Regulation of the Na(+)-K(+)-2Cl(-) cotransporter by cGMP/cGMP-dependent protein kinase I after furosemide administration

Anatomophysiology of the Henle's Loop: Emphasis on the Thick Ascending Limb

The loop of Henle plays a variety of important physiological roles through the concerted actions of ion transport systems in both its apical and basolateral membranes. It is involved most notably in extracellular fluid volume and blood pressure regulation as well as Ca²⁺ , Mg²⁺ , and acid-base homeostasis because of its ability to reclaim a large fraction of the ultrafiltered solute load. This nephron segment is also involved in urinary concentration by energizing several of the steps that are required to generate a gradient of increasing osmolality from cortex to medulla. Another important role of the loop of Henle is to sustain a process known as tubuloglomerular feedback through the presence of specialized renal tubular cells that lie next to the juxtaglomerular arterioles. This article aims at describing these physiological roles and at discussing a number of the molecular mechanisms involved. It will also report on novel findings and uncertainties regarding the realization of certain processes and on the pathophysiological consequences of perturbed salt handling by the thick ascending limb of the loop of Henle. Since its discovery 150 years ago, the loop of Henle has remained in the spotlight and is now generating further interest because of its role in the renal-sparing effect of SGLT2 inhibitors. © 2022 American Physiological Society. Compr Physiol 12:1-21, 2022.

Vascular control of kidney epithelial transporters

A major pathway in hypertension pathogenesis involves direct activation of ANG II type 1 (AT1) receptors in the kidney, stimulating Na+ reabsorption. AT1 receptors in tubular epithelia control expression and stimulation of Na+ transporters and channels. Recently, we found reduced blood pressure and enhanced natriuresis in mice with cell-specific deletion of AT1 receptors in smooth muscle (SMKO mice). Although impaired vasoconstriction and preserved renal blood flow might contribute to exaggerated urinary Na+ excretion in SMKO mice, we considered whether alterations in Na+ transporter expression might also play a role; therefore, we carried out proteomic analysis of key Na+ transporters and associated proteins. Here, we show that levels of Na+-K+-2Cl- cotransporter isoform 2 (NKCC2) and Na+/H+ exchanger isoform 3 (NHE3) are reduced at baseline in SMKO mice, accompanied by attenuated natriuretic and diuretic responses to furosemide. During ANG II hypertension, we found widespread remodeling of transporter expression in wild-type mice with significant increases in the levels of total NaCl cotransporter, phosphorylated NaCl cotransporter (Ser71), and phosphorylated NKCC2, along with the cleaved, activated forms of the α- and γ-epithelial Na+ channel. However, the increases in α- and γ-epithelial Na+ channel with ANG II were substantially attenuated in SMKO mice. This was accompanied by a reduced natriuretic response to amiloride. Thus, enhanced urinary Na+ excretion observed after cell-specific deletion of AT1 receptors from smooth muscle cells is associated with altered Na+ transporter abundance across epithelia in multiple nephron segments. These findings suggest a system of vascular-epithelial in the kidney, modulating the expression of Na+ transporters and contributing to the regulation of pressure natriuresis.NEW & NOTEWORTHY The use of drugs to block the renin-angiotensin system to reduce blood pressure is common. However, the precise mechanism for how these medications control blood pressure is incompletely understood. Here, we show that mice lacking angiotensin receptors specifically in smooth muscle cells lead to alternation in tubular transporter amount and function. Thus, demonstrating the importance of vascular-tubular cross talk in the control of blood pressure.

Crustacean hyperglycemic hormone (CHH) regulates the ammonia excretion and metabolism in white shrimp, Litopenaeus vannamei under ammonia-N stress

To understand the adaptation of Litopenaeus vannamei to high environmental ammonia-N, RNA interference was used to investigate the function of crustacean hyperglycemic hormone (CHH) in the physiological process of neuroendocrine signaling transduction, and ammonia excretion and metabolism. The shrimp were exposed to 25 mg/L NH₄Cl and injected with 20 μg/shrimp CHH dsRNA for 72 h. The results showed that hemolymph ammonia content increased under ammonia-N stress and further increased after CHH knockdown, suggesting that CHH can promote ammonia excretion. Moreover, after CHH knockdown, the levels of CHH, DA, and Wnts decreased significantly, the expression of receptor GC, DA1R, Frizzled and LRP 5/6 also decreased, while DA4R increased remarkably. Moreover, PKA and PKG decreased, while PKC markedly increased, and nuclear transcription factors (CREB and TCF) as well as effector proteins (β-catenin, FXYD2, and 14-3-3) were significantly downregulated. Furthermore, ammonia transporters Na⁺/K⁺-ATPase (NKA), K⁺channel, Rh protein, AQP, V-ATPase, and VAMP decreased significantly, while Na⁺/H⁺ exchangers (NHE) and Na⁺/K⁺/2Cl^- cotransporter (NKCC) increased significantly. These results suggest that CHH regulates ammonia excretion in three ways: 1) by mainly regulating ion channels via PKA, PKC, and PKG signaling pathways; 2) by activating related proteins primarily through Wnt signaling pathway; and 3) by exocytosis, mostly induced by the PKA signaling pathway. In addition, the levels of Gln, uric acid, and urea increased in accordance with the activities of GDH/GS, XDH, and arginase, respectively, suggesting that ammonia excretion was inhibited but ammonia metabolism was slightly enhanced. This study deepens our understanding of the mechanism by which crustaceans respond to high environmental ammonia-N.

Differences in renal BMAL1 contribution to Na+ homeostasis and blood pressure control in male and female mice

The renal circadian clock has a major influence on the function of the kidney. Aryl hydrocarbon receptor nuclear translocator-like protein 1 [ARNTL; also known as brain and muscle ARNT-like 1 (BMAL1)] is a core clock protein and transcription factor that regulates the expression of nearly half of all genes. Using male and female kidney-specific cadherin BMAL1 knockout (KS-BMAL1 KO) mice, we examined the role of renal distal segment BMAL1 in blood pressure control and solute handling. We confirmed that this mouse model does not express BMAL1 in thick ascending limb, distal convoluted tubule, and collecting duct cells, which are the final locations for solute and fluid regulation. Male KS-BMAL1 KO mice displayed a substantially lower basal systolic blood pressure compared with littermate control mice, yet their circadian rhythm in pressure remained unchanged [male control mice: 127 ± 0.7 mmHg (n = 4) vs. male KS-BMAL KO mice: 119 ± 2.3 mmHg (n = 5), P < 0.05]. Female mice, however, did not display a genotype difference in basal systolic blood pressure [female control mice: 120 ± 1.6 mmHg (n = 5) vs. female KS-BMAL1 KO mice: 119 ± 1.5 mmHg (n = 7), P = 0.4]. In addition, male KS-BMAL1 KO mice had less Na+ retention compared with control mice in response to a K+-restricted diet (15% less following 5 days of treatment). However, there was no genotype difference in Na+ handling after a K+-restricted diet in female mice. Furthermore, there was evidence indicating a sex-specific response to K+ restriction where female mice reabsorbed less Na+ in response to this dietary challenge compared with male mice. We propose that BMAL1 in the distal nephron and collecting duct contributes to blood pressure regulation and Na+ handling in a sex-specific manner.

Complex Role for E-Prostanoid 4 Receptors in Hypertension

Background Prostaglandin E2 ( PGE 2) is a major prostanoid with multiple actions that potentially affect blood pressure ( BP ). PGE 2 acts through 4 distinct E-prostanoid ( EP ) receptor isoforms: EP 1 to EP 4. The EP 4 receptor ( EP 4R) promotes PGE 2-dependent vasodilation, but its role in the pathogenesis of hypertension is not clear. Methods and Results To address this issue, we studied mice after temporal- and cell-specific deletion of EP 4R. First, using a mouse line with loss of EP 4 expression induced universally after birth, we confirm that EP 4R mediates a major portion of the acute vasodilatory effects of infused PGE 2. In addition, EP 4 contributes to control of resting BP , which was increased by 5±1 mm Hg in animals with generalized deficiency of this receptor. We also show that EP 4 is critical for limiting elevations in BP caused by high salt feeding and long-term infusion of angiotensin II . To more precisely identify the mechanism for these actions, we generated mice in which EP 4R loss is induced after birth and is limited to smooth muscle. In these mice, acute PGE 2-dependent vasodilation was attenuated, indicating that this response is mediated by EP 4R in vascular smooth muscle cells. However, absence of EP 4R only in this vascular compartment had a paradoxical effect of lowering resting BP , whereas the protective effect of EP 4R on limiting angiotensin II-dependent hypertension was unaffected. Conclusions Taken together, our findings support a complex role for EP 4R in regulation of BP and in hypertension, which appears to involve actions of the EP 4R in tissues beyond vascular smooth muscle cells.