Dose-dependent effects of angiotensin-(1–7) on the NHE3 exchanger and [Ca²⁺]_iin in vivo proximal tubules

Abstract

The acute direct action of angiotensin-(1-7) [ANG-(1-7)] on bicarbonate reabsorption (JHCO(3)(-)) was evaluated by stationary microperfusions on in vivo middle proximal tubules in rats using H ion-sensitive microelectrodes. The control JHCO(3)(-) is 2.82 ± 0.078 nmol·cm(-2)·s(-1) (50). ANG-(1-7) (10(-12) or 10(-9) M) in luminally perfused tubules decreases JHCO(3)(-) (36 or 60%, respectively), but ANG-(1-7) (10(-6) M) increases it (80%). A779 increases JHCO(3)(-) (30%) and prevents both the inhibitory and the stimulatory effects of ANG-(1-7) on it. S3226 decreases JHCO(3)(-) (45%) and changes the stimulatory effect of ANG-(1-7) to an inhibitory effect (30%) but does not affect the inhibitory effect of ANG-(1-7). Our results indicate that in the basal condition endogenous ANG-(1-7) inhibits JHCO(3)(-) and that the biphasic dose-dependent effect of ANG-(1-7) on JHCO(3)(-) is mediated by the Mas receptors via the Na(+)/H(+) exchanger 3 (NHE3). The control value of intracellular Ca(2+) concentration ([Ca(2+)](i)), as monitored using fura-2 AM, is 101 ± 2 nM (6), and ANG-(1-7) (10(-12), 10(-9), or 10(-6)M) transiently (3 min) increases it (by 151, 102, or 52%, respectively). A779 increases the [Ca(2+)](i) (25%) but impairs the stimulatory effect of all doses of ANG-(1-7) on it. The use of BAPTA or thapsigargin suggests a correlation between the ANG-(1-7) dose-dependent effects on [Ca(2+)](i) and JHCO(3)(-). Therefore, the interaction of the opposing dose-dependent effects of ANG II and ANG-(1-7) on [Ca(2+)](i) and JHCO(3)(-) may represent an physiological regulatory mechanism of extracellular volume and/or pH changes. However, whether [Ca(2+)](i) modification is an important direct mechanism for NHE3 activation by these peptides or is a side effect of other signaling pathways will require additional studies.

Angiotensin-(1–7) abolishes AGE-induced cellular hypertrophy and myofibroblast transformation via inhibition of ERK1/2

“…It is worth noting that both studies demonstrate that the Ang-(1-7)/Mas antagonist DAL blocked the cellular actions of Ang-(1-7) suggesting the Mas receptor may transduce dose-dependent effects of the peptide. In this regard, de Mello-Aires and colleagues reported dose-dependent biphasic effects of Ang-(1-7) on the proximal tubule NHE3 exchanger that were completely blocked by DAL (8). Ang II also exhibits biphasic effects on sodium reabsorption that are mediated through the AT 1 receptor and multiple signaling pathways, albeit the tubular actions of Ang II are opposite to those of Ang-(1-7) (22).…”

“…Functional links between AGEs, TGF-β and the differential activation of the renal RAS are becoming increasingly evident as well (48). Cao and colleagues find that AGEs (hydoxychloride-treated rat albumin) increased the expression of the precursor protein angiotensinogen, ACE and AT 1 receptors in the NRK-52E cells (8). Chou et al also reported that chronic treatment of NRK-52E cells with high glucose or TGF-β reduced the mRNA and protein expression of ACE2 and the Ang-(1-7)/Mas receptor (12).…”

“…We also found no effect of AT 1 receptor blockade on α-SMA, TGF-β release or chronic ERK1/2 phosphorylation by MGA. Although we did not perform an extensive characterization of the RAS components in these cells; the NRK-52E cells express a complete RAS capable of expressing the active peptides Ang II and Ang-(1-7), as well as their respective receptors and associated signaling pathways (1; 8; 52; 53). It is important to emphasize that the current findings do not imply that RAS inhibition is not beneficial in the treatment of diabetic renal disease, although the current therapeutic regimen of RAS blockade does not abolish or reverse diabetic nephropathy (41).…”

Renin-angiotensin system in the kidney: What is new?

“…Diuretic/natriuretic effects of Ang-(1-7) may also be due to the regulation of Na + reabsorption within the proximal tubule. In vivo and in vitro studies showed that Ang-(1-7) is a potent inhibitor of Na + reabsorption in this nephron segment, acting on different receptors [46][47][48][49] . Ang-(1-7) can bind to distinct receptors and induces different cellular responses depending on the cell type.…”

“…For instance, in distal tubule cell (MDCK), Ang-(1-7) inhibits (Na + + K + )-ATPase activity through the AT1 receptor to stimulate the PI-PLC/PKC signaling pathway [47] , whereas in the proximal tubule, it inhibits Na + -ATPase via the AT2/G(i/o) protein/cGMP/PKG pathway [48] . Moreover, at different concentrations of Ang-(1-7) (10 -12 , 10 -9 , or 10 -6 mol/L) used in intratubular perfusion in the absence or presence of the Mas receptor antagonist (A779) of rat isolated proximal tubules, it was shown that Ang-(1-7) has a biphasic dose-dependent effect on the Na + /H + exchanger mediated by Mas receptor and gave a moderate increase in intracellular Ca 2+ levels ([Ca 2+ ]i) [49] . Increased [Ca 2+ ]i stimulated by Ang-(1-7) also occurred in MDCK cells, but through the AT1 receptor, which in turn stimulated Ca 2+ release from endoplasmic reticulum via the PLC pathway and Ca 2+ influx through PLA2-dependent store-operated Ca 2+ entry [24] .…”