Acid loading in vivo and low pH in culture increase angiotensin receptor expression: enhanced ammoniagenic response to angiotensin II

“…Stimulation of tubule formation by SAA was also studied in cultured S1 proximal tubule cells (11,21). The S1 cells were blue; A, D, G, J, M).…”

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Acute-phase response protein serum amyloid A stimulates renal tubule formation: studies in vitro and in vivo

Kelly¹,

Kluve‐Beckerman²,

Dominguez³

2009

“…Most of the studies of renal proximal tubular ammoniagenesis and its adaptive response to acidosis have been carried out in rat (9,33) and in porcine LLC-PK 1 renal epithelial cell lines (8,15). Only few studies were performed in human renal cells.…”

Section: Discussionmentioning

confidence: 99%

Mitochondrial aquaporin-8 in renal proximal tubule cells: evidence for a role in the response to metabolic acidosis

Molinas

Trumper

Marinelli

2012

Mitochondrial ammonia synthesis in proximal tubules and its urinary excretion are key components of the renal response to maintain acid-base balance during metabolic acidosis. Since aquaporin-8 (AQP8) facilitates transport of ammonia and is localized in inner mitochondrial membrane (IMM) of renal proximal cells, we hypothesized that AQP8-facilitated mitochondrial ammonia transport in these cells plays a role in the response to acidosis. We evaluated whether mitochondrial AQP8 (mtAQP8) knockdown by RNA interference is able to impair ammonia excretion in the human renal proximal tubule cell line, HK-2. By RT-PCR and immunoblotting, we found that AQP8 is expressed in these cells and is localized in IMM. HK-2 cells were transfected with short-interfering RNA targeting human AQP8. After 48 h, the levels of mtAQP8 protein decreased by 53% (P < 0.05). mtAQP8 knockdown decreased the rate of ammonia released into culture medium in cells grown at pH 7.4 (-31%, P < 0.05) as well as in cells exposed to acid (-90%, P < 0.05). We also evaluated mtAQP8 protein expression in HK-2 cells exposed to acidic medium. After 48 h, upregulation of mtAQP8 (+74%, P < 0.05) was observed, together with higher ammonia excretion rate (+73%, P < 0.05). In vivo studies in NH(4)Cl-loaded rats showed that mtAQP8 protein expression was also upregulated after 7 days of acidosis in renal cortex (+51%, P < 0.05). These data suggest that mtAQP8 plays an important role in the adaptive response of proximal tubule to acidosis possibly facilitating mitochondrial ammonia transport.

Section: Animalsmentioning

confidence: 99%

“…S1 proximal tubule cells were from a proximal cell line that we originally derived from the S1 segment of a large T antigen transgenic mouse and were found to express AT 1 receptors (19). They were grown to confluence on plastic petri dishes in 50:50 DMEM: Hams F12 medium supplemented with fetal bovine serum (7%) as described before (19). Before the study, the medium was changed to serum-free medium for 24 h, and then the cells were exposed to pH 7.4 or 7.0 (pH was lowered in the pH 7.0 medium by lowering the bicarbonate and raising the chloride concentrations).…”

Section: Animalsmentioning

confidence: 99%

Effects of acid challenges on type 2 angiotensin II receptor-sensitive ammonia production by the proximal tubule

Nagami

Plumer

Beyda

et al. 2014

Self Cite

Angiotensin II (ANG II) acting through its type 1 (AT1) receptor stimulates total ammonia (tNH3) production by the proximal tubule. The present studies explored the role of ANG II type 2 (AT2) receptors in modulating the stimulatory effects of ANG II on tNH3 production. Mouse S2 proximal tubule segments derived from 18-h and 7-day acid-loaded mice, and non-acid-loaded controls were dissected and microperfused in vitro. Adding ANG II to the luminal perfusion solution resulted in different increments in tNH3 production rates in tubules derived from 18-h vs. 7-day acid-loaded mice such that the increase in tNH3 production with ANG II was higher in tubules derived from 18-h acid-loaded mice compared with those derived from control and 7-day acid-loaded mice. Adding the AT2 receptor blocker PD123319 with ANG II increased ANG II-stimulated tNH3 production in S2 segments from control and 7-day acid-loaded mice but not in those from 18-h acid-loaded mice, and this increased effect of PD123319 was associated with higher AT2 receptor protein levels in brush-border membranes. Studies in cultured proximal tubule cells demonstrated that 2-h exposure to pH 7.0 reduced the modulating effect of PD123319 on ANG II-simulated tNH3 production and reduced cell surface AT2 receptor levels. We concluded that AT2 receptors reduce the stimulatory effect of ANG II on proximal tubule tNH3 production and that the time-dependent impact of AT2 receptor blockade on the ANG II-stimulated tNH3 production corresponded to time-dependent changes in AT2 receptor cell surface expression in the proximal tubule.