Pseudo hypoaldosteronism type 1B due to novel deletion mutation in SCNN1A gene

Pseudo hypoaldosteronism type 1B (PHA1B) is a systemic form of salt wasting. Children present after the first week of life with typical symptoms of an adrenal crisis. PHA1B is caused by autosomal recessive homozygous mutations in genes encoding epithelial sodium channels (ENaC) subunits ?, ? and ?. ENaC are widespread and present in renal tubules, airways, colon, sweat and salivary glands. Electrolyte imbalance is significant with severe hyponatremia, hyperkalemia and metabolic acidosis. In early life until approximately one year of age electrolytes remain unstable despite active management but then gradually improve. The mainstay of treatment is high dose salt replacement, sodium bicarbonate and sodium polystyrene therapy. The adequate treatment and monitoring can result in normal physical and psychomotor development. We present a case of PHA1B with severe intractable electrolyte imbalances in neonatal period. The genetic sequence revealed a novel homozygous deletion mutation in exon 4 of the SCNN1A gene (c.942delC, p.N315Tfs*16).

Renal intercalated cells and blood pressure regulation

Type B and non-A, non-B intercalated cells are found within the connecting tubule and the cortical collecting duct. Of these cell types, type B intercalated cells are known to mediate Cl⁻ absorption and HCO₃⁻ secretion largely through pendrin-dependent Cl⁻/HCO₃⁻ exchange. This exchange is stimulated by angiotensin II administration and is also stimulated in models of metabolic alkalosis, for instance after aldosterone or NaHCO₃ administration. In some rodent models, pendrin-mediated HCO₃⁻ secretion modulates acid-base balance. However, the role of pendrin in blood pressure regulation is likely of more physiological or clinical significance. Pendrin regulates blood pressure not only by mediating aldosterone-sensitive Cl⁻ absorption, but also by modulating the aldosterone response for epithelial Na⁺ channel (ENaC)-mediated Na⁺ absorption. Pendrin regulates ENaC through changes in open channel of probability, channel surface density, and channels subunit total protein abundance. Thus, aldosterone stimulates ENaC activity through both direct and indirect effects, the latter occurring through its stimulation of pendrin expression and function. Therefore, pendrin contributes to the aldosterone pressor response. Pendrin may also modulate blood pressure in part through its action in the adrenal medulla, where it modulates the release of catecholamines, or through an indirect effect on vascular contractile force. This review describes how aldosterone and angiotensin II-induced signaling regulate pendrin and the contributory role of pendrin in distal nephron function and blood pressure.

Renal intercalated cells and blood pressure regulation

Type B and non-A, non-B intercalated cells are found within the connecting tubule and the cortical collecting duct. Of these cell types, type B intercalated cells are known to mediate Cl⁻ absorption and HCO₃⁻ secretion largely through pendrin-dependent Cl⁻/HCO₃⁻ exchange. This exchange is stimulated by angiotensin II administration and is also stimulated in models of metabolic alkalosis, for instance after aldosterone or NaHCO₃ administration. In some rodent models, pendrin-mediated HCO₃⁻ secretion modulates acid-base balance. However, the role of pendrin in blood pressure regulation is likely of more physiological or clinical significance. Pendrin regulates blood pressure not only by mediating aldosterone-sensitive Cl⁻ absorption, but also by modulating the aldosterone response for epithelial Na⁺ channel (ENaC)-mediated Na⁺ absorption. Pendrin regulates ENaC through changes in open channel of probability, channel surface density, and channels subunit total protein abundance. Thus, aldosterone stimulates ENaC activity through both direct and indirect effects, the latter occurring through its stimulation of pendrin expression and function. Therefore, pendrin contributes to the aldosterone pressor response. Pendrin may also modulate blood pressure in part through its action in the adrenal medulla, where it modulates the release of catecholamines, or through an indirect effect on vascular contractile force. This review describes how aldosterone and angiotensin II-induced signaling regulate pendrin and the contributory role of pendrin in distal nephron function and blood pressure.

Upregulation of Prostasin in Nasal Polyps

OBJECTIVES/HYPOTHESIS: Prostasin is a protease that activates epithelial sodium channels (ENaC), which mediate Na+ absorption across epithelial surfaces. Human nasal polyps absorb more ENaC-mediated Na+ than normal mucosa. We investigated the expression and distribution of prostasin in normal mucosa and nasal polyp. STUDY DESIGN: This was a controlled, prospective study. METHODS: The distribution patterns and levels of expression of prostasin in normal sinus mucosa and nasal polyps were evaluated using real-time polymerase chain reaction (PCR), immunohistochemical staining and western blotting. RESULTS: Real-time PCR revealed that the mRNA expression of prostasin was higher in nasal polyps than in normal sinus mucosa. The expression of prostasin was faint in immunohistochemical staining of superficial epithelial cells and submucosal glandular epithelial cells of normal sinus mucosa, but was intense in superficial epithelial cells and submucosal glandular epithelial cells in nasal polyps. Inflammatory cells infiltrating into the nasal mucosa also showed prostasin immunoreactivity in nasal polyps. Western blot analysis with prostasin antiserum detected prostasin protein in normal sinus mucosa and nasal polyps. The expression levels of prostasin were increased in nasal polyps compared with normal sinus mucosa. CONCLUSIONS: The levels of expression of prostasin were upregulated in nasal polyps compared to normal sinus mucosa, suggesting a role in the pathogenesis of nasal polyps. However, the exact pathophysiologic function of prostasin in nasal epithelium warrants further investigation.

Autonomic Neural Regulation of Sodium Transporters and Water Channels in Rat Submandibular Gland

The present study was undertaken to explore the role of autonomic nerves in the regulation of sodium transporters and water channels in the salivary gland. Rats were denervated of their sympathetic or parasympathetic nerves to the submandibular gland. One week later, the expression of Na,K-ATPase, epithelial sodium channels (ENaC), and aquaporins (AQP) was examined in the denervated and contralateral glands. The sympathetic denervation slightly but significantly decreased the expression of alpha1 subunit of Na,K-ATPase, whereas the parasympathetic denervation increased it. The expression of alpha-subunit of ENaC was significantly increased in both the denervated and contralateral glands either by the sympathetic or parasympathetic denervation. The sympathetic denervation significantly increased the expression of AQP5 in both the denervated and contralateral glands, whereas the parasympathetic denervation decreased it. It is suggested that the autonomic nerves have a tonic effect on the regulation of sodium transporters and AQP water channels in the salivary gland.