Kir4.1 deletion prevents salt-sensitive hypertension in early streptozotocin-induced diabetic mice via Na + -Cl - cotransporter in the distal convoluted tubule.

OBJECTIVES: Functional impairment of renal sodium handling and blood pressure (BP) homeostasis is an early characteristic manifestation of type 1 diabetes. However, the underlying mechanisms remain unclear. METHODS: Metabolic cages, radio-telemetry, immunoblotting, and electrophysiology were utilized to examine effects of high salt (8% NaCl, HS) intake on Na + /K + balance, BP, Na + -Cl - cotransporter (NCC) function, and basolateral K + channel activity in the distal convoluted tubule (DCT) under diabetic conditions. RESULTS: Improper Na + balance, hypernatremia, and a mild but significant increase in BP were found in streptozotocin (STZ)-induced diabetic mice in response to HS intake for 7 days. Compared to the vehicle, STZ mice showed increased Kir4.1 expression and activity in the DCT, a more negative membrane potential, higher NCC abundance, and enhanced hydrochlorothiazide-induced natriuretic effect. However, HS had no significant effect on basolateral Kir4.1 expression/activity and DCT membrane potential, or NCC activity under diabetic conditions, despite a downregulation in phosphorylated NCC abundance. In contrast, HS significantly downregulated the expression of Na + -H + exchanger 3 (NHE3) and cleaved epithelial sodium channel-γ in STZ mice, despite an increase in NHE3 abundance after STZ treatment. Kir4.1 deletion largely abolished STZ-induced upregulation of NCC expression and prevented BP elevation during HS intake. Interestingly, HS causes severe hypokalemia in STZ-treated kidney-specific Kir4.1 knockout (Ks-Kir4.1 KO) mice and lead to death within a few days, which could be attributed to a higher circulating aldosterone level. CONCLUSIONS: We concluded that Kir4.1 is required for upregulating NCC activity and may be essential for developing salt-sensitive hypertension in early STZ-induced diabetes.

Cardiorenal protective effects of sodium-glucose cotransporter 2 inhibition in combination with angiotensin II type 1 receptor blockade in salt-sensitive Dahl rats.

OBJECTIVE: The kidney plays a central role in regulating the salt sensitivity of blood pressure (BP) by governing sodium excretion and reabsorption via renal sodium transporters. We hypothesized that sodium-glucose cotransporter 2 (SGLT2) inhibition and angiotensin II type 1 receptor (AT1R) blockade can synergistically reduce renal sodium reabsorption by beneficially effects on these transporters, leading to lower BP and ameliorating renal and cardiac damage. METHODS AND RESULTS: Dahl salt-sensitive rats were treated orally for 8weeks with a normal salt diet (0.3% NaCl), a high-salt diet (8% NaCl), high-salt diet with ipragliflozin (0.04%), high-salt diet with losartan (0.05%) or high-salt diet with a combination of ipragliflozin and losartan. The combination treatment significantly reduced BP and increased daily urine sodium excretion compared with losartan or ipragliflozin monotherapy, leading to greater improvement in BP salt sensitivity than ipragliflozin monotherapy. The combination treatment significantly ameliorated glomerulosclerosis and reduced cardiomyocyte hypertrophy compared with losartan or ipragliflozin monotherapy. The protein expression levels of Na+/H+ exchanger isoform 3 (NHE3) and Na+-K+-CI- cotransporter 2 (NKCC2) in the kidney were significantly decreased with losartan monotherapy and combination treatment, but not with ipragliflozin monotherapy. CONCLUSION: Inhibition of SGLT2 in combination with an angiotensin II receptor blocker effectively improved BP salt sensitivity by reducing renal expression levels of sodium transporters including NHE3 and NKCC2, which eventually led to improvement of BP salt sensitivity and cardiorenal protection.

SLC26A3 inhibitor identified in small molecule screen blocks colonic fluid absorption and reduces constipation.

SLC26A3 (downregulated in adenoma; DRA) is a Cl-/anion exchanger expressed in the luminal membrane of intestinal epithelial cells, where it facilitates electroneutral NaCl absorption. SLC26A3 loss of function in humans or mice causes chloride-losing diarrhea. Here, we identified slc26a3 inhibitors in a screen of 50,000 synthetic small molecules done in Fischer rat thyroid (FRT) cells coexpressing slc26a3 and a genetically encoded halide sensor. Structure-activity relationship studies were done on the most potent inhibitor classes identified in the screen: 4,8-dimethylcoumarins and acetamide-thioimidazoles. The dimethylcoumarin DRAinh-A250 fully and reversibly inhibited slc26a3-mediated Cl- exchange with HCO3-, I-, and thiocyanate (SCN-), with an IC50 of ~0.2 µM. DRAinh-A250 did not inhibit the homologous anion exchangers slc26a4 (pendrin) or slc26a6 (PAT-1), nor did it alter activity of other related proteins or intestinal ion channels. In mice, intraluminal DRAinh-A250 blocked fluid absorption in closed colonic loops but not in jejunal loops, while the NHE3 (SLC9A3) inhibitor tenapanor blocked absorption only in the jejunum. Oral DRAinh-A250 and tenapanor comparably reduced signs of constipation in loperamide-treated mice, with additive effects found on coadministration. DRAinh-A250 was also effective in loperamide-treated cystic fibrosis mice. These studies support a major role of slc26a3 in colonic fluid absorption and suggest the therapeutic utility of SLC26A3 inhibition in constipation.