Adrenal adaptation in potassium-depleted men: role of progesterone?

GDF15 mediates renal cell plasticity in response to potassium depletion in mice

OBJECTIVE

To understand the mechanisms involved in the response to a low-K+ diet (LK), we investigated the role of the growth factor GDF15 and the ion pump H,K-ATPase type 2 (HKA2) in this process.

METHODS

Male mice of different genotypes (WT, GDF15-KO, and HKA2-KO) were fed an LK diet for different periods of time. We analyzed GDF15 levels, metabolic and physiological parameters, and the cellular composition of collecting ducts.

RESULTS

Mice fed an LK diet showed a 2-4-fold increase in plasma and urine GDF15 levels. Compared to WT mice, GDF15-KO mice rapidly developed hypokalemia due to impaired renal adaptation. This is related to their 1/ inability to increase the number of type A intercalated cells (AIC) and 2/ absence of upregulation of H,K-ATPase type 2 (HKA2), the two processes responsible for K+ retention. Interestingly, we showed that the GDF15-mediated proliferative effect on AIC was dependent on the ErbB2 receptor and required the presence of HKA2. Finally, renal leakage of K+ induced a reduction in muscle mass in GDF15-KO mice fed LK diet.

CONCLUSIONS

In this study, we showed that GDF15 and HKA2 are linked and play a central role in the response to K+ restriction by orchestrating the modification of the cellular composition of the collecting duct.

Renal K+ retention in physiological circumstances: focus on adaptation of the distal nephron and cross-talk with Na+ transport systems

Consumption of salt (NaCl) and potassium (K+) has been completely modified, switching from a rich-K+/low-NaCl diet in the hunter-gatherer population to the opposite in the modern, westernized population. The ability to conserve K+ is crucial to maintain the plasma K+ concentration in a physiological range when dietary K+ intake is decreased. Moreover, a chronic reduction in the K+ intake is correlated with an increased blood pressure, an effect worsened by a high-Na+ diet. The renal adaptation to a low-K+ diet in order to maintain the plasma K+ level in the normal range is complex and interconnected with the mechanisms of the Na+ balance. In this short review, we will recapitulate the general mechanisms allowing the plasma K+ value to remain in the normal range, when there is a necessity to retain K+ (response to low-K+ diet and adaptation to gestation), by focusing on the processes occurring in the most distal part of the nephron. We will particularly outline the mechanisms of K+ reabsorption and discuss the consequences of its absence on the Na+ transport systems and the regulation of the extracellular compartment volume and blood pressure.

Bartter syndrome type III with glomerular dysplasia and chronic kidney disease: A case report

Background

Bartter syndrome (BS) type III is a rare autosomal recessive genetic disease. Its clinical features are polyuria, hypokalemia, hypochloremia, metabolic alkalosis, and hyperreninaemia. A few BS type III can be complicated with chronic kidney disease.

Case presentation

We report a 14-year-old boy with Bartter syndrome caused by a c.1792C > T (p.Q598*) mutation in the CLCNKB gene. He was a no deafness and full-term baby, and he had renal dysplasia and chronic kidney disease (CKD). In addition, we summarize all cases of BS type III complicated with CKD.

Conclusions

We report a case of Bartter syndrome complicated by chronic kidney disease caused by a new mutation of CLCNKB. As we all know, BS type IV is usually combined with chronic kidney disease, and BS type III can also integrate with CKD. We don't find BS type III with glomerular dysplasia in the literature. So renal damage in BS type III is not only FSGS; clinicians must also be aware of glomerular dysplasia.

A mathematical model of potassium homeostasis: Effect of feedforward and feedback controls

Maintaining normal potassium (K+) concentrations in the extra- and intracellular fluid is critical for cell function. K+ homeostasis is achieved by ensuring proper distribution between extra- and intracellular fluid compartments and by matching K+ excretion with intake. The Na+-K+-ATPase pump facilitates K+ uptake into the skeletal muscle, where most K+ is stored. Na+-K+-ATPase activity is stimulated by insulin and aldosterone. The kidneys regulate long term K+ homeostasis by controlling the amount of K+ excreted through urine. Renal handling of K+ is mediated by a number of regulatory mechanisms, including an aldosterone-mediated feedback control, in which high extracellular K+ concentration stimulates aldosterone secretion, which enhances urine K+ excretion, and a gastrointestinal feedforward control mechanism, in which dietary K+ intake increases K+ excretion. Recently, a muscle-kidney cross talk signal has been hypothesized, where the K+ concentration in skeletal muscle cells directly affects urine K+ excretion without changes in extracellular K+ concentration. To understand how these mechanisms coordinate under different K+ challenges, we have developed a compartmental model of whole-body K+ regulation. The model represents the intra- and extracellular fluid compartments in a human (male) as well as a detailed kidney compartment. We included (i) the gastrointestinal feedforward control mechanism, (ii) the effect of insulin and (iii) aldosterone on Na+-K+-ATPase K+ uptake, and (iv) aldosterone stimulation of renal K+ secretion. We used this model to investigate the impact of regulatory mechanisms on K+ homeostasis. Model predictions showed how the regulatory mechanisms synthesize to ensure that the extra- and intracelluller fluid K+ concentrations remain in normal range in times of K+ loading and fasting. Additionally, we predict that without the hypothesized muscle-kidney cross talk signal, the model was unable to predict a return to normal extracellular K+ concentration after a period of high K+ loading or depletion.

Molecular Basis, Diagnostic Challenges and Therapeutic Approaches of Bartter and Gitelman Syndromes: A Primer for Clinicians

Gitelman and Bartter syndromes are rare inherited diseases that belong to the category of renal tubulopathies. The genes associated with these pathologies encode electrolyte transport proteins located in the nephron, particularly in the Distal Convoluted Tubule and Ascending Loop of Henle. Therefore, both syndromes are characterized by alterations in the secretion and reabsorption processes that occur in these regions. Patients suffer from deficiencies in the concentration of electrolytes in the blood and urine, which leads to different systemic consequences related to these salt-wasting processes. The main clinical features of both syndromes are hypokalemia, hypochloremia, metabolic alkalosis, hyperreninemia and hyperaldosteronism. Despite having a different molecular etiology, Gitelman and Bartter syndromes share a relevant number of clinical symptoms, and they have similar therapeutic approaches. The main basis of their treatment consists of electrolytes supplements accompanied by dietary changes. Specifically for Bartter syndrome, the use of non-steroidal anti-inflammatory drugs is also strongly supported. This review aims to address the latest diagnostic challenges and therapeutic approaches, as well as relevant recent research on the biology of the proteins involved in disease. Finally, we highlight several objectives to continue advancing in the characterization of both etiologies.