Abstract. The mechanism underlying epithelial-tomesenchymal transition (EMT) caused by high glucose (HG) stimulation in diabetic nephropathy (DN) remains to be fully elucidated. The present study investigated the effects of HG on EMT and the activity of glycogen synthase kinase 3β (GSK-3β) in podocytes and the kidneys of db/db mice, and assessed the effects of (2'Z, 3'E)-6-bromoindirubin-3'-oxime (BIO), an inhibitor of GSK-3β, on EMT and glomerular injury. The resulting data showed that the activity of GSK-3β was upregulated by HG and downregulated by BIO in the podocytes and the renal cortex. The expression levels of epithelial markers, including nephrin, podocin and synaptopodin, were decreased by HG and increased by BIO, whereas the reverse were true for mesenchymal markers, including α-smooth muscle actin (α-SMA) and fibronectin. The expression levels of β-catenin and Snail, in contrast to current understanding of the Wnt signaling pathway, were increased by HG and decreased by BIO. In addition, expression of the vitamin D receptor (VDR) was decreased by HG and increased by BIO. In conclusion, the present study revealed that the mechanism by which BIO inhibited HG-mediated EMT in podocytes and the renal cortex was primarily due to the VDR. Treatment with BIO protected renal function by maintaining the integrity of the filtration membrane and decreasing UAE, but not by regulating blood glucose. Therefore, GSK-3β may be used as a sensitive biomarker of DN, and its inhibition by BIO may be effective in the treatment of DN.

Aim Cyclosporin A (CsA) is a widely used immunosuppressive drug that causes hypertension and hyperkalemia. Moreover, CsA‐induced stimulation of the thiazide‐sensitive NaCl cotransporter (NCC) in the kidney has been shown to be responsible for the development of hyperkalemic hypertension. In this study, we tested whether CsA induces the activation of NCC by stimulating the basolateral Kir4.1/Kir5.1 channel in the distal convoluted tubule (DCT). Methods Electrophysiology, immunoblotting, metabolic cages, and radio‐telemetry methods were used to examine the effects of CsA on Kir4.1/Kir5.1 activity in the DCT, NCC function, and blood pressure in wild‐type (WT) and kidney‐specific Kir4.1 knockout (KS‐Kir4.1 KO) mice. Results The single‐channel patch clamp experiment demonstrated that CsA stimulated the basolateral 40 pS K+ channel in the DCT. Whole‐cell recording showed that short‐term CsA administration (2 h) not only increased DCT K+ currents but also shifted the K+ current (IK) reversal potential to the negative range (hyperpolarization). Furthermore, CsA administration increased phosphorylated NCC (pNCC) levels and inhibited renal Na+ and K+ excretions in WT mice but not in KS‐Kir4.1 KO mice, suggesting that Kir4.1 is required to mediate CsA effects on NCC function. Finally, long‐term CsA infusion (14 days) increased blood pressure, plasma K+ concentration, and total NCC or pNCC abundance in WT mice, but these effects were blunted in KS‐Kir4.1 KO mice. Conclusion We conclude that CsA stimulates basolateral K+ channel activity in the DCT and that Kir4.1 is essential for CsA‐induced NCC activation and hyperkalemic hypertension.