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Angiotensin II (ANG II) increases thiazide-sensitive sodium-chloride cotransporter (NCC) activity both acutely and chronically. ANG II has been implicated as a switch that turns WNK4 from an inhibitor of NCC into an activator of NCC, and ANG II's effect on NCC appears to require WNK4. Chronically, ANG II stimulation of NCC results in an increase in total and phosphorylated NCC, but the role of NCC phosphorylation in acute ANG II actions is unclear. Here, using a mammalian cell model with robust native NCC activity, we corroborate the role that ANG II plays in WNK4 regulation and clarify the role of Ste20-related proline alanine-rich kinase (SPAK)-induced NCC phosphorylation in ANG II action. ANG II was noted to have a biphasic effect on NCC, with a peak increase in NCC activity in the physiologic range of 10-11 M ANG II. This effect was apparent as early as 15 min and remained sustained through 120 min. These changes correlated with significant increases in NCC surface protein expression. Knockdown of WNK4 expression sharply attenuated the effect of ANG II. SPAK knockdown did not affect ANG II action at early time points (15 and 30 min), but it did attenuate the response at 60 min. Correspondingly, NCC phosphorylation did not increase at 15 or 30 min, but increased significantly at 60 min. We therefore conclude that within minutes of an increase in ANG II, NCC is rapidly trafficked to the cell surface in a phosphorylation-independent but WNK4-dependent manner. Then, after 60 min, ANG II induces SPAK-dependent phosphorylation of NCC. [ABSTRACT FROM AUTHOR]

With-no-lysine kinase-1 (WNK1) gene mutations cause familial hyperkalemic hypertension (FHHt), a Mendelian disorder of excessive renal Na+ and K+ retention. Through its catalytic activity, full-length kinase-sufficient WNK1 (L-WNK1) suppresses its paralog, WNK4, thereby upregulating thiazide-sensitive Na-Cl cotransporter (NCC) activity. The predominant renal WNK1 isoform, KS-WNK1, expressed exclusively and at high levels in distal nephron, is a shorter kinase-defective product; the function of KS-WNK1 must therefore be kinase independent. Here, we report a novel role for KS-WNK1 as a dominant-negative regulator of L-WNK1. Na+ transport studies in Xenopus laevis oocytes demonstrate that KS-WNK1 downregulates NCC activity indirectly, by inhibiting L-WNK1. KS-WNK1 also associates with L-WNK1 in protein complexes in oocytes and attenuates L-WNK1 kinase activity in vitro. These observations suggest that KS-WNK1 plays an essential role in the renal molecular switch regulating Na+ and K+ balance; they provide insight into the kidney-specific phenotype of FHHt. [ABSTRACT FROM AUTHOR]

Prenatal factors, especially intrauterine growth retardation, have been shown to correlate with the risk of essential hypertension in adult life, but the mechanisms are unknown. An experimental model of prenatal programming of hypertension in the rat, induced by a maternal low-protein diet during pregnancy, was employed to study the role of renal Na reabsorption in the pathogenesis. The abundance of the apical Na transporter type III Na/H exchanger (NHE3), bumetanide-sensitive Na-K-2Cl cotransporter (BSC1), thiazide-sensitive Na-Cl cotransporter (TSC), and the amiloride-sensitive epithelial Na channel (ENaC) was determined by semiquantitative immunoblotting in kidneys from the offspring at 4 wk of age, before hypertension became manifest. There were no significant differences between the experimental and control rats in the abundance of NHE3 or any of the ENaC subunits. In contrast, the quantity of BSC1 in the experimental group was increased to 302% of control (P < 0.001) and that of TSC to 157% of control (P < 0.05). Determination of specific mRNA levels by ELISA-linked RT-PCR revealed a significantly increased BSC1 mRNA at 1 day (P < 0.01), 4 wk (P < 0.01), and 8 wk (P < 0.001) of age, and a significantly increased TSC mRNA at 4 wk of age (P < 0.05) in the experimental group. The results suggest that prenatal programming of hypertension involves transcriptional upregulation of Na transport in thick ascending limb and distal convoluted tubule. [ABSTRACT FROM AUTHOR]