Of channels and pumps: different ways to boost the aldosterone?

Nocturia and obstructive sleep apnoea

Nocturia, the need to urinate at night, is a common symptom in patients with obstructive sleep apnoea (OSA). Continuous positive airway pressure treatment can reduce nocturia in some patients, but the underlying mechanisms are complex and not fully understood. OSA affects the autonomic nervous system, oxidative stress and endothelial damage. Furthermore, the commonly held theory attributing polyuria to a false signal of cardiac overload and response natriuresis has limitations. A comprehensive approach to the management of nocturia in OSA, considering factors such as comorbidities, medication use, alcohol consumption and lifestyle, is needed. Effective management of nocturia in OSA requires a multidisciplinary approach, and urologists should be aware of the potential effect of OSA on physiology and refer patients for further testing at a sleep centre. In addition to continuous positive airway pressure, other interventions such as oral appliances and surgical obstruction treatment could be beneficial for some patients. Overall, understanding the complex interplay between OSA and nocturia is crucial for optimizing patient outcomes.

Cardiovascular and metabolic characters of KCNJ5 somatic mutations in primary aldosteronism

BACKGROUND

Primary aldosteronism (PA) is the leading cause of curable endocrine hypertension, which is associated with a higher risk of cardiovascular and metabolic insults compared to essential hypertension. Aldosterone-producing adenoma (APA) is a major cause of PA, which can be treated with adrenalectomy. Somatic mutations are the main pathogenesis of aldosterone overproduction in APA, of which KCNJ5 somatic mutations are most common, especially in Asian countries. This article aimed to review the literature on the impacts of KCNJ5 somatic mutations on systemic organ damage.

EVIDENCE ACQUISITION

PubMed literature research using keywords combination, including "aldosterone-producing adenoma," "somatic mutations," "KCNJ5," "organ damage," "cardiovascular," "diastolic function," "metabolic syndrome," "autonomous cortisol secretion," etc.

RESULTS

APA patients with KCNJ5 somatic mutations are generally younger, female, have higher aldosterone levels, lower potassium levels, larger tumor size, and higher hypertension cure rate after adrenalectomy. This review focuses on the cardiovascular and metabolic aspects of KCNJ5 somatic mutations in APA patients, including left ventricular remodeling and diastolic function, abdominal aortic thickness and calcification, arterial stiffness, metabolic syndrome, abdominal adipose tissue, and correlation with autonomous cortisol secretion. Furthermore, we discuss modalities to differentiate the types of mutations before surgery.

CONCLUSION

KCNJ5 somatic mutations in patients with APA had higher left ventricular mass (LVM), more impaired diastolic function, thicker aortic wall, lower incidence of metabolic syndrome, and possibly a lower incidence of concurrent autonomous cortisol secretion, but better improvement in LVM, diastolic function, arterial stiffness, and aortic wall thickness after adrenalectomy compared to patients without KCNJ5 mutations.

Vascular and hormonal interactions in the adrenal gland

Primary aldosteronism is the most common form of secondary arterial hypertension, due to excessive aldosterone production from the adrenal gland. Although somatic mutations have been identified in aldosterone producing adenoma, the exact mechanisms leading to increased cell proliferation and nodule formation remain to be established. One hypothesis is that changes in vascular supply to the adrenal cortex, due to phenomena of atherosclerosis or high blood pressure, may influence the morphology of the adrenal cortex, resulting in a compensatory growth and nodule formation in response to local hypoxia. In this review, we will summarize our knowledge on the mechanisms regulating adrenal cortex development and function, describe adrenal vascularization in normal and pathological conditions and address the mechanisms allowing the cross-talk between the hormonal and vascular components to allow the extreme tissue plasticity of the adrenal cortex in response to endogenous and exogenous stimuli. We will then address recent evidence suggesting a role for alterations in the vascular compartment that could eventually be involved in nodule formation and the development of primary aldosteronism.

Cellular Pathophysiology of Mutant Voltage-Dependent Ca2+ Channel CACNA1H in Primary Aldosteronism

The physiological stimulation of aldosterone production in adrenocortical glomerulosa cells by angiotensin II and high plasma K+ depends on the depolarization of the cell membrane potential and the subsequent Ca2+ influx via voltage-activated Ca2+ channels. Germline mutations of the low-voltage activated T-type Ca2+ channel CACNA1H (Cav3.2) have been found in patients with primary aldosteronism. Here, we investigated the electrophysiology and Ca2+ signaling of adrenal NCI-H295R cells overexpressing CACNA1H wildtype and mutant M1549V in order to understand how mutant CACNA1H alters adrenal cell function. Whole-cell patch-clamp measurements revealed a strong activation of mutant CACNA1H at the resting membrane potential of adrenal cells. Both the expression of wildtype and mutant CACNA1H led to a depolarized membrane potential. In addition, cells expressing mutant CACNA1H developed pronounced action potential-like membrane voltage oscillations. Ca2+ measurements showed an increased basal Ca2+ activity, an altered K+ sensitivity, and abnormal oscillating Ca2+ changes in cells with mutant CACNA1H. In addition, removal of extracellular Na+ reduced CACNA1H current, voltage oscillations, and Ca2+ levels in mutant cells, suggesting a role of the partial Na+ conductance of CACNA1H in cellular pathology. In conclusion, the pathogenesis of stimulus-independent aldosterone production in patients with CACNA1H mutations involves several factors: i) a loss of normal control of the membrane potential, ii) an increased Ca2+ influx at basal conditions, and iii) alterations in sensitivity to extracellular K+ and Na+. Finally, our findings underline the importance of CACNA1H in the control of aldosterone production and support the concept of the glomerulosa cell as an electrical oscillator.

Aldosterone up-regulates voltage-gated potassium currents and NKCC1 protein membrane fractions

Na+-K+-2Cl- Cotransporter (NKCC1) is a protein that aids in the active transport of sodium, potassium, and chloride ions across cell membranes. It has been shown that long-term systemic treatment with aldosterone (ALD) can enhance NKCC1 protein expression and activity in the aging cochlea resulting in improved hearing. In the present work, we used a cell line with confirmed NKCC1 expression to demonstrate that in vitro application of ALD increased outward voltage-gated potassium currents significantly, and simultaneously upregulated whole lysate and membrane portion NKCC1 protein expression. These ALD-induced changes were blocked by applying the mineralocorticoid receptor antagonist eplerenone. However, application of the NKCC1 inhibitor bumetanide or the potassium channel antagonist Tetraethyl ammonium had no effect. In addition, NKKC1 mRNA levels remained stable, indicating that ALD modulates NKCC1 protein expression via the activation of mineralocorticoid receptors and post-transcriptional modifications. Further, in vitro electrophysiology experiments, with ALD in the presence of NKCC1, K+ channel and mineralocorticoid receptor inhibitors, revealed interactions between NKCC1 and outward K+ channels, mediated by a mineralocorticoid receptor-ALD complex. These results provide evidence of the therapeutic potential of ALD for the prevention/treatment of inner ear disorders such as age-related hearing loss.

Region-specific mechanisms of corticosteroid-mediated inotropy in rat cardiomyocytes

Regional differences in ion channel activity in the heart control the sequence of repolarization and may contribute to differences in contraction. Corticosteroids such as aldosterone or corticosterone increase the L-type Ca²⁺ current (I_CaL) in the heart via the mineralocorticoid receptor (MR). Here, we investigate the differential impact of corticosteroid-mediated increase in I_CaL on action potentials (AP), ion currents, intracellular Ca²⁺ handling and contractility in endo- and epicardial myocytes of the rat left ventricle. Dexamethasone led to a similar increase in I_CaL in endocardial and epicardial myocytes, while the K⁺ currents I_to and I_K were unaffected. However, AP duration (APD) and AP-induced Ca²⁺ influx (Q_Ca) significantly increased exclusively in epicardial myocytes, thus abrogating the normal differences between the groups. Dexamethasone increased Ca²⁺ transients, contractility and SERCA activity in both regions, the latter possibly due to a decrease in total phospholamban (PLB) and an increase PLBpThr17. These results suggest that corticosteroids are powerful modulators of I_CaL, Ca²⁺ transients and contractility in both endo- and epicardial myocytes, while APD and Q_Ca are increased in epicardial myocytes only. This indicates that increased I_CaL and SERCA activity rather than Q_Ca are the primary drivers of contractility by adrenocorticoids.

The Effects of Different Calcium Channel Blockers on Aldosterone-Producing Adenoma Cells

Purpose: The aim of this study is to examine the effects of different kinds of calcium channel blockers (CCBs) on primary aldosterone-producing adenoma (APA) mainly with KCNJ5 mutations. Primary cultured APA cells were treated with different calcium channel blockers (L/T type CCB benidipine, T-type CCB mibefradil and L-type CCB nifedipine), and aldosterone secretagogues with or without nifedipine. Aldosterone level, aldosterone synthase (CYP11B2) mRNA expression and cell proliferation were detected. The results showed that all three CCBs significantly inhibit aldosterone secretion and CYP11B2 mRNA expression. Benidipine was relatively more effective than mibefradil or nifedipine. In addition, only mibefradil marginally inhibited cell proliferation. Adrenocorticotropin (ACTH) had a much stronger effect in stimulating aldosterone secretion and promoting cell proliferation from APA's than angiotensin II (ATII). Different from ACTH and ATII, potassium had no effect. Nifedipine inhibited the basal and ACTH-, ATII-elicited aldosterone secretion. Twenty three of 24 APAs had somatic KCNJ5 mutation. In conclusion, benidipine, mibefradil and nifedipine significantly inhibit aldosterone secretion in primary cultured APA cells.

Role of the Renin Angiotensin System in Blood Pressure Allostasis-induced by Severe Food Restriction in Female Fischer rats

Severe food restriction (FR) is associated with blood pressure (BP) and cardiovascular dysfunction. The renin-angiotensin system (RAS) regulates BP and its dysregulation contributes to impaired cardiovascular function. Female Fischer rats were maintained on a control (CT) or severe FR (40% of CT) diet for 14 days. In response to severe FR, BP allostasis was achieved by up-regulating circulating Ang-[1–8] by 1.3-fold through increased angiotensin converting enzyme (ACE) activity and by increasing the expression of AT₁Rs 1.7-fold in mesenteric vessels. Activation of the RAS countered the depressor effect of the severe plasma volume reduction (≥30%). The RAS, however, still underperformed as evidenced by reduced pressor responses to Ang-[1–8] even though AT₁Rs were still responsive to the depressor effects of an AT₁R antagonist. The aldosterone (ALDO) response was also inadequate as no changes in plasma ALDO were observed after the large fall in plasma volume. These findings have implications for individuals who have experienced a period(s) of severe FR (e.g., anorexia nervosa, dieters, natural disasters) and suggests increased activity of the RAS in order to achieve allostasis contributes to the cardiovascular dysfunction associated with inadequate food intake.