point mutations prevented Orai1 from binding to STIM1 and subsequent channel opening. In contrast, an Orai1 mutant with an N-terminal truncation interacted with but failed to be activated by STIM1. Moreover, Orai1 channels with C-terminal disruption, but not N-terminal truncation, could be gated by fused functional domains of STIM1. Interestingly, the channel activities of Orai1 mutants carrying either an N-terminal or a C-terminal truncation were restored by a methionine mutation at the putative gating hinge, the conserved Gly-98 site in the first transmembrane segment (TM1) of Orai1. Collectively, these results support a stepwise gating mechanism of STIM1-operated Orai1 channels; the initial binding between STIM1 and the C terminus of Orai1 docks STIM1 onto the N terminus of Orai1 to initiate conformational changes of the pore-lining TM1 helix of Orai1, leading to the opening of the channel.

Stroke is a leading cause of long‐lasting disability in humans. However, currently there are still no effective therapies available for promoting stroke recovery. Recent studies have shown that the adult brain has the capacity to regenerate neurons after stroke. Although this neurogenic response may be functionally important for brain repair after injury, the mechanisms underlying stroke‐induced neurogenesis are not known. Caspase‐3 is a major executioner and has been identified as a key mediator of neuronal death in the acute stage of stroke. Recently, however, accumulating data indicate that caspase‐3 also participates in various biological processes that do not cause cell death. Here, we show that cleaved caspase‐3 was increased in newborn neuronal precursor cells (NPCs) in the subventricular zone (SVZ) and the dentate gyrus during the period of stroke recovery, with no evidence of apoptosis. We observed that cleaved caspase‐3 was expressed by NPCs and limited its self‐renewal without triggering apoptosis in cultured NPCs from the SVZ of ischemic mice. Moreover, we revealed that caspase‐3 negatively regulated the proliferation of NPCs through reducing the phosphorylation of Akt. Importantly, we demonstrated that peptide inhibition of caspase‐3 activity significantly promoted the proliferation and migration of SVZ NPCs and resulted in a significant increase in subsequent neuronal regeneration and functional recovery after stroke. Together, our data identify a previously unknown caspase‐3‐dependent mechanism that constrains stroke‐induced endogenous neurogenesis and should revitalize interest in targeting caspase‐3 for treatment of stroke. Stem Cells 2014;32:473–486

Idiopathic primary hyperaldosteronism (IHA) and low-renin essential hypertension (LREH) are common forms of hypertension, characterized by an elevated aldosterone-renin ratio and hypersensitivity to angiotensin II. They are suggested to be 2 states within a disease spectrum that progresses from LREH to IHA as the control of aldosterone production by the renin-angiotensin system is weakened. The mechanism(s) that drives this progression remains unknown. Deletion of Twik-related acid-sensitive K ⁺ channels (TASK) subunits, TASK-1 and TASK-3, in mice (T1T3KO) produces a model of human IHA. Here, we determine the effect of deleting only TASK-3 (T3KO) on the control of aldosterone production and blood pressure. We find that T3KO mice recapitulate key characteristics of human LREH, salt-sensitive hypertension, mild overproduction of aldosterone, decreased plasma-renin concentration with elevated aldosterone:renin ratio, hypersensitivity to endogenous and exogenous angiotensin II, and failure to suppress aldosterone production with dietary sodium loading. The relative differences in levels of aldosterone output and aldosterone:renin ratio and in autonomy of aldosterone production between T1T3KO and T3KO mice are reminiscent of differences in human hypertensive patients with LREH and IHA. Our studies establish a model of LREH and suggest that loss of TASK channel activity may be one mechanism that advances the syndrome of low renin hypertension.

Low voltage-activated (LVA), T-type, calcium channels mediate diverse biological functions and are inhibited by Gβγ dimers, yet the molecular events required for channel inhibition remain unknown. Here, we identify protein kinase A (PKA) as a molecular switch that allows Gβ₂γx dimers to effect voltage-independent inhibition of Ca_v3.2 channels. Inhibition requires phosphorylation of Ser¹¹⁰⁷, a critical serine residue on the II-III loop of the channel pore protein. S1107A prevents inhibition of unitary currents by recombinant Gβ₂γ₂ dimers but does not disrupt dimer binding nor change its specificity. Gβγ dimers released upon receptor activation also require PKA activity for their inhibitory actions. Hence, dopamine inhibition of Ca_v3.2 whole cell current is precluded by Gβγ-scavenger proteins or a peptide that blocks PKA catalytic activity. Fittingly, when used alone at receptor-selective concentrations, D₁ or D₂ agonists do not elicit channel inhibition yet together synergize to inhibit Ca_v3.2 channel currents. We propose that a dual-receptor regulatory mechanism is used by dopamine to control Ca_v3.2 channel activity. This mechanism, for example, would be important in aldosterone producing adrenal glomerulosa cells where channel dysregulation would lead to overproduction of aldosterone and consequent cardiac, renal, and brain target organ damage.