Accessibility of ENaC extracellular domain central core residues

Dietary sodium sulfate supplementation improves eggshell quality, uterine ion transportation and glycosaminoglycan synthesis in laying hens

OBJECTIVE

This study evaluated the effects of dietary sodium sulfate (Na2SO4) supplementation on eggshell quality, uterine ion transportation, and glycosaminoglycan (GAG) synthesis.

METHODS

A total of 432 48-wk-old Hy-line Brown laying hens were randomly divided into 6 dietary treatments with 8 replicates of 9 birds each. The experimental laying hens were fed the corn-soybean meal diets (containing 0.15% NaCl) supplemented with 0.22%, 0.37%, 0.52%, 0.68%, 0.83%, or 0.99% Na2SO4 for 12 weeks.

RESULTS

Results showed that the eggshell breaking strength and eggshell ratio significantly increased in the 0.68% Na2SO4 group at the end of wk 56 and wk 60 (p<0.05). In addition, eggshell thickness and weight significantly increased in the 0.68% Na2SO4 group at the end of wk 60 (p<0.05). Eggshell calcium content in the 0.68% Na2SO4 group was higher than that of 0.22% and 0.99% groups (p<0.001). The concentrations of K+ and Ca2+ in the uterine fluid were significantly greater in the 0.68% group than in the other groups (p<0.05). Dietary Na2SO4 increased the gene expression of SLC8A1, SCNN1A, ATP1B1, and KCNMA1 quadratically in the uterus (p<0.05), and higher values were observed in 0.68% group. Additionally, the GAG contents of the eggshell, and ATP-sulfurylase, sulfotransferase, chondroitin sulfate, and dermatan sulfate contents of the isthmus increased linearly with the increment of dietary Na2SO4 (p<0.05). There was a remarkable reduction in mammillary knob width, mammillary thickness, and the percentage of the mammillary layer (p<0.05), and an increment in mammillary knob density, effective thickness, and total thickness in the 0.68% group compared with the 0.22% and 0.99% groups (p<0.05).

CONCLUSION

Overall, there was no dose-related difference with the increment of dietary Na2SO4 levels. The addition of 0.68% Na2SO4 in the corn-soybean basal diet (0.15% Cl) regulated uterine ion transport, increased GAG contents of eggshell, and improved eggshell ultrastructure and quality.

Epithelial Na + Channels Function as Extracellular Sensors

The epithelial Na + channel (ENaC) resides on the apical surfaces of specific epithelia in vertebrates and plays a critical role in extracellular fluid homeostasis. Evidence that ENaC senses the external environment emerged well before the molecular identity of the channel was reported three decades ago. This article discusses progress toward elucidating the mechanisms through which specific external factors regulate ENaC function, highlighting insights gained from structural studies of ENaC and related family members. It also reviews our understanding of the role of ENaC regulation by the extracellular environment in physiology and disease. After familiarizing the reader with the channel's physiological roles and structure, we describe the central role protein allostery plays in ENaC's sensitivity to the external environment. We then discuss each of the extracellular factors that directly regulate the channel: proteases, cations and anions, shear stress, and other regulators specific to particular extracellular compartments. For each regulator, we discuss the initial observations that led to discovery, studies investigating molecular mechanism, and the physiological and pathophysiological implications of regulation. © 2024 American Physiological Society. Compr Physiol 14:5407-5447, 2024.

The Role of Ion-Transporting Proteins in Human Disease

This Special Issue focuses on the significance of ion-transporting proteins, such as ion channels and transporters, providing evidence for their significant contribution to bodily and cellular functions via the regulation of signal transduction and ionic environments [...].

Role of epithelial sodium channel-related inflammation in human diseases

The epithelial sodium channel (ENaC) is a heterotrimer and is widely distributed throughout the kidneys, blood vessels, lungs, colons, and many other organs. The basic role of the ENaC is to mediate the entry of Na+ into cells; the ENaC also has an important regulatory function in blood pressure, airway surface liquid (ASL), and endothelial cell function. Aldosterone, serum/glucocorticoid kinase 1 (SGK1), shear stress, and posttranslational modifications can regulate the activity of the ENaC; some ion channels also interact with the ENaC. In recent years, it has been found that the ENaC can lead to immune cell activation, endothelial cell dysfunction, aggravated inflammation involved in high salt-induced hypertension, cystic fibrosis, pseudohypoaldosteronism (PHA), and tumors; some inflammatory cytokines have been reported to have a regulatory role on the ENaC. The ENaC hyperfunction mediates the increase of intracellular Na+, and the elevated exchange of Na+ with Ca2+ leads to an intracellular calcium overload, which is an important mechanism for ENaC-related inflammation. Some of the research on the ENaC is controversial or unclear; we therefore reviewed the progress of studies on the role of ENaC-related inflammation in human diseases and their mechanisms.

Regulation of distal tubule sodium transport: mechanisms and roles in homeostasis and pathophysiology

Regulated Na⁺ transport in the distal nephron is of fundamental importance to fluid and electrolyte homeostasis. Further upstream, Na⁺ is the principal driver of secondary active transport of numerous organic and inorganic solutes. In the distal nephron, Na⁺ continues to play a central role in controlling the body levels and concentrations of a more select group of ions, including K⁺, Ca⁺⁺, Mg⁺⁺, Cl^-, and HCO₃^-, as well as water. Also, of paramount importance are transport mechanisms aimed at controlling the total level of Na⁺ itself in the body, as well as its concentrations in intracellular and extracellular compartments. Over the last several decades, the transporters involved in moving Na⁺ in the distal nephron, and directly or indirectly coupling its movement to that of other ions have been identified, and their interrelationships brought into focus. Just as importantly, the signaling systems and their components-kinases, ubiquitin ligases, phosphatases, transcription factors, and others-have also been identified and many of their actions elucidated. This review will touch on selected aspects of ion transport regulation, and its impact on fluid and electrolyte homeostasis. A particular focus will be on emerging evidence for site-specific regulation of the epithelial sodium channel (ENaC) and its role in both Na⁺ and K⁺ homeostasis. In this context, the critical regulatory roles of aldosterone, the mineralocorticoid receptor (MR), and the kinases SGK1 and mTORC2 will be highlighted. This includes a discussion of the newly established concept that local K⁺ concentrations are involved in the reciprocal regulation of Na⁺-Cl^- cotransporter (NCC) and ENaC activity to adjust renal K⁺ secretion to dietary intake.