Porcine Adrenal Medullary Chromaffin Research Articles

Protein kinase Cβ deficiency attenuates obesity syndrome of ob/ob mice by promoting white adipose tissue remodeling

To explore the role of leptin in PKCβ action and to determine the protective potential of PKCβ deficiency on profound obesity, double knockout (DBKO) mice lacking PKCβ and ob genes were created, and key parameters of metabolism and body composition were studied. DBKO mice had similar caloric intake as ob/ob mice but showed significantly reduced body fat content, improved glucose metabolism, and elevated body temperature. DBKO mice were resistant to high-fat diet-induced obesity. Moreover, PKCβ deficiency increased β-adrenergic signaling by inducing expression of β1- and β3-adrenergic receptors (β-ARs) in white adipose tissue (WAT) of ob/ob mice. Accordingly, p38(MAPK) activation and expression of PGC-1α and UCP-1 were increased in WAT of DBKO mice. Consistent with results of in vivo studies, inhibition of PKCβ in WAT explants from ob/ob mice also increased expression of above β-ARs. In contrast, induction of PGC-1α and UCP-1 expression in brown adipose tissue of DBKO mice was not accompanied by changes in the expression of these β-ARs. Collectively, these findings suggest that PKCβ deficiency may prevent genetic obesity, in part, by remodeling the catabolic function of adipose tissues through β-ARs dependent and independent mechanisms.

Reduction of Allodynia by Intrathecal Transplantation of Microencapsulated Porcine Chromaffin Cells

Bovine chromaffin cells (BCCs) are well known to have analgesic effect to reduce acute or chronic pain when transplanted in the subarachnoid space and have been considered as an alternative therapy for pain management. However, due to recent concerns over risks associated with prion transmission, porcine tissue is considered to be an alternate xenogeneic source for clinical use. In the present study, we investigated whether microencapsulated porcine adrenal medullary chromaffin cells (PCCs) also have analgesic effect to reduce allodynia caused by neuropathic pain in chronic constriction injury model of rat. PCCs were isolated from a porcine adrenal medulla and then microencapsulated with alginate and poly. In in vitro tests, the microencapsulated PCCs were investigated whether they have an ability to release catecholamines responding to nicotine stimulation. The levels of catecholamines released from the microencapsulated PCCs were significantly higher than from microencapsulated BCCs. In addition, the microencapsulated PCCs released catecholamines and met-enkephalin responding to cerebral spinal fluid (CSF) retrieved from a neuropathic pain model. In in vivo tests, implantation of microencapsulated PCCs reduced both mechanical and cold allodynia in chronic constriction injury model of a rat whereas the microencapsulated BCCs reduced only cold allodynia under the same conditions. The injection of antagonist of opioid peptides reversed the reduction of cold allodynia in microencapsulated PCC-received animal. The levels of catecholamines in the CSF of rats after implantation of microencapsulated PCCs were significantly higher than in the control group. These data suggest that microencapsulated PCCs may be another effective source for the treatment of neuropathic pain.

Pituitary adenylate cyclase-activating polypeptide induces gene expression of the catecholamine synthesizing enzymes, tyrosine hydroxylase, and dopamine beta-hydroxylase in cultured porcine adrenal medullary chromaffin cells.

Pituitary adenylate cyclase-activating polypeptide induces gene expression of the catecholamine synthesizing enzymes, tyrosine hydroxylase, and dopamine beta-hydroxylase in cultured porcine adrenal medullary chromaffin cells.

Angiotensin II type 2 receptor counter-regulates type 1 receptor in catecholamine synthesis in cultured porcine adrenal medullary chromaffin cells.

We previously showed that CGP 42112 (an angiotensin type 2 [AT(2)] agonist) markedly reduces catecholamine biosynthesis by decreasing cGMP production mediated by AT(2), a subtype of Ang II receptor that is dominantly expressed in cultured porcine chromaffin cells. To elucidate the relationship of the 2 types of Ang II receptors, angiotensin type 1 (AT(1)) and AT(2), in the synthesis of catecholamine in adrenal medullary cells, we have examined the effect of Ang II plus CV-11974 (an AT(1) antagonist that selectively simulates AT(2) stimulation) and the effect of Ang II plus PD 123319 (an AT(2) antagonist that selectively simulates AT(1) stimulation) on catecholamine synthesis. We found that Ang II reduced cGMP production via AT(2), in a similar manner to that found with CGP 42112. Stimulation of AT(1) significantly upregulated protein kinase C activity. Tyrosine hydroxylase (TH) is a rate-limiting enzyme involved in the biosynthesis of catecholamine, and this catecholamine synthesis depends both on TH enzyme activity and on the levels of TH protein after TH gene transcription. We found that AT(2) stimulation significantly inhibited TH enzyme activity, whereas AT(1) stimulation significantly upregulated TH enzyme activity. The stimulatory effect of AT(1) was completely inhibited by Ro-32-0432 (a protein kinase C inhibitor) and PD 98059 (a MAP kinase kinase-1 [MEK-1] inhibitor). Pretreatment of cells with either 8-Br-cGMP (a membrane-permeable cGMP analog) or Zaprinast (a phosphodiesterase inhibitor) abolished the inhibitory effect of AT(2) on TH enzyme activity, indicating that the stimulatory effect of AT(2) may be mediated through a reduction in cGMP concentration. Similar to the effect on TH enzyme activity, AT(2) stimulation significantly reduced TH mRNA and protein levels and net catecholamine content below basal levels, whereas AT(1) stimulation increased them. We confirmed these findings by gel mobility shift assay. Our results show that stimulation of AT(2) reduces catecholamine biosynthesis via a decrease in cGMP levels. In contrast, stimulation of AT(1) stimulates catecholamine biosynthesis through activation of PKC. Thus, we conclude that AT(1) and AT(2) have counter-regulatory roles in the synthesis of catecholamine in adrenal medullary chromaffin cells.

Activation of angiotensin II subtype 2 receptor induces catecholamine release in an extracellular Ca(2+)-dependent manner through a decrease of cyclic guanosine 3',5'-monophosphate production in cultured porcine adrenal medullary chromaffin Cells.

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+) channels without affecting intracellular pools and that these effects could be mediated by a decrease in cGMP production.

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

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

Ca2+ Mobilization, Tyrosine Hydroxylase Activity, and Signaling Mechanisms in Cultured Porcine Adrenal Medullary Chromaffin Cells: Effects of Leptin

Ca2+ Mobilization, Tyrosine Hydroxylase Activity, and Signaling Mechanisms in Cultured Porcine Adrenal Medullary Chromaffin Cells: Effects of Leptin

Ca(2+) mobilization, tyrosine hydroxylase activity, and signaling mechanisms in cultured porcine adrenal medullary chromaffin cells: effects of leptin.

Leptin acts as a satiety factor, but there is also evidence that it affects energy expenditure. Leptin's effects are mediated by its receptors, which function as activators of a Janus family of tyrosine kinases-signal transducer and activator of transcription (JAK-STAT) pathway. We have previously shown that murine recombinant leptin markedly induces both the release of catecholamine and tyrosine hydroxylase (TH) (rate-limiting enzyme in the biosynthesis of catecholamine)-messenger RNA (mRNA) levels, probably through Ob-Rb expressed in cultured porcine chromaffin cells. In the present study, we examined the effect of leptin on Ca(2+) mobilization, TH enzyme activity, and signaling. Ca(2+) channel blockers, nicardipine and omega-Conotoxin GVIA, each at 1 microM, were effective in inhibiting leptin-induced catecholamine secretion. When intracellular Ca(2+) ([Ca(2+)](i)) was measured in fura 2-loaded chromaffin cells, leptin was found to cause a sustained increase of Ca(2+) by mobilizing Ca(2+) from both extra- and intracellular pools. Additionally, leptin significantly stimulated inositol 1.4.5-triphosphate IP(3) production in a dose-dependent manner. TH-activity is regulated by both TH enzyme activity and increased TH-mRNA levels accompanied by increased TH protein synthesis. Leptin (>/=1 nM) significantly stimulated TH enzyme activity and increased the TH protein level, indicating that it stimulates catecholamine biosynthesis. In addition, removal of external Ca(2+) completely inhibited leptin (100 nM)-induced TH enzyme activity. Leptin (>/=1 nM) caused an increase in the activity of mitogen-activated protein kinases (MAPKs) that was accompanied by increased phosphorylation of STAT-3 and -5, but not STAT-1. Moreover, MAPK activity evoked by leptin(100 nM) and TH-mRNA caused by leptin (10 nM) were inhibited by 50 and 30 microM of PD-98059 (the MAP kinase kinase-1 inhibitor), respectively. These findings indicate that leptin activates voltage-dependent Ca(2+) channels (VDCC), presumably L-type and N-type Ca(2+) channels, as well as phospholipase C, and suggest that leptin-induced catecholamine secretion is mainly mediated by activation of VDCC. In addition, leptin stimulates the JAK-STAT pathway as well as increasing the levels of TH-mRNA levels through the MAPK pathway in porcine chromaffin cells.

Modulation of stimulus-secretion coupling in porcine adrenal chromaffin cells by receptor-mediated increases in protein kinase C activity

Catecholamine (CAT) secretion by adrenal chromaffin cells is primarily triggered by nicotinic receptor-dependent increases in cytosolic Ca2+. The principal aim of the present study was to determine whether pituitary adenylate cyclase activating peptide (PACAP), which is coreleased with acetylcholine from the splanchnic nerve, can modulate nicotinic receptor-dependent Ca2+ signaling and catecholamine secretion in porcine adrenal medullary chromaffin (PAMC) cells. Activation of protein kinase C (PKC) with phorbol myristate acetate (PMA) dose- and time-dependently inhibited nicotine (NIC)-induced Ca2+ transients. At 100 nM PMA, peak Ca2+ levels were reduced by 27% ± 2% (P < 0.05) and 41% ± 3% (P < 0.05) after 10 and 20 min exposure, respectively. The inhibitory effects of PMA were significantly reduced by preincubation with the PKC inhibitor staurosporine. KCl-induced Ca2+ transients were also reduced by 20 min PMA treatment (Δ −27% ± 4%; P < 0.05), suggesting that PKC affects voltage-gated Ca2+ channel activity. Pretreatment with PACAP also resulted in both time- and concentration-dependent suppression of Ca2+ transients. After 20 min exposure to 1 μM PACAP, NIC- and KCl-induced transients were reduced by 36% ± 5% (P < 0.05) and 51% ± 6% (P < 0.05), respectively. These effects could also be prevented by staurosporine pretreatment. NIC-induced CAT secretion was significantly reduced by pretreatment with both PMA (Δ −56% ± 2%; P < 0.05) and PACAP (Δ−53% ± 7%; P < 0.05). This suppressive effect on secretion could be prevented by pretreatment with staurosporine. These data suggest that, in addition to having direct stimulatory effects on catecholamine synthesis and secretion, PACAP can also negatively modulate nicotinic receptor-dependent Ca2+ signaling and secretion in PAMC cells. J. Neurosci. Res. 59:760–766, 2000 © 2000 Wiley-Liss, Inc.

Modulation of stimulus-secretion coupling in porcine adrenal chromaffin cells by receptor-mediated increases in protein kinase C activity.

Catecholamine (CAT) secretion by adrenal chromaffin cells is primarily triggered by nicotinic receptor-dependent increases in cytosolic Ca(2+). The principal aim of the present study was to determine whether pituitary adenylate cyclase activating peptide (PACAP), which is coreleased with acetylcholine from the splanchnic nerve, can modulate nicotinic receptor-dependent Ca(2+) signaling and catecholamine secretion in porcine adrenal medullary chromaffin (PAMC) cells. Activation of protein kinase C (PKC) with phorbol myristate acetate (PMA) dose- and time-dependently inhibited nicotine (NIC)-induced Ca(2+) transients. At 100 nM PMA, peak Ca(2+) levels were reduced by 27% +/- 2% (P < 0.05) and 41% +/- 3% (P < 0. 05) after 10 and 20 min exposure, respectively. The inhibitory effects of PMA were significantly reduced by preincubation with the PKC inhibitor staurosporine. KCl-induced Ca(2+) transients were also reduced by 20 min PMA treatment (Delta -27% +/- 4%; P < 0.05), suggesting that PKC affects voltage-gated Ca(2+) channel activity. Pretreatment with PACAP also resulted in both time- and concentration-dependent suppression of Ca(2+) transients. After 20 min exposure to 1 microM PACAP, NIC- and KCl-induced transients were reduced by 36% +/- 5% (P < 0.05) and 51% +/- 6% (P < 0.05), respectively. These effects could also be prevented by staurosporine pretreatment. NIC-induced CAT secretion was significantly reduced by pretreatment with both PMA (Delta -56% +/- 2%; P < 0.05) and PACAP (Delta-53% +/- 7%; P < 0.05). This suppressive effect on secretion could be prevented by pretreatment with staurosporine. These data suggest that, in addition to having direct stimulatory effects on catecholamine synthesis and secretion, PACAP can also negatively modulate nicotinic receptor-dependent Ca(2+) signaling and secretion in PAMC cells.

Stimulus‐secretion coupling in porcine adrenal chromaffin cells: Acute effects of glucocorticoids

Recent studies from this laboratory have established that long-term exposure (48 hr) to glucocorticoids can modulate voltage-gated Ca2+ channel activity and subsequent intracellular Ca2+ transients in porcine adrenal medullary chromaffin (PAMC) cells maintained in primary culture. Consistent with many steroid hormone-mediated responses, this chronic effect of glucocorticoids probably involves increased gene expression and protein synthesis. However, there is now considerable evidence to suggest that steroids can also elicit acute, non-genomic effects. The aim of the present study was to determine whether acute exposure to glucocorticoids also affects nicotinic receptor-dependent catecholamine (CAT) secretion and Ca2+ signaling in PAMC cells. Acute exposure to dexamethasone (DEX) dose-dependently attenuated the degree of nicotine (NIC)-induced CAT secretion, as well as the amplitude of NIC-induced intracellular Ca2+ transients. Significant inhibition of CAT secretion occurred immediately upon addition of DEX, reached maximal levels within 5 min of exposure to DEX, and was rapidly reversible after steroid washout. The endogenous porcine glucocorticoid cortisol elicited similar effects. In contrast, DEX had no significant effect on KCl-induced CAT secretion or intracellular Ca2+ transients. These data demonstrate that acute exposure to glucocorticoids can modulate stimulus-secretion coupling in PAMC cells and suggest that the primary site of action is the nicotinic receptor. J. Neurosci. Res. 57:643–650, 1999. © 1999 Wiley-Liss, Inc.

Stimulus-secretion coupling in porcine adrenal chromaffin cells: Acute effects of glucocorticoids

Recent studies from this laboratory have established that long-term exposure (48 hr) to glucocorticoids can modulate voltage-gated Ca(2+) channel activity and subsequent intracellular Ca(2+) transients in porcine adrenal medullary chromaffin (PAMC) cells maintained in primary culture. Consistent with many steroid hormone-mediated responses, this chronic effect of glucocorticoids probably involves increased gene expression and protein synthesis. However, there is now considerable evidence to suggest that steroids can also elicit acute, non-genomic effects. The aim of the present study was to determine whether acute exposure to glucocorticoids also affects nicotinic receptor-dependent catecholamine (CAT) secretion and Ca(2+) signaling in PAMC cells. Acute exposure to dexamethasone (DEX) dose-dependently attenuated the degree of nicotine (NIC)-induced CAT secretion, as well as the amplitude of NIC-induced intracellular Ca(2+) transients. Significant inhibition of CAT secretion occurred immediately upon addition of DEX, reached maximal levels within 5 min of exposure to DEX, and was rapidly reversible after steroid washout. The endogenous porcine glucocorticoid cortisol elicited similar effects. In contrast, DEX had no significant effect on KCl-induced CAT secretion or intracellular Ca(2+) transients. These data demonstrate that acute exposure to glucocorticoids can modulate stimulus-secretion coupling in PAMC cells and suggest that the primary site of action is the nicotinic receptor.

Leptin Directly Stimulates Catecholamine Secretion and Synthesis in Cultured Porcine Adrenal Medullary Chromaffin Cells

Leptin, a protein encoded by the ob gene, is an adipose tissue-derived signaling factor involved in body weight homeostasis. The hypothalamus is a major site of central action for leptin. However, mounting evidence indicates expression of leptin receptor mRNA in various peripheral organs including the adrenal medulla. Therefore, we investigated the effects of leptin on catecholamine secretion and synthesis in cultured porcine adrenal medullary chromaffin cells. We initially confirmed the expression of leptin receptor (Ob-Rb) mRNA in cultured porcine adrenal medullary cells. Murine recombinant leptin (≧50 nM) strongly induced the release of both epinephrine (E) and norepinephrine (NE) from chromaffin cells. Removal of external Ca2+ significantly suppressed these effects. Also, leptin (≧1 nM) enhanced nicotine-induced increases in E- and NE. Leptin (1, 10, 100 nM) significantly increased tyrosine hydroxylase (TH) (a rate-limiting enzyme in the biosynthesis of catecholamine) mRNA levels in a concentration-dependent manner. Furthermore, leptin (1, 10, 100 nM) significantly induced increases in cAMP levels, suggesting that the stimulatory effects on TH mRNA are mediated, at least in part, by the cAMP/protein kinase A pathway. These results indicate that leptin directly stimulates catecholamine release and synthesis, which in turn may potentiate the anti-obesity effects of leptin.

Stimulus-secretion coupling in porcine adrenal chromaffin cells: Effect of dexamethasone

Recent studies from this laboratory established that dexamethasone (DEX) potentiates Ca2+ current via voltage-gated Ca2+ channels (VGCC), and as a consequence potentiates agonist-induced cytosolic Ca2+ transients in rat adrenal chromaffin cells. The present study examined whether DEX can also modulate VGCC activity and agonist-induced cytosolic Ca2+ transients in porcine adrenal medullary chromaffin (PAMC) cells, and if so whether this results in alterations in catecholamine secretion. Forty-eight-hr exposure to 1 microM DEX significantly increased peak Ca2+ current (delta + 138%; n = 6; P < 0.05) in PAMC cells. DEX treatment also significantly potentiated the increase in cytosolic Ca2+ in response to membrane depolarization with KCl (delta + 20%; n = 29; P < 0.05), but did not affect the amplitude of Ca2+ transients elicited by nicotine or acetylcholine. Despite the potentiation of intracellular Ca2+, DEX treatment had no effect on KCl-induced secretion of either norepinephrine or epinephrine. These data demonstrate that as in the rat chromaffin cell, DEX can also increase VGCC activity in PAMC cells. However, the subsequent potentiation of selected agonist-induced increases in intracellular Ca2+ does not appear to be sufficient to alter catecholamine secretion.

Pituitary adenylate cyclase-activating polypeptide induces gene expression of the catecholamine synthesizing enzymes, tyrosine hydroxylase and dopamine β hydroxylase, through 3′, 5′-cyclic adenosine monophosphate- and protein kinase C-dependent mechanisms in cultured porcine adrenal medullary chromaffin cells

Pituitary adenylate cyclase-activating polypeptide (PACAP), a potent stimulant of catecholamine secretion, increased catecholamine production in cultured porcine adrenal medullary chromaffin cells. PACAP induced dose- and time-dependent increases in mRNAs for the catecholamine synthesizing enzymes, tyrosine hydroxylase (TH) and dopamine β-hydroxylase (DBH), with maximal 6- and 4-fold increases occurring at 8–16 h, respectively. The half-maximally and maximally effective PACAP concentrations for stimulation of TH and DBH gene expression were 0.5 and 3 nM, respectively. The TH protein level also showed an increase over the unstimulated basal level at 16–24 h in PACAP-stimulate cells. We previously demonstrated that PACAP activates both phospholipase C and adenylate cyclase in adrenal medullary cells. Addition of forskolin alone induced increases in mRNA expression of both TH and DBH. The phosphodiesterase inhibitor 3- isobutyl-1-methylxanthine potentiated the induction of TH and DBH mRNAs by PACAP. Addition of the protein kinase C activator phorbol 12-myristate 13-acetate (PMA) also caused increases in TH and DBH mRNA levels. In protein kinase C-downregulated cells pretreated with PMA for 24 h, the stimulatory effect of PACAP on TH and DBH gene expression was diminished. These results suggest that cAMP and protein kinase C mediate the PACAP-induced TH and DBH gene expression. Removal of extracellular Ca2+ with EGTA enhanced the PACAP-induced increases in both cellular cAMP and mRNA levels of TH and DBH, suggesting that Ca2+ has an inhibitory effect on the induction of TH and DBH mRNAs. In conclusion, the present study indicates that PACAP coordinately upregulates the gene expression of both TH and DBH by activating the cAMP and protein kinase C signaling pathways, leading to simulation of cate-cholamine sythesis, while C a2+ negatively regulates TH and DBH gene expression in porcine adrenal medullary cells.

Pertussis toxin pretreatment enhances catecholamine secretion induced by pituitary adenylate cyclase-activating polypeptide in cultured porcine adrenal medullary chromaffin cells: A possible role of the inositol lipid cascade

We determined how pertussis toxin (PTX) pretreatment alters PACAP-induced catecholamine secretion in cultured porcine adrenal medullary cells. Pretreatment of these cells with PTX (1 ng/ml for 24 h or 10 ng/ml for 6 h) markedly enhanced PACAP-induced catecholamine secretion. PTX pretreatment also produced a small increase in basal secretion and secretion in response to nicotine and carbachol, but the effect of the PACAP-induced secretion was most striking. We examined the role of the phosphoinositol cascade in potentiating the PACAP-induced catecholamine secretion by PTX and found that PACAP-induced accumulation of inositol phosphates in PTX-pretreated cells was significantly greater than that in untreated cells. Furthermore, removal of extracellular Ca 2+ and addition of Ca 2+ channel blockers inhibited the catecholamine secretion induced by PACAP in PTX-pretreated cells. From these results, we speculate that a PTX-sensitive G-protein tonically inhibits phospholipase C. PTX enhances the PACAP-induced secretion of catecholamine by blocking the action of this inhibitory G-protein.

Ca(2+)-dependent stimulatory effect of pituitary adenylate cyclase-activating polypeptide on catecholamine secretion from cultured porcine adrenal medullary chromaffin cells.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates catecholamine secretion from cultured porcine adrenal medullary chromaffin cells in a dose-dependent manner with the half-maximal and maximal doses of 30 nM and 1 microM, respectively. Either removal of extracellular Ca2+ or addition of Gd3+, an inorganic Ca2+ channel blocker, very potently inhibits PACAP-induced catecholamine secretion. Both nicardipine (1 microM) and methoxyverapamil (1 microM), blockers of voltage-dependent Ca2+ channels, are also effective in inhibiting PACAP-induced catecholamine secretion. When the intracellular free Ca2+ concentration ([Ca2+]i) is measured in a fura 2-loaded single chromaffin cell, PACAP is found to cause a sustained increase in [Ca2+]i by mobilizing Ca2+ from both extra- and intracellular pools. It is also found that PACAP stimulates the production of inositol phosphates in a dose-dependent manner, which is not abolished by removal of extracellular Ca2+ unlike the case of nicotine. PACAP increases cAMP content in chromaffin cells in a dose-dependent manner. Removal of extracellular Ca2+ enhances PACAP-induced cAMP production but strongly inhibits PACAP-induced catecholamine secretion. Pretreatment of cells with adenosine-3':5'-monophosphothioate, cyclic, Rp-isomer, a cAMP antagonist, does not block PACAP-induced catecholamine secretion. The addition of forskolin or 3-isobutyl-1-methylxanthine does not enhance the PACAP-induced catecholamine secretion. These results indicate that PACAP activates voltage-dependent Ca2+ channels and phospholipase C as well as adenylate cyclase in cultured porcine adrenal medullary cells and strongly suggest that PACAP-induced catecholamine secretion is mainly mediated by activation of voltage-dependent Ca2+ channels.

Ca(2+)-dependent stimulatory effect of pituitary adenylate cyclase- activating polypeptide on catecholamine secretion from cultured porcine adrenal medullary chromaffin cells

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates catecholamine secretion from cultured porcine adrenal medullary chromaffin cells in a dose-dependent manner with the half-maximal and maximal doses of 30 nM and 1 microM, respectively. Either removal of extracellular Ca2+ or addition of Gd3+, an inorganic Ca2+ channel blocker, very potently inhibits PACAP-induced catecholamine secretion. Both nicardipine (1 microM) and methoxyverapamil (1 microM), blockers of voltage-dependent Ca2+ channels, are also effective in inhibiting PACAP-induced catecholamine secretion. When the intracellular free Ca2+ concentration ([Ca2+]i) is measured in a fura 2-loaded single chromaffin cell, PACAP is found to cause a sustained increase in [Ca2+]i by mobilizing Ca2+ from both extra- and intracellular pools. It is also found that PACAP stimulates the production of inositol phosphates in a dose-dependent manner, which is not abolished by removal of extracellular Ca2+ unlike the case of nicotine. PACAP increases cAMP content in chromaffin cells in a dose-dependent manner. Removal of extracellular Ca2+ enhances PACAP-induced cAMP production but strongly inhibits PACAP-induced catecholamine secretion. Pretreatment of cells with adenosine-3':5'-monophosphothioate, cyclic, Rp-isomer, a cAMP antagonist, does not block PACAP-induced catecholamine secretion. The addition of forskolin or 3-isobutyl-1-methylxanthine does not enhance the PACAP-induced catecholamine secretion. These results indicate that PACAP activates voltage-dependent Ca2+ channels and phospholipase C as well as adenylate cyclase in cultured porcine adrenal medullary cells and strongly suggest that PACAP-induced catecholamine secretion is mainly mediated by activation of voltage-dependent Ca2+ channels.