Angiotensin II-mediated biphasic regulation of proximal tubular Na⁺/H⁺ exchanger 3 is impaired during oxidative stress

Abstract

Angiotensin (ANG) II via AT1 receptors (AT1Rs) maintains sodium homeostasis by regulating renal sodium transporters including Na(+)/H(+) exchanger 3 (NHE3) in a biphasic manner. Low-ANG II concentration stimulates whereas high concentrations inhibit NHE3 activity. Oxidative stress has been shown to upregulate AT1R function that could modulate the ANG II-mediated NHE3 regulation. This study was designed to identify the signaling pathways responsible for ANG II-mediated biphasic regulation of proximal tubular NHE3 and the effect of oxidative stress on this phenomenon. Male Sprague-Dawley rats were chronically treated with a pro-oxidant L-buthionine sulfoximine (BSO) with and without an antioxidant tempol in tap water for 3 wk. BSO-treated rats exhibited oxidative stress and high blood pressure. At low concentration (1 pM) ANG II increased NHE3 activity in proximal tubules from all animals. However, in BSO-treated rats, the stimulation was more robust and was normalized by tempol treatment. ANG II (1 pM)-mediated NHE3 activation was abolished by AT1R blocker, intracellular Ca(2+) chelator, and inhibitors of phospholipase C (PLC) and Ca(2+)-dependent calmodulin (CaM) but it was insensitive to Giα and protein kinase C inhibitors or AT2R antagonist. A high concentration of ANG II (1 μM) inhibited NHE3 activity in control and tempol-treated rats. However, in BSO-treated rats, ANG II (1 μM) continued to induce NHE3 stimulation. Tempol restored the inhibitory effect of ANG II (1 μM) in BSO-treated rats. The inhibitory effect of ANG II (1 μM) involved AT1R-dependent, cGMP-dependent protein kinase (PKG) activation and was independent of AT2 receptor and nitric oxide signaling. We conclude that ANG II stimulates NHE3 via AT1R-PLC-CaM pathway and inhibits NHE3 by AT1R-PKG activation. Oxidative stress impaired ANG II-mediated NHE3 biphasic response in that stimulation was observed at both high- and low-ANG II concentration.

Elevated Calcium Acutely Regulates Dynamic Interactions of NHERF2 and NHE3 Proteins in Opossum Kidney (OK) Cell Microvilli

“…6 One way to separate these effects appears to be that the effects of the inhibitors of NHE3 can be blocked by PKC antagonists. This is true for adenosine type 1 receptors, serotonin (27), carbachol (31), and ionophores in the presence of NHERF2 and NHERF3 and not for LPA (33), angiotensin (34), and ionophore in the presence of NHERF4. 6 Thus, this ionophore model of Ca 2ϩ -induced NHE3 inhibition, which has been shown to be associated with stimulated endocytosis, is not the same model as our previously reported LPA stimulation of NHE3 activity, in which the elevation in intracellular Ca 2ϩ was necessary for the NHE3 stimulation.…”

“…1) Inhibitors of NHE3, include serotonin (27), carbachol (11, 24 -26), adenosine type 1 receptors (9, 32), and thapsigargin and Ca 2ϩ ionophores, including 4-Br-A23187 in cells expressing NHERF2 or NHERF3 (12,18,28) as used in this study. 2) Stimulators of NHE3 include LPA (32,33), low concentrations of angiotensin II (34), A23187 in the presence of NHERF4 (35), and EGF. 6 One way to separate these effects appears to be that the effects of the inhibitors of NHE3 can be blocked by PKC antagonists.…”

Mechanisms of angiotensin II stimulation of NCC are time-dependent in mDCT15 cells

“…Other dosages ANG II had variable effects, with some demonstrating no significant change in NCC function. A biphasic or bimodal effect has been shown for other ANG II effects in the kidney (2,11,13,22).…”

Traditional and emerging roles for the SLC9 Na+/H+ exchangers

“…Recently significant insights into how the NHERFs and ezrin affect NHE3 activity, the mechanisms underlying angiotensin II mediated activation of the exchanger, the role of SGK signalling and NHE3 lipid interactions on activity have been made [1,149,30,8,9,184,112,68,117,64].…”