Activation of Angiotensin II Subtype 2 Receptor Induces Catecholamine Release in an Extracellular Ca2+-Dependent Manner through a Decrease of Cyclic Guanosine 3',5'-Monophosphate Production in Cultured Porcine Adrenal Medullary Chromaffin Cells

Abstract

We have previously demonstrated that CGP 42112 (AT(2) agonist > or =1 nM) markedly reduces catecholamine biosynthesis through AT(2), which is the major angiotensin II (AngII) receptor subtype in cultured porcine chromaffin cells. Also, we have shown that CGP 42112 (> or =1 nM) induces a reduction in cGMP production in these cells. The present study showed that AngII reduced cGMP production via AT(2) in a manner similar to that found with CGP 42112. AngII (1 nM) significantly increased catecholamine secretion from cultured porcine adrenal medullary chromaffin cells. The stimulation was significantly inhibited by PD 123319 (AT(2) antagonist). The stimulation was moderately, but significantly, attenuated by CV-11974 (AT(1) antagonist, > or =10 nM), suggesting an involvement of AT(1). Moreover, CGP 42112 (> or =10 nM) markedly increased catecholamine release from these cells. The stimulation by CGP 42112 was abolished by PD 123319, whereas CV-11974 had no effect, indicating that this response is also mediated by AT(2). We further examined whether extracellular Ca(2+) is involved in the stimulatory effect of AT(2) on catecholamine secretion. Removal of external Ca(2+) significantly suppressed either AngII plus CV-11974 (100 nM; which simulates specific AT(2) stimulation) or CGP 42112- induced catecholamine secretion. AngII plus CV-11974 or CGP 42112 caused a sustained increase in intracellular Ca(2+) ([Ca(2+)](i)), as determined in fura-2-loaded chromaffin cells in an extracellular Ca(2+)-dependent manner. In the presence of EGTA, the subsequent addition of AngII with CV-11974 and CGP 42112 did not cause any increase in [Ca(2+)](i) levels. Consistent with this finding, CGP 42112 (10 nM to 1 microM) did not alter inositol triphosphate (IP(3)) production, a messenger for mobilization of Ca(2+) from intracellular storage sites. In addition, the intracellular Ca(2+) chelator 1,2-bis(2-amino-phenoxy)ethane-N,N,N',N'- tetraacetic acid acetoxymethylester (BAPTA) did not affect CGP 42112-induced catecholamine release. We tested whether a decrease in cGMP was the cause of the stimulatory effect of AT(2) on catecholamine secretion. Pretreatment with 8-bromo-cGMP (1 mM) prevented the stimulatory effect of AngII plus CV-11974 and CGP 42112 on both catecholamine secretion and [Ca(2+)](i). When 8-bromo-cGMP was added after application of AngII plus CV-11974 or CGP 42112, [Ca(2+)](i) induced by these agents was gradually reduced toward the baseline values. Similarly, guanylin completely abolished the AngII- plus CV-11974-induced increase in both NE secretion and [Ca(2+)](i). The Ca(2+) channel blockers, nicardipine and omega-conotoxin G VIA, at 1 microM in both cases, were also effective in inhibiting AT(2) stimulation-induced secretion. On the other hand, neither T-type voltage-dependent Ca(2+) channel blockers, flunarizine, nor Ni(2+) affected catecholamine release caused by AT(2) stimulation. These findings demonstrate that AT(2) stimulation induces catecholamine secretion by mobilizing Ca(2+) through voltage-dependent Ca(2+) cha...

Angiotensin II mediates catecholamine and neuropeptide Y secretion in human adrenal chromaffin cells through the AT1 receptor

“…However, the involvement of AT 1 and AT 2 receptors in such effect is also dependent on the animal species studied [6][7][8][9][10][11][12]. It has been shown that cultured porcine chromaffin cells secreted catecholamines in response to an AT 2 agonist [9], whereas other studies have shown that Ang II increases catecholamine release from bovine chromaffin cells through functionally active AT 1 receptors [12]. Interestingly, some investigations reported mixed population of Ang II receptors in adrenal medulla depending on the species studied; for instance, AT 2 receptors accounted for 95% of Ang II binding sites in rat adrenal medulla, and 5% of the remaining binding sites were AT 1 [14].…”

“…It is well established that angiotensin II (Ang II) is able to stimulate catecholamine release from bovine, rat and porcine adrenal chromaffin cells [1][2][3][4][5][6][7]. However, controversy exists about whether AT 1 or AT 2 receptors are involved in this effect in several species [6 -12].…”

Effects of Losartan on Catecholamine Release in the Isolated Rat Adrenal Gland

“…On the other hand, it has been demonstrated that, in cultured porcine chromaffin cells, AT2 stimulation induces CA secretion by mobilizing Ca 2＋ through voltage-dependent Ca 2＋ channels without affecting intracellular pools and that these effects could be mediated by a decrease in cGMP production (Takekoshi et al, 2001). Worck and his colleagues (1998) have also speculated that angiotensin II through binding to both receptor subtypes (both AT1 and AT2) facilitates the sympathoadrenal reflex response by actions at several anatomical levels of the neural pathways involved in the sympathoadrenal reflex response elicited during insulin-induced hypoglycemia in conscious chronically instrumented rats.…”

“…In the present study, losartan, an AT1-selective antagonist inhibited the CA secretory responses by high potassium, a direct membrane depolarizer, as well as by Bay-K-8644, an activator of L-type Ca 2＋ channels, which facilitates the influx of Ca 2＋ into the cells. The observation that AT1-selective antagonist inhibited the CA secretion evoked by Bay-K-8644 was surprising, as Takekoshi et al (2001) have reported that removal of external Ca 2＋ significantly suppressed either AngII plus CV-11974 (AT1 antagonist, 100 nM; which simulates specific AT2 stimulation) or CGP 42112 (AT2 agonist)-induced CA secretion in cultured porcine adrenomedullary chromaffin cells. It is unclear how the blockade of AT1 receptors results in the inhibition of secretion seen in these cells.…”

“…However, it has been shown that AT2 stimulation induces CA secretion in cultured porcine chromaffin cells (Takekoshi et al, 2001). This suggests that AT2 receptors play a role in mediating CA secretion from the adrenal medulla of anesthetized dogs in response to Ang II receptor agonist administration in vivo.…”