Stimulation of formation of inositol phosphates in primary cultures of bovine adrenal chromaffin cells by angiotensin II, histamine, bradykinin, and carbachol

Prolactin-releasing peptide stimulates catecholamine release but not proliferation in rat pheochromocytoma PC12 cells

We examined the effect of prolactin-releasing peptide (PrRP) on catecholamine secretion and DNA synthesis in rat pheochromocytoma PC12 cells. We initially confirmed the expression of both PrRP and its receptor in PC12 cells. PrRP31 and PrRP20 (> or =10 nM) significantly increased dopamine secretion from PC12 cells. However, PrRP20-stimulated dopamine secretion was markedly weaker than that of PrRP31. Both EDTA (extracellular Ca2+ chelator) and BAPTA-AM (intracellular Ca2+ chelator) effectively suppressed PrRP31 (100 nM)-induced dopamine secretion. PrRP31and PrRP20 (> or =1 nM) significantly induced an increase in the level of cAMP. The PKA inhibitor H89 (at 10 microM) impeded PrRP31- and PrRP20-induced dopamine secretion. Finally, we confirmed that PrRP did not affect DNA synthesis. These results indicate that PrRP may regulate catecholamine secretion but not the mitogenic effects in chromaffin cells.

Angiotensin II causes calcium entry into bovine adrenal chromaffin cells via pathway(s) activated by depletion of intracellular calcium stores

The characteristics and properties of the increase in cytosolic [Ca2+] that occurs in bovine adrenal medullary chromaffin cells on exposure to angiotensin 11 have been investigated. In fura-2 loaded cells exposure to a maximally effective concentration of angiotensin II (100 nM) caused a rapid, but transient increase in cytosolic [Ca2+] followed by a lower plateau that was sustained as long as external Ca2+ was present. In the absence of external Ca2+ only the initial brief transient was observed. In cells previously treated with thapsigargin in Ca2+-free medium to deplete the internal Ca2+ stores, angiotensin II caused no increase in cytosolic [Ca2+] when external Ca2+ was absent. Reintroduction of external Ca2+ to thapsigargin-treated, store-depleted cells caused a sustained increase in cytosolic [Ca2+] that was not further increased upon exposure to angiotensin II. Analysis of the data suggests that in bovine chromaffin cells angiotensin II causes Ca2+ entry via a pathway(s) activated as a consequence of internal store mobilization, and entry through this pathway(s) forms the majority of the sustained Ca2+ influx evoked by angiotensin II.

Mechanisms in histamine-mediated secretion from adrenal chromaffin cells

The great majority of the sustained secretory response of adrenal chromaffin cells to histamine is due to extracellular Ca(2+) influx through voltage-operated Ca(2+) channels (VOCCs). This is likely to be true also for other G protein-coupled receptor (GPCR) agonists that evoke catecholamine secretion from these cells. However, the mechanism by which these GPCRs activate VOCCs is not yet clear. A substantial amount of data have established that histamine acts on H(1) receptors to activate phospholipase C via a Pertussis toxin-resistant G protein, causing the production of inositol 1,4,5-trisphosphate and the mobilisation of store Ca(2+); however, the molecular events that lead to the activation of the VOCCs remain undefined. This review will summarise the known actions of histamine on cellular signalling pathways in adrenal chromaffin cells and relate them to the activation of extracellular Ca(2+) influx through voltage-operated channels, which evokes catecholamine secretion. These actions provide insight into how other GPCRs might activate Ca(2+) influx in many excitable and non-excitable cells.

Inhibition and facilitation by pimobendan, a calcium sensitizer, of catecholamine secretion from bovine adrenal chromaffin cells

The effects of pimobendan, a Ca(2+) sensitizer with inhibitory action against cyclic-GMP-inhibited phosphodiesterase (PDE-III), on catecholamine (CA) secretion were studied in bovine adrenal chromaffin cells. In intact cells, pimobendan (10 - 100 microM) inhibited CA secretion stimulated by acetylcholine (10 and 30 microM) and 1,1-dimethyl-4-phenyl-piperazinium (DMPP) (3 and 10 microM), but facilitated CA secretion stimulated by high K(+) (30 mM), histamine (3 microM), and angiotensin-II (3 microM). Histamine and angiotensin-II had no effect on CA secretion in Ca(2+)-free medium. The inhibition or facilitation by pimobendan of the stimulation-evoked CA secretion was not affected by H-89 (1 microM) and H-8 (30 microM), inhibitors of cyclic-AMP-dependent protein kinase. Milrinone (10 and 30 microM) and amrinone (100 and 300 microM), inhibitors of PDE-III, did not affect the stimulation-evoked CA secretion. In beta-escin-permeabilized cells, pimobendan (10 - 100 microM) did not affect CA secretion stimulated by Ca(2+) (0.1 - 10 microM) in the presence and absence of MgATP (2 mM). These results indicate that pimobendan has dual effects, inhibition and facilitation, on CA secretion. The inhibition may be due to an inhibitory action on nicotinic receptors and the facilitation may be due to a facilitatory action on stimulation-induced Ca(2+) influx. Neither Ca(2+) sensitizing nor PDE-III inhibiting actions seem to be related to these effects.

Bradykinin-induced neuropeptide Y release by human pheochromocytoma tissue

Neuropeptide Y (NPY) and noradrenaline (NA) are frequently co-localized and co-released in the sympathetic nervous system. Since bradykinin (BK) is known to stimulate neurotransmitter release as NA in adrenal glands, we therefore hypothesized that BK might also be involved in the release of NPY. The effect of BK(1-9) on immunoreactive NPY (Ir-NPY) release was investigated in superfused human pheochromocytoma tissue. BK(1-9) (10(-7)-10(-5) M) was shown to induce a rapid Ir-NPY release in a concentration-dependent manner. This effect of BK(1-9) (10(-6) M) was mimicked by the B2 agonist [Phe(8)(CH(2)NH)Arg(9)]-bradykinin (10(-5) M) and blocked by the selective B2-receptor antagonist HOE140 (10(-5) M). Increasing Ir-NPY release was probably not mediated by nitric oxide (NO) since the outflow of Ir-NPY was not influenced by the NO synthase inhibitor N-omega-nitro-L-arginine methyl ester (L-NAME) (10(-4) M). In presence of bapta-AM (10(-5) M), a chelator of cytosolic calcium, W7 (10(-5) M), a calmodulin inhibitor, TMB-8 (10(-5) M), a blocker of intracellular calcium mobilization and ryanodine (10(-5) M), a selective inhibitor of the Ca(2+)-induced release mechanism, the NPY release by BK(1-9) was significantly inhibited by 126%, 98%, 91%, and 94%, respectively. These results indicate that BK increased the release of NPY by the tumor acting through the interaction with the BK-B2 receptor and request intracellular calcium mobilization independently of a NO mechanism.

Phospholipase C-mediated signalling is not required for histamine-induced catecholamine secretion from bovine chromaffin cells

A possible role for signalling through phospholipase C in histamine-induced catecholamine secretion from bovine adrenal chromaffin cells has been investigated. Secretion evoked by histamine over 10 min was not prevented by inhibiting inositol-1,4,5-trisphosphate receptors with 2-APB, by blocking ryanodine receptors with a combination of ryanodine and caffeine, or by depleting intracellular Ca(2+) stores by pretreatment with thapsigargin. Inhibition of protein kinase C with Ro31-8220 also failed to reduce secretion. Inhibition of phospholipase C with ET-18-OCH(3) reduced both histamine- and K(+) -induced inositol phosphate responses by 70-80% without reducing their secretory responses. Stimulating phospholipase C with Pasteurella multocida toxin did not evoke secretion or enhance the secretory response to histamine. The secretory response to histamine was little affected by tetrodotoxin or by substituting extracellular Na(+) with N -methyl-d-glucamine(+) or choline(+), or by substituting external Cl(-) with nitrate(-). Blocking various K(+) channels with apamin, charybdotoxin, Ba(2+), tetraethylammonium, 4-aminopyridine, tertiapin or glibenclamide failed to reduce the ability of histamine to evoke secretion. These results indicate that histamine evokes secretion by a mechanism that does not require inositol-1,4,5-trisphosphate-mediated mobilization of stored Ca(2+), diacylglycerol-mediated activation of protein kinase C, or activation of phospholipase C. The results are consistent with histamine acting by depolarizing chromaffin cells through a phospholipase C-independent mechanism.

Histamine promotes excitability in bovine adrenal chromaffin cells by inhibiting an M-current

The current study has investigated the electrophysiological responses evoked by histamine in bovine adrenal chromaffin cells using perforated-patch techniques. Histamine caused a transient hyperpolarization followed by a sustained depolarization of 7.2 +/- 1.4 mV associated with an increase in spontaneous action potential frequency. The hyperpolarization was abolished after depleting intracellular Ca(2+) stores with thapsigargin (100 nM), and was reduced by 40 % with apamin (100 nM). Membrane resistance increased by about 60 % during the histamine-induced depolarization suggesting inhibition of a K(+) channel. An inward current relaxation, typical of an M-current, was observed in response to negative voltage steps from a holding potential of -30 mV. This current reversed at -81.6 +/- 1.8 mV and was abolished by the M-channel inhibitor linopirdine (100 microM). During application of histamine, the amplitude of M-currents recorded at a time corresponding with the sustained depolarization was reduced by 40 %. No inward current rectification was observed in the range -150 to -70 mV, and glibenclamide (10 microM) had no effect on either resting membrane potential or the response to histamine. The results show that an M-current is present in bovine chromaffin cells and that this current is inhibited during sustained application of histamine, resulting in membrane depolarization and increased discharge of action potentials. These results demonstrate for the first time a possible mechanism coupling histamine receptors to activation of voltage-operated Ca(2+) channels in these cells.

In vivo evidence for a role of protein kinase C in peripheral nociceptive processing

1. The present study was designed to characterize the nociceptive response induced by protein kinase C (PKC) peripheral activation and to investigate if this biochemical event is important for the nociceptive response induced by formaldehyde, and bradykinin (BK). 2. Intraplantar injection of phorbol-12,13-didecanoate (PDD; 0.01, 0.1 or 1 microg), a PKC activator, but not of 4 alpha-PDD (inactive analogue), dose-dependently induced thermal hyperalgesia in rats. This response was not observed at the contralateral hindpaw. Intraplantar injection of PDD (0.01, 0.1 or 1 microg) also induced mechanical allodynia. In mice, injection of PDD (0.1 or 1 microg) into the dorsum of the hindpaw induced a spontaneous licking behaviour. 3. Intraplantar co-injection of chelerythrine (10 or 50 microg), a PKC inhibitor, attenuated the thermal hyperalgesia induced by PDD (0.1 microg) in rats. 4. The second phase of the nociceptive response induced by the injection of formaldehyde (0.92%, 20 microl) into the dorsum of mice hindpaws was inhibited by ipsi-, but not contralateral, pre-treatment with chelerythrine (1 microg). 5. Intraplantar injection of BK (10 microg) induced mechanical allodynia in rats. Ipsi- but not contralateral injection of bisindolylmaleimide I (10 microg), a PKC inhibitor, inhibited BK-induced mechanical allodynia. 6. In conclusion, this study demonstrates that PKC activation at peripheral tissues leads to the development of spontaneous nociceptive response, thermal hyperalgesia and mechanical allodynia. Most importantly, it also gives in vivo evidence that peripheral PKC activation is essential for the full establishment of the nociceptive response induced by two different inflammatory stimuli.

Bidirectional modulation of exocytosis by angiotensin II involves multiple G-protein-regulated transduction pathways in chromaffin cells

Angiotensin II (AngII) receptors couple to a multitude of different types of G-proteins resulting in activation of numerous signaling pathways. In this study we examined the consequences of this promiscuous G-protein coupling on secretion. Chromaffin cells were voltage-clamped at -80 mV in perforated-patch configuration, and Ca(2+)-dependent exocytosis was evoked with brief voltage steps to +20 mV. Vesicle fusion was monitored by changes in membrane capacitance (DeltaC(m)), and released catecholamine was detected with single-cell amperometry. Ca(2+) signaling was studied by recording voltage-dependent Ca(2+) currents (I(Ca)) and by measuring intracellular Ca(2+) ([Ca(2+)](i)) with fura-2 AM. AngII inhibited I(Ca) (IC(50) = 0.3 nm) in a voltage-dependent, pertussis toxin (PTX)-sensitive manner consistent with G(i/o)-protein coupling to Ca(2+) channels. DeltaC(m) was modulated bi-directionally; subnanomolar AngII inhibited depolarization-evoked exocytosis, whereas higher concentrations, in spite of I(Ca) inhibition, potentiated DeltaC(m) fivefold (EC(50) = 3.4 nm). Potentiation of exocytosis by AngII involved activation of phospholipase C (PLC) and Ca(2+) mobilization from internal stores. PTX treatment did not affect AngII-dependent Ca(2+) mobilization or facilitation of exocytosis. However, protein kinase C (PKC) inhibitors decreased the facilitatory effects but not the inhibitory effects of AngII on stimulus-secretion coupling. The AngII type 1 receptor (AT1R) antagonist losartan blocked both inhibition and facilitation of secretion by AngII. The results of this study show that activation of multiple types of G-proteins and transduction pathways by a single neuromodulator acting through one receptor type can produce concentration-dependent, bi-directional regulation of exocytosis.

Differential secretion of adrenaline and noradrenaline in response to various secretagogues from bovine chromaffin cells

1. Differential secretion of adrenaline (Adr) and noradrenaline (NA) in response to various secretagogues was studied in bovine adrenal chromaffin cells. 2. Acetylcholine (ACh; 3-300 mumol/L), 1,1-dimethyl-4-phenyl-piperazinum (DMPP; 1-100 mumol/L), high K+ (20-60 mmol/L), calcimycin (1-100 mumol/L), histamine (0.3-30 mumol/L) and angiotensin (Ang)II (0.3-30 mumol/L) induced the secretion of a 1.3-2-fold greater percentage of NA stores than Adr stores in intact cells. 3. In beta-escin-permeabilized cells, Ca2+ (0.1-30 mumol/L) induced a greater secretion of Adr and NA in the presence of MgATP (2 mmol/L) than in the absence of MgATP. The percentage of NA secreted was 1.4- and 1.5-fold greater than that of Adr in the presence and absence of MgATP, respectively. 4. The ATP-independent phase of the Ca(2+)-dependent exocytosis is thought to be associated with the final step that ultimately leads to fusion, while the ATP-dependent phase is thought to be associated with the vesicle priming reaction. Therefore, the preferential secretion of NA in response to ACh, DMPP, high K+, calcimycin, histamine and AngII may be due, at least in part, to the greater effectiveness of Ca2+ in producing exocytosis in NA-containing cells.

Ca(2+) influx stimulated phospholipase C activity in bovine adrenal chromaffin cells: responses to K(+) depolarization and histamine

The role of Ca(2+) influx in activating phospholipase C in bovine adrenal chromaffin cells has been investigated. Phospholipase C activity in response to K(+) depolarization (56 mM) was blocked by the L-type Ca(2+) channel antagonist nifedipine and partially inhibited by the omega-conotoxins GVIA and MVIIC. In contrast, phospholipase C activity in response to histamine receptor activation was unaffected by omega-conotoxin GVIA and partially inhibited by omega-conotoxin MVIIC or nifedipine. This response was however markedly inhibited by the non-selective Ca(2+) channel antagonists La(3+) or 1-[beta-[3-(4-Methoxyphenyl)propoxy]-4-methoyphenethyl]-H-imidazol e (SKF-96365). Despite this Ca(2+) dependence phospholipase C activity was not increased during periods of "capacitative" Ca(2+) inflow generated by histamine-, caffeine- or thapsigargin-mediated depletion of internal Ca(2+) stores. Thus, while Ca(2+) influx in response to K(+) depolarization or G-protein receptor activation can increase phospholipase C activity in these cells, in the latter case it appears to be ineffective unless there is concurrent agonist occupation of the receptor.

Effect of Gd3+ on bradykinin-induced catecholamine secretion from bovine adrenal chromaffin cells

1. The effects of Gd3+ on bradykinin- (BK-) induced catecholamine secretion, 45Ca2+ efflux and cytosolic [Ca2+] were studied using bovine adrenal chromaffin cells. 2. BK increased secretion in a Ca2+-dependent manner. From 1 - 100 microM, Gd3+ progressively inhibited secretion induced by 30 nM BK to near-basal levels, however from 0.3 - 3 mM Gd3+ dramatically enhanced BK-induced secretion to above control levels. Gd3+ also increased basal catecholamine secretion by 2 - 3 fold at 1 mM. These effects were mimicked by Eu3+ and La3+. 3. Gd3+ enhanced secretion induced by other agonists that mobilize intracellular Ca2+ stores, but simply blocked the response to K+. 4. Gd3+ still enhanced basal and BK-induced secretion in Ca2+-free solution or in the presence of 30 microM SKF96365, however both effects of Gd3+ were abolished after depleting intracellular Ca2+ stores. 5. Gd3+ (1 mM) reduced the rate of basal 45Ca2+ efflux by 57%. In Ca2+-free buffer, BK transiently increased cytosolic [Ca2+] measured with Fura-2. The [Ca2+] response to BK was substantially prolonged in the presence of Gd3+ (1 mM). 6. The results suggest that Gd3+ greatly enhances the efficacy of Ca2+ released from intracellular stores in evoking catecholamine secretion, by inhibiting Ca2+ extrusion from the cytosol. This suggests that intracellular Ca2+ stores are fully competent to support secretion in chromaffin cells to levels comparable to those evoked by extracellular Ca2+ entry. Drugs that modify Ca2+ extrusion from the cell, such as lanthanide ions, will be useful in investigating the mechanisms by which intracellular Ca2+-store mobilization couples to Ca2+-dependent exocytosis.

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 Ca(2+) 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.

Cd2+ and Co2+ at micromolar concentrations mobilize intracellular Ca2+ via the generation of inositol 1,4,5-triphosphate in bovine chromaffin cells

To understand the mechanisms underlying the Cd2+- and Co2+-induced intracellular Ca2+ mobilization, we measured the levels of inositol phosphates using bovine chromaffin cells. Studies using HPLC indicated that Cd2+, Co2+ and methacholine significantly increased the generation of 1,4,5-IP3. The results suggest that Cd2+ and Co2+ mobilize Ca2+ from IP3-sensitive Ca2+ stores, possibly through the presumptive Cd2+ receptor.

Activation of tyrosine hydroxylase by histamine in bovine chromaffin cells

Acute activation of tyrosine hydroxylase by histamine has been studied in cultured bovine chromaffin cells. Tyrosine hydroxylase activity was determined in situ by measuring 14CO2 release following the hydroxylation and rapid decarboxylation of 14C-tyrosine offered to the cells. Histamine increased tyrosine hydroxylase activity 2-fold over 10 min with an EC50 of 0.3 microM and maximal response at 10 microM. Tyrosine hydroxylase activation was detectable within 1-2 min and maintained for at least 10 min. The effect of histamine was fully blocked by the H1 antagonist mepyramine, but unaffected by H2 (cimetidine) and H3 (thioperamide) antagonists. It was mimicked by Nalpha-methylhistamine and the H1 agonist 2-thiazolylethylamine, but not by H2 (dimaprit) or H3 (R)alpha-methylhistamine) agonists. The response to histamine was reduced by 70% by removing extracellular Ca2+ and abolished by removing extracellular Ca2+ and chelating intracellular Ca2+ with BAPTA. Tyrosine hydroxylase activation by histamine was unaffected by the protein kinase C inhibitor Ro 31-8220 but was completely blocked by the protein kinase A inhibitor H89. The results indicate that histamine activates tyrosine hydroxylase and that this effect is mediated through H1 receptors by a mechanism that depends on both extracellular and intracellular Ca2+ and that requires protein kinase A.

Exocytosis in chromaffin cells of the adrenal medulla

The chromaffin cell has been used as a model to characterize releasable components present in secretory granules and to understand the cellular mechanisms involved in catecholamine release. Recent physiological and biochemical developments have revealed that molecular mechanisms implicated in granule trafficking are conserved in all eukaryotic species: a rise in intracellular calcium triggers regulated exocytosis, and highly conserved proteins are essential elements which interact with each other to form a molecular scaffolding, ensuring the docking of granules at the plasma membrane, and perhaps membrane fusion. However, the mechanisms regulating secretion are multiple and cell specific. They operate at different steps along the life of a granule, from the time of granule biosynthesis up to the last step of exocytosis. With regard to cell specificity, noradrenaline and adrenaline chromaffin cells display different receptor and signaling characteristics that may be important to exocytosis. Characterization of regulated exocytosis in chromaffin cells provides not only fundamental knowledge of neurosecretion but is of additional importance as these cells are used for therapeutic purposes.

Interaction between G protein-operated receptors eliciting secretion in rat adrenals. A possible role of protein kinase C

Catecholamine release induced by angiotensin II, histamine, bradykinin and methacholine from the rat adrenal gland perfused in vitro was studied under conditions in which the activity of protein kinase C (PKC) was modified. Perfusion of glands with 10 nM bradykinin abolished, in a reversible way, the secretion induced by short pulses of angiotensin II, histamine and methacholine but did not modify the release evoked by 23.6 mM KCl (high K+). Perfusion with histamine or methacholine (30 microM) inhibited the secretion induced by the other agents by 30-50%, whereas incubation with angiotensin II (100 nM) caused little or no reduction in the release evoked by the other agents. The treatment of glands with 1 nM of the PKC activator phorbol 12,13-dibutyrate (PDBu) suppressed the responses induced by angiotensin II, histamine and methacholine, did not affect those evoked by bradykinin, and potentiated the secretion evoked by high K+. The adenylate cyclase stimulator forskolin (1 microM) did not affect the basal secretion but strongly potentiated the release evoked by all secretagogues used, suggesting a role for protein kinase A (PKA) downstream of the receptor. The PKC inhibitor Ro-31-8220 partially reversed the inhibitory effect of bradykinin. Our results suggest that angiotensin II, histamine and muscarinic receptors share some common transduction mechanism that is regulated by PKC. PKC activity was enhanced by these agents PDBu >> bradykinin = histamine > methacholine = angiotensin II. Bradykinin receptor transduction does not appear to be regulated by PKC.

Potentiation of histamine-induced catecholamine secretion by ouabain in cultured bovine adrenal chromaffin cells is dependent on calcium and sodium influx

The effects of histamine on catecholamine secretion from cultured bovine adrenal chromaffin cells were studied in the presence of ouabain, an inhibitor of Na+-K+ ATPase. The purpose of this study was to determine whether Na+, as well as Ca2+, was involved in histamine receptor-mediated catecholamine secretion. Histamine (10(-8)-10(-5) M)-induced catecholamine secretion was markedly potentiated by addition of ouabain (10(-5) M) and was inhibited by a histamine-H1 receptor antagonist or incubation in a Ca2+-free medium. Histamine-induced 45Ca2+ influx was also potentiated by addition of ouabain. Ouabain alone or in the presence of histamine increased 22Na+ influx into the cells. In an additional set of experiments, cells were preincubated in the presence or absence of Na+ for 30 min (+/- histamine and ouabain), washed and then catecholamine secretion was measured following exposure to 2.2 mM Ca2+ for 15 min. Preincubation with histamine alone with or without Na+ had no effect of Ca2+-induced secretion of catecholamine. Preincubation with ouabain alone or with ouabain plus histamine produced a slight stimulation of catecholamine secretion in Na+-free medium and a large stimulation in Na+-containing medium. These results suggested that stimulation of the histamine-H1 receptor and inhibition of the Na+ pump both increase intracellular Na+ levels, resulting in increases in Ca2+ influx and catecholamine secretion.

Comparison of cytosolic Ca2+ and exocytosis responses from single rat and bovine chromaffin cells

The relationship between cytosolic Ca2+ and catecholamine secretion during stimulus-secretion coupling has been examined at individual chromaffin cells isolated from the cow and rat. Vesicular catecholamine exocytosis was determined via amperometric measurements with carbon fibre microelectrodes and fura-2 was used for simultaneous fluorescent monitoring of cytosolic Ca2+ at the same cell. Individual secretory vesicles in cells from the two species were found to release similar amounts of catecholamine. In addition, the time courses for secretion from individual vesicles was similar with rat and bovine chromaffin cells. The total quantity of catecholamine released and the change in cytosolic Ca2+ were also similar in response to exposure to K+ (60 mM), 1,1-dimethyl-4-phenylpiperazinium (50 microM), and histamine (50 microM), although both responses were more prolonged following 1,1-dimethyl-4-phenylpiperazinium and histamine at bovine cells. Agents that mobilize intracellular Ca(2+)-stores such as methacholine, caffeine and bradykinin resulted in different cytosolic Ca2+ and exocytosis responses at the rat and bovine chromaffin cells. Results indicate a heightened Ca(2+)-store activity or a more filled state in chromaffin cells from the rat. The results of this study clearly show that single-cell techniques can be used to characterize stimulus-secretion coupling. The requirement for lower numbers of cells with these techniques means that chromaffin cells from rodents can be routinely employed. This can be advantageous to minimize biological variability which occurs with organs obtained from slaughter houses and enables the investigation of genetically-altered animals.

The effect of the angiotensin II (AT1A) receptor stably transfected into human neuroblastoma SH-SY5Y cells on noradrenaline release and changes in intracellular calcium

A stable cell line expressing the angiotensin II (AII) receptor has been obtained by transfecting the human neuroblastoma SH-SY5Y with the plasmid pCEP4 containing the entire coding region of the rat angiotensin AII receptor AT1A. Angiotensin II (AII; 1-100 nM) evokes the release of [3H]noradrenaline ([3H]NA) in this cell line. Pretreatment with 100 nM 12-O-tetradecanoylphorbol-13-acetate (TPA) enhances the AII-evoked release of [3H]NA approximately two-fold. Removal of extracellular Ca2+ ([Ca2+]o) decreases 100 nM AII-evoked release of [3H]NA by over 50% both in the presence and absence of TPA. AII increases intracellular Ca2+ ([Ca2+]i) in this cell line which is consistent with the AT1A receptor being coupled to phospholipase C. Pretreatment with 100 nM TPA for 8 min attenuated the effect of AII on [Ca2+]i. The effects of AT1A receptor stimulation are therefore regulated differently in this cell line by activation of protein kinase C (PKC). Thus a useful cell line has been obtained from the human neuroblastoma SH-SY5Y in which to study at the molecular level the mechanism(s) by which AII regulates NA release.

Regulatory mechanism of calcium efflux from cultured bovine adrenal chromaffin cells induced by extracellular ATP

The effect of adenosine-5'-triphosphate (ATP) on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. ATP stimulated the efflux of 45Ca2+ from the cells in a concentration-dependent manner (0.01-1 mM). The 45Ca2+ efflux from the cells was also stimulated by adenosine-5'-O-(3-thiotriphosphate) (ATP-gamma s), alpha beta-methylene-ATP and adenosine-5'-diphosphate (ADP), but was not by adenosine-5'-monophosphate (AMP) and adenosine. The ATP-stimulated 45Ca2+ efflux was not affected by deprivation of the extracellular Ca2+ and Mg2+, but was dependent on the extracellular Na+ concentrations. ATP increased the influx of 22Na+ into the cells. These results indicate that ATP stimulates extracellular Na(+)-dependent 45Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably through its stimulatory effect on membrane Na+/Ca2+ exchange.

Potentiation by ouabain of bradykinin-induced catecholamine secretion and calcium influx into cultured bovine adrenal chromaffin cells: evidence for involvement of Na+ influx associated with the bradykinin B2-receptor

The effect of bradykinin (BK), in the presence of ouabain, an inhibitor of Na(+)-K+ ATPase, on catecholamine (CA) secretion was studied in cultured bovine adrenal chromaffin cells, to determine whether Na+, as well as Ca2+, is involved in BK-receptor mediated CA secretion. BK (10(-8)-10(-5) M)-induced CA secretion was markedly potentiated by addition of ouabain (10(-5) M), was blocked by a BK-B2 receptor antagonist, and was decreased in Ca(2+)-free medium. BK-induced increase in 45Ca2+ influx was also potentiated by addition of ouabain. The cultured cells were first incubated with BK for 30 min in Ca(2+)-free medium in the presence or absence of ouabain and then stimulated for 15 min with Ca(2+)-medium without BK or ouabain. Prior stimulation of the cells, BK induced 22Na+ influx and increased Ca(2+)-induced CA secretion and these stimulatory effects of BK were potentiated by added ouabain. When the cells were stimulated with BK and ouabain in Na(+)-free sucrose medium, the Ca(2+)-induced CA secretion was greatly reduced. These results indicated that activation of the BK-B2 receptor and inhibition of the Na+ pump both increase the intracellular Na+ level, resulting in increase in Ca2+ influx and CA secretion.

Veratridine-induced oscillations of cytosolic calcium and membrane potential in bovine chromaffin cells

1. Veratridine (VTD) induced large oscillations of the cytosolic Ca2+ concentration ([Ca2+]i) and the membrane potential (Vm) in otherwise silent bovine chromaffin cells loaded with fura-2. 2. Depletion of the intracellular Ca2+ stores by thapsigargin or ryanodine did not affect these oscillations. Caffeine had a complex effect, decreasing them in cells with high activity but increasing them in cells with low activity. 3. The [Ca2+]i oscillations required extracellular Ca2+ and Na+ and were blocked by Ni2+ or tetrodotoxin. They were antagonized by high external concentrations of Mg2+ and/or Ca2+. 4. The oscillations of Vm had three phases: (i) slow depolarization (20 mV in 10-40 s); (ii) further fast depolarization (30 mV in 1 s); and (iii) rapid (5 s) repolarization. [Ca2+]i decreased during (i), increased quickly during (ii) with a 1 s delay with regard to the peak depolarization, and decreased during (iii). 5. Slight depolarizations increased the frequency of the oscillations whereas large depolarizations decreased it. 6. The Ca(2+)-dependent K+ channel blocker apamin increased the duration and decreased the frequency of the oscillations. 7. We propose the following mechanism for the oscillations: (i) the membrane depolarizes slowly by a decrease of potassium conductance (gK), perhaps due to a gradual decrease of [Ca2+]i; (ii) the threshold for activation of Na+ channels (decreased by VTD) is reached, producing further depolarization and recruiting Ca2+ channels, and inactivation of both Ca2+ and VTD-poisoned Na+ channels is slow; and (iii) gK increases, aided by activation of Ca(2+)-dependent K+ channels by the increased [Ca2+]i, and the membrane repolarizes. The contribution of the Na+ channels seems essential for the generation of the oscillations. 8. Bovine chromaffin cells have the machinery required for [Ca2+]i oscillations even though the more physiological stimulus tested here (high K+, field electrical stimulation, nicotinic or muscarinic agonists) produced mainly non-oscillatory responses.

Angiotensin II receptor subtypes and phosphoinositide hydrolysis in rat adrenal medulla

Angiotensin II (ANG) receptor subtypes were characterized by quantitative autoradiography after incubation with the ANG agonist [124I]Sar1-ANG in rat adrenal medulla. ANG receptors are highly localized in adrenal medulla. Specific binding was displaced by 4% and by 95% with the AT, receptor blocker losartan and the AT2 receptor competitor CGP 42112A, respectively. Analysis of competition curves indicated relative binding potencies for the AT2 population of CGP 42112A>PD 123319> PD 123177. ANG stimulated +-nositol phosphate formation in a dose-dependent manner in rat adrenal medulla. Losartan at concentrations of 10(-9) to 10(-5) M antagonized the effect of ANG, whereas PD 123177 or PD 123319 had no antagonistic action. However, at a higher concentration (10(-5) M) PD 123177 or PD 123319 potentiated the effect of ANG on InsP1-accumulation. In the presence of PD 123319 (10(-5) M) ANG dose-response curve was shifted to the left with no change in the maximal effect. This affect was blocked by the addition of losartan (10(-5) M). On the contrary, the addition of CGP 42112A (10(-6) M) inhibited ANG-induced increase in InsP1-accumulation. On the other hand, ANG and CGP 42112A reduced basal cyclic GMP formation, this effect was partially reverted by sodium orthovanadate, a phosphotyrosine phosphatase inhibitor. Our results further demonstrate the presence of two ANG receptor subtypes in adrenal medulla: ANG binding to AT, receptor stimulates inositol phospholipid metabolism, whereas ANG binding to AT2 receptors decreases both inositol phosphate production and cGMP formation.

Stimulatory effect of angiotensin II on calcium efflux from cultured bovine adrenal chromaffin cells

The effect of angiotensin II on Ca2+ mobilization in cultured bovine adrenal chromaffin cells was examined. Angiotensin II (10(-7)M) increased the intracellular free Ca2+ level ([Ca2+]i) to a peak in the presence or absence of extracellular Ca2+, followed by decrease with time. Angiotensin II (10(-9)-10(-6)M) also stimulated 45Ca2+ efflux from cultured bovine adrenal chromaffin cells in a concentration-dependent manner. Its stimulatory effect on 45Ca2+ efflux was inhibited by the angiotensin II antagonist [Sar1, Ile8]-angiotensin II or [Sar1, Val5, Ala8]-angiotensin II. The increase in angiotensin II-stimulated 45Ca2+ efflux was dependent on the extracellular Na+ concentration. Angiotensin II also increased 22Na+ influx into the cells. These results indicate that stimulation of the angiotensin II receptor induces extracellular Na(+)-dependent Ca2+ efflux from cultured bovine adrenal chromaffin cells, probably by acceleration of Na+/Ca2+ exchange.

Histamine-induced Ca2+ entry precedes Ca2+ mobilization in bovine adrenal chromaffin cells

The relationship between histamine-induced Ca2+ mobilization and Ca2+ entry in bovine adrenal chromaffin cells has been investigated. Stopped-flow fluorimetry of fura-2-loaded chromaffin cell populations revealed that 10 microM histamine promoted entry of Ca2+ or Mn2+ without measurable delay (< or = 20 ms), through a pathway that was insensitive to the dihydropyridine antagonist nifedipine. In the absence of extracellular Ca2+, or in the presence of 100 microM La3+, a blocker of receptor-mediated Ca2+ entry, 10 microM histamine triggered an elevation in intracellular calcium concentration ([Ca2+]i), but only after a delay of approx. 200 ms, which presumably represented the time required to mobilize intracellular Ca2+. These data suggested that histamine-induced bivalent-cation entry precedes extensive Ca2+ mobilization in chromaffin cells. In order to confirm that histamine can promote Ca2+ entry largely independently of mobilizing intracellular Ca2+, the ability of histamine to promote Ca2+ entry into cells whose intracellular Ca2+ store had been largely depleted was assessed. Fura-2-loaded chromaffin cells were treated with 10 microM ryanodine together with 40 mM caffeine, to deplete the hormone-sensitive Ca2+ store. This resulted in an approx. 95% inhibition of histamine-induced Ca2+ release. Under these conditions, histamine was still able to promote an entry of Ca2+ that was essentially indistinguishable from that promoted in control cells. In single cells, introduction of heparin (100 mg/ml), but not de-N-sulphated heparin (100 mg/ml), abolished the histamine-induced rise in [Ca2+]i. All these data suggest that histamine can induce G-protein- or inositol phosphate-dependent rapid (< or = 20 ms) Ca2+ entry without an extensive intracellular mobilization response in chromaffin cells, which points to activation of an entry mechanism distinct from the Ca(2+)-release-activated Ca2+ channel found in non-excitable cells.

Stimulatory effect of pituitary adenylate cyclase-activating polypeptide on catecholamine synthesis in cultured bovine adrenal chromaffin cells: involvements of tyrosine hydroxylase phosphorylation caused by Ca2+ influx and cAMP

In cultured bovine adrenal chromaffin cells, pituitary adenylate cylase-activating polypeptide (PACAP) stimulated [14C]catecholamine synthesis from [14C]tyrosine (but not from [14C]DOPA) in a concentration-dependent manner, causing maximal stimulation at 10(-7) M. The stimulatory action of PACAP was not affected by staurosporine (an inhibitor of protein kinase C) or in the cells in which protein kinase C was down-regulated by prolonged exposure to TPA (an activator of protein kinase C), whereas it was partially attenuated in Ca(2+)-free medium. PACAP (10(-7) M) increased the formation of [3H]inositol phosphates, [Ca2+]i and 45Ca2+ uptake as well as cAMP. The peptide also stimulated the phosphorylation of tyrosine hydroxylase, the enzyme catalyzing the rate-limiting step in catecholamine synthesis. Catecholamine synthesis and tyrosine hydroxylase phosphorylation stimulated by the maximal effective concentration of dibutyryl cAMP or high K+, which activates Ca2+ uptake, were further enhanced by PACAP, suggesting that both cAMP- and Ca(2+)-dependent protein kinases may be involved in the stimulation of tyrosine hydroxylase phosphorylation and catecholamine synthesis caused by PACAP.

Mechanism of histamine-induced calcium efflux from cultured bovine adrenal chromaffin cells: possible involvement of an Na+/Ca2+ exchange mechanism

The effect of stimulation of the histamine receptor on Ca2+ mobilization in cultured bovine adrenal chromaffin cells was examined. Histamine (10(-5) M) increased the intracellular free Ca2+ ([Ca2+]i) to a peak in the presence or absence of extracellular Ca2+, followed by decrease with time. Histamine (10(-8)-10(-5) M) also stimulated 45Ca2+ efflux from cultured bovine adrenal chromaffin cells in a concentration dependent manner. Its stimulatory effect on 45Ca2+ efflux was inhibited by the specific histamine H1 receptor antagonist mepyramine. The increase in histamine-stimulated 45Ca2+ efflux was inhibited by deprivation of extracellular Na+ and by the Na+/Ca2+ exchange inhibitor amiloride. In addition, histamine stimulated 22Na+ influx into the cells, and this action was inhibited by amiloride. These results suggest that stimulation of the histamine H1 receptor regulates Na+/Ca2+ exchange in cultured bovine adrenal chromaffin cells.

ABT-200, a norepinephrine uptake inhibitor, blocks Ca2+ signals in chromaffin cells

We previously described inhibition by racemic (+/-)-(1'R*,3R*)-3-phenyl-1- [1',2',3',4'-tetrahydro-5',6'-methylenedioxy-1'- napthalenyl-methyl]-pyrrolidine methanesulfonate (ABT-200), and its two constituent enantiomers, SS,ABT-200 and RR,ABT-200, of nicotine-stimulated but not histamine-stimulated catecholamine release from bovine adrenal chromaffin cells. To test the hypothesis that this inhibition reflects a blockade of Ca2+ influx, we used fura-2 loaded chromaffin cells to investigate cytosolic Ca2+ signals. We found that SS,ABT-200 inhibited nicotine- and K(+)-stimulated Ca2+ signals, both of which depend on Ca2+ influx. However, the early phase of the histamine-stimulated Ca2+ signals, which depends on Ca2+ mobilization from intracellular stores, was unaffected. We also examined ion flux through the nicotinic receptor by measuring 86rubidium+ (86Rb+) efflux from preloaded mouse midbrain synaptosomes. We found that SS,ABT-200 partially inhibited nicotine-stimulated 86Rb+ efflux, suggesting that it blocks ion flux through the nicotinic receptor directly. These data support a model in which ABT-200 blocks nicotine-stimulated catecholamine release by inhibiting cation flux through multiple channels.

Receptor-mediated internalization of angiotensin II in bovine adrenal medullary chromaffin cells in primary culture

Binding and internalization of angiotensin II (AII) were studied on bovine adrenal medullary cells in primary culture. Binding of [125I]AII was reversible, saturable, specific and showed high affinity. AII was found to be internalized by bovine adrenal medullary cells. Monensin increased whereas phenylarsine oxide (PhAsO) decreased the internalization. Excess of unlabelled AII or saralasin could block the internalization, indicating a receptor mediated internalization process. The kinetic analysis indicated that, during the first 4 min, about 25% of the membrane bound ligand was internalized per min and the recycling of internalized ligand and receptor initiated around 4 min.

Calcium signalling in bovine adrenal chromaffin cells: additive effects of histamine and nicotine

In a previous report, we described the ability of two secretogogues, histamine and nicotine, to stimulate additive effects on catecholamine (CA) release and synapsin II phosphorylation in bovine adrenal chromaffin cells (BACC) [Firestone and Browning (1992), J. Neurochem., 58:441-447]. We hypothesized that these results were due to the combined effects on cytosolic Ca++ of the two distinct signalling pathways. We therefore examined the intracellular Ca++ signals stimulated by histamine and nicotine, alone and together. In Ca(++)-deficient medium, nicotine-stimulated signals were abolished, whereas histamine-stimulated signals were maintained, demonstrating that nicotine depended entirely on Ca++ influx for its effects. Indeed, the nicotine-stimulated signal could also be prevented using a Ca++ channel blocker, nicardipine. Further, the observation that exposure of BACC to thapsigargin reduced histamine-stimulated Ca++ signals verified that histamine mobilizes Ca++ from intracellular stores. Thus, the two secretogogues mobilize Ca++ from distinct pools. When BACC were stimulated with the two secretogogues together, the resulting Ca++ signal was greater than that from either alone. These data are consistent with a model in which two distinct sources of Ca++ can summate within the cell, producing a greater Ca++ signal and, hence, a greater effect on neurotransmitter release.

Bradykinin-evoked release of [3H]noradrenaline from the human neuroblastoma SH-SY5Y

Bradykinin (BK) evoked [3H]noradrenaline ([3H]NA) release from the human neuroblastoma SH-SY5Y and this was enhanced by pre-treatment with 12-O-tetradecanoylphorbol 13-acetate (TPA) for 8 min. This effect of BK was inhibited by 500 microM [D-Phe7]BK and 100 microM [Thi5,8,D-Phe7]BK but not by 500 microM [Des-Arg9,Leu8]BK. The BK (B1)-agonist [Des-Arg9]BK did not evoke [3H]NA release. This suggested that SH-SY5Y expressed BK (B2)-receptors coupled to the release of [3H]NA. BK acting at B2-receptors, also elevated intracellular calcium and depolarized SH-SY5Y cells. Although pre-treatment of SH-SY5Y cells with TPA enhanced BK-evoked [3H]NA release, the elevation of intracellular calcium [Ca2+]; was decreased by about 50%. BK-evoked release of [3H]NA in cells not pre-treated with phorbol ester was only 23% dependent on extracellular calcium. In comparison, following phorbol ester treatment approximately 40% of [3H]NA release was dependent on extracellular calcium. Nifedipine (5 microM), CoCl2 (1 mM) and NiCl2 (1 mM) inhibited NA release in SH-SY5Y cells pre-treated with TPA by 16.0, 47 and 44%, respectively. The results of this study showed that BK, acting at B2-receptors, activated [3H]NA release in SH-SY5Y. Part of this effect appeared to be due to activation of L-type calcium channels but the majority of BK-evoked [3H]NA release in SH-SY5Y cells appeared to depend on [Ca2+]i.

Differential stimulation of noradrenaline release by reversal of the Na+/Ca2+ exchanger and depolarization in chromaffin cells

We compared the effectiveness of Ca2+ entering by Na+/Ca2+ exchange with that of Ca2+ entering by channels produced by membrane depolarization with K+ in inducing catecholamine release from bovine adrenal chromaffin cells. The Ca2+ influx through the Na+/Ca2+ exchanger was promoted by reversing the normal inward gradient of Na+ by preincubating the cells with ouabain to increase the intracellular Na+ and then removing Na+ from the external medium. In this way we were able to increase the cytosolic free Ca2+ concentration ([Ca2+]c) by Na+/Ca2+ exchange to 325 +/- 14 nM, which was similar to the rise in [Ca2+]c observed upon depolarization with 35 mM K+ of cells not treated with ouabain. After incubating the cells with ouabain, K+ depolarization raised the [Ca2+]c to 398 +/- 31 nM, and the recovery of [Ca2+]c to resting levels was significantly slower. Reversal of the Na+ gradient caused an approximately 6-fold increase in the release of noradrenaline or adrenaline, whereas K+ depolarization induced a 12-fold increase in noradrenaline release but only a 9-fold increase in adrenaline release. The ratio of noradrenaline to adrenaline release was 1.24 +/- 0.23 upon reversal of the Na+/Ca2+ exchange, whereas it was 1.83 +/- 0.19 for K+ depolarization. Reversal of the Na+/Ca2+ exchange appeared to be as efficient as membrane depolarization in inducing adrenaline release, in that the relation of [Ca2+]c to adrenaline release was the same in both cases. In contrast, we found that for the same average [Ca2+]c, the Ca2+ influx through voltage-gated channels was much more efficient than the Ca2+ entering through the Na+/Ca2+ exchanger in inducing noradrenaline release from chromaffin cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The sigma compounds 1,3-di-o-tolylguanidine and N-allylnormetazocine inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells

Muscarine stimulated a concentration-dependent accumulation of [3H]inositol phosphates in bovine adrenal medullary cells preloaded with [3H]inositol. This muscarinic activation of inositol phospholipid metabolism was fully inhibited by the sigma-ligand 1,3-di-o-tolylguanidine (DTG) with an IC50 of approximately 45 microM. Higher concentrations (100 microM) of (+) N-allylnormetazocine (SKF-10047) also partially inhibited this response. A concentration of DTG sufficient to fully inhibit the muscarinic response also produced a significant partial inhibition of [3H]inositol phosphate accumulation in response to histamine but not to angiotensin II. These data demonstrate that sigma-compounds inhibit agonist-stimulated inositol phospholipid metabolism in bovine adrenal medullary cells, with a degree of selectivity towards the muscarinic response.

Calcium efflux from cultured bovine adrenal chromaffin cells induced by bradykinin

The effect of bradykinin on Ca2+ efflux from cultured bovine adrenal chromaffin cells was examined. Bradykinin enhanced the efflux of 45Ca2+ from the cells in a concentration dependent manner (10(-9)-10(-6) M). This effect was inhibited by a specific bradykinin B2-receptor antagonist, but not by a B1-receptor antagonist. Nifedipine, Co2+ and Cd2+ did not inhibit the bradykinin-stimulated 45Ca2+ efflux from the cells. 12-O-Tetradecanoyl phorbol 13-acetate, an activator of protein kinase C, also had no effect on the efflux of 45Ca2+ from the cells. The increase in bradykinin-stimulated 45Ca2+ efflux was reduced by removal of extracellular Na+. These results suggest that bradykinin stimulates Na+/Ca2+ exchange in cultured bovine adrenal chromaffin cells.

Single-cell fura-2 microfluorometry reveals different purinoceptor subtypes coupled to Ca2+ influx and intracellular Ca2+ release in bovine adrenal chromaffin and endothelial cells

ATP and adenosine(5')tetraphospho(5')adenosine (Ap4A), released from adrenal chromaffin cells, are potent stimulators of endothelial cell function. Using single-cell fura-2 fluorescence recording techniques to measure free cytosolic Ca2+ concentration ([Ca2+]i), we have investigated the role of purinoceptor subtypes in the activation of cocultured chromaffin and endothelial cells. ATP evoked concentration-dependent [Ca2+]i rises (EC50 = 3.8 microM) in a subpopulation of chromaffin cells. Both ATP-sensitive and -insensitive cells were potently activated by nicotine, bradykinin and muscarine. Reducing extracellular free Ca2+ concentration to around 100 nM suppressed the [Ca2+]i transient evoked by ATP but not the [Ca2+]i response to bradykinin. ATP-sensitive chromaffin cells were also potently stimulated by 2-methylthioadenosine triphosphate (2MeSATP; EC50 = 12.5 microM) and UTP, but did not respond to either adenosine 5'-[beta-thio]diphosphate (ADP[beta S]), a P2Y receptor agonist, adenosine 5'-[alpha,beta-methylene]triphosphate (pp-[CH2]pA), a P2X agonist or AMP. Adrenal endothelial cells displayed concentration-dependent [Ca2+]i responses when stimulated with ATP (EC50 = 0.86 microM), UTP (EC50 = 1.6 microM) and 2MeSATP (EC50 = 0.38 microM). 2MeSATP behaved as a partial agonist. Ap4A and ADP[beta S] also raised the [Ca2+]i in endothelial cells, whereas AMP and pp[CH2]pA were ineffective. Lowering extracellular free Ca2+ to around 100 nM did not affect the peak ATP-evoked [Ca2+]i rise in these cells. It is concluded that different purinoceptor subtypes are heterogeneously distributed among the major cell types of the adrenal medulla. An intracellular Ca(2+)-releasing P2U-type purinoceptor is specifically localized to adrenal endothelial cells, while a subpopulation of chromaffin cells expresses a non-P2X, non-P2Y subtype exclusively coupled to Ca2+ influx.

Histamine H1 receptor activation mediates the preferential release of adrenaline in the rat adrenal gland

Histamine elicited the release of catecholamines from "in vitro" perfused rat adrenals with an EC50 of 3 microM. This concentration was in the same range as those which caused a fall in the arterial blood pressure when infused intravenously in anaesthetized rats. Histamine stimulation was potently blocked by dexclorfeniramine (IC50 = 300 pM), but unaffected by ranitidine, suggesting the involvement of H1 receptors. Histamine release preferentially adrenaline. Mast cells were not detected within adrenal medulla by histochemical techniques. Compound 48/80 did not trigger catecholamine release. Catecholamine secretion evoked by splanchnic nerves stimulation was not modified by a combination of H1 and H2 antagonists. In conclusion, the histamine that elicited adrenaline release from rat adrenals comes from blood circulation not from local mast cells or splanchnic nerves. These effects are mediated through the activation of H1 receptors.

Secretogranin II: regulation of synthesis and post-translational proteolysis in bovine adrenal chromaffin cells

Secretogranin II (SgII), also called chromogranin C, is an acidic tyrosine-sulfated secretory protein found in secretory granules in a wide variety of endocrine cells and neurones. Although less abundant than chromogranin A (CGA) and chromogranin B (CGB), SgII is found in adrenal medullary chromaffin granules. In the present study we investigated the regulation of SgII biosynthesis in bovine chromaffin cells maintained in primary culture. Cellular proteins were labelled with [35S]methionine and the heat stable chromogranin enriched fraction was isolated. Following electrophoretic separation, the 86 kDa SgII band was identified by sequence analysis using the Edman degradation procedure. The radioactivity incorporated in the 86 kDa SgII band was used as an index of the SgII synthesis rate. We found that stimulation of chromaffin cells with nicotine and histamine and to a smaller extent with angiotensin II and bradykinin significantly enhanced the rate of SgII synthesis. In contrast direct depolarization with K+ may not be sufficient to induce modifications in SgII synthesis suggesting that the raise of cytosolic calcium evoked by high K+ may not be sufficient to induce modifications in SgII synthesis . The possible second messenger pathways involved in the control of SgII biosynthesis were investigated by using protein kinase C and adenylate cyclase activators. We observed that 12-O-tetradecanoylphorbol 13-acetate (TPA) and forskolin increased the basal rate of SgII synthesis. Incubation with both TPA and forskolin was required to obtain an effect comparable to that produced by nicotine or histamine suggesting that these secretagogues recruit both protein kinase C- and cyclic AMP-dependent mechanisms to stimulate SgII synthesis.

Pertussis toxin enhances proenkephalin synthesis in bovine chromaffin cells

The synthesis of the neuropeptide precursor proenkephalin was measured in bovine adrenal chromaffin cells following radiolabeling with [35S]methionine. Treatment of chromaffin cells with pertussis toxin (100 ng/ml) approximately doubled proenkephalin synthesis without altering total protein synthesis. Pertussis toxin pretreatment also increased proenkephalin synthesis in chromaffin cells exposed to vasoactive intestinal peptide (VIP) and 3-isobutyl-1-methylxanthine (IBMX). Combinations of IBMX plus nicotine, VIP, or histamine also synergistically enhanced proenkephalin synthesis, with no further elevation when the cells were also pretreated with pertussis toxin. The action of forskolin, a direct activator of adenylate cyclase, on proenkephalin synthesis was similarly potentiated by pertussis toxin or IBMX, presumably reflecting the abilities of both the toxin and this phosphodiesterase inhibitor to enhance the cyclic AMP response to forskolin. In contrast, increased synthesis of proenkephalin in response to phorbol esters was not affected by pertussis toxin treatment. These results suggest that pertussis toxin potentiates proenkephalin synthesis primarily through inactivation of guanine nucleotide-binding proteins that inhibit adenylate cyclase, although other signaling pathways may also be involved.

Endogenous histamine in cultured bovine adrenal chromaffin cells

Histamine releases catecholamines and opioids in primary cultured bovine adrenal medullary (BAM) chromaffin cells. We have studied whether histamine is synthesized and localized in BAM cells, and whether it can be released upon activation with secretagogues. In BAM cells histamine is immunohistochemically co-localized with tyrosine hydroxylase in 45 +/- 8% of all cells. Only histamine immunoreactivity was observed in 8 +/- 2% of all BAM cells. No mast-cell-like cells were observed in our system. Histamine can be released from BAM cells by high potassium (56 mM K+) in a calcium-dependent manner. Compound 48/80 did not release histamine from BAM cells but nicotine caused a dose-dependent liberation of the amine. Cultured BAM cells have histidine decarboxylase activity which is inhibited by alpha-fluoromethylhistidine. These results indicate that endogenous histamine is synthesized, stored and released in BAM chromaffin cells in vitro.

Ionic mechanisms involved in the secretory effects of histamine in the rat adrenal medulla

Histamine activation of H1 receptors elicited the release of adrenaline from in vitro perfused rat adrenal with an EC50 of 3 microM. Neither Na+ deprivation nor complete membrane depolarization abolished the histamine-mediated secretory response but it was partially dependent on extracellular Ca2+. Nitrendipine and BAY-K-8644 affected the release induced by histamine concentrations at over 3 microM. Delayed application of histamine pulses, after external Ca2+ removal, led to a decline in to a plateau at 50% of the initial release. Pretreatment with ionomycin abolished this Ca2+ deprivation-resistant component. These data suggest that secretion evoked by low concentrations of histamine occurs by mobilization of Ca2+ from internal stores whereas higher concentrations use Ca2+ from both intracellular and extracellular sources.

Spatial localization of agonist-induced Ca2+ entry in bovine adrenal chromaffin cells. Different patterns induced by histamine and angiotensin II, and relationship to catecholamine release

The spatial organization of agonist-induced Ca2+ entry in single bovine adrenal chromaffin cells has been investigated using video-imaging techniques to visualize fura-2 quenching by the Ca2+ surrogate, Mn2+. The potent secretagogue histamine, in addition to releasing Ca2+ from intracellular stores, resulted in a large influx of external Mn2+ that occurred over the entire surface of the cell. The influx of Ca2+ that this mirrors was found to be an obligatory requirement for the triggering of catecholamine release by histamine, which suggests that such a global influx of Ca2+ into the cell probably underlies the ability of this agonist to stimulate a large secretory response. By contrast, the weaker secretagogue angiotensin II, which also acts through the second messenger inositol trisphosphate, produced a localized entry of external Mn2+ in 64% of cells. In these cells, localized Mn2+ entry always occurred at the pole of the cell in which the angiotensin II-induced rise in [Ca2+]i was largest. Since exocytosis in response to angiotensin II has previously been shown to be restricted to this same pole of the cell (Cheek et al. (1989). J. Cell Biol. 109, 1219–1227), these results suggest that localized influx of Ca2+ in response to angiotensin II could underlie the polarized exocytotic response observed with this stimulus. These results directly demonstrate that different agonists can induce different patterns of divalent cation influx in the same cells and, furthermore, suggest how these different patterns can have a direct influence on cellular function.

Histamine evokes greater increases in phosphatidylinositol metabolism and catecholamine secretion in epinephrine-containing than in norepinephrine-containing chromaffin cells

Chromaffin cells have H1 histamine receptors. Histamine, acting at these receptors, increases the metabolism of inositol-containing phospholipids and stimulates catecholamine secretion from chromaffin cells. We have investigated the effects of histamine and other agents on the accumulation of inositol monophosphate (InsP1) and catecholamine secretion in purified cultures of norepinephrine-containing and epinephrine-containing bovine chromaffin cells. Histamine-stimulated InsP1 accumulation in epinephrine cells was three times greater than that in norepinephrine cells. In contrast, bradykinin caused roughly equivalent increases in InsP1 accumulation in the two chromaffin cell subtypes. Histamine-stimulated catecholamine secretion was also greater in epinephrine cells than in norepinephrine cells, whereas high K+, bradykinin, phorbol 12,13-dibutyrate, and angiotensin II all caused greater secretion from norepinephrine cells than from epinephrine cells. The density of H1 receptors in epinephrine cells was approximately three times greater than that in norepinephrine cells. The greater density of H1 receptors on epinephrine cells may account for the greater effects of histamine on InsP1 accumulation and catecholamine secretion in these cells.

Role of omega-conotoxin GVIA-sensitive Ca2+ entry in angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding in bovine adrenal medullary cells

The relative contributions of Ca2+ influx and intracellular Ca2+ mobilization were examined for angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding, which reflects the level of activated protein kinase C in bovine chromaffin cells. Angiotensin II receptors activate phospholipase C in chromaffin cells, leading to a short-lived mobilization of intracellular Ca2+. Angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding was largely blocked in Ca(2+)-free buffer and by pretreatment with the Ca(2+)-channel blocker omega-conotoxin GVIA. The [3H]phorbol 12,13-dibutyrate binding response to [Sar1]angiotensin II also appeared to be voltage sensitive, as no additivity was observed with the response to the depolarizing agent 4-aminopyridine (3 mM). Threshold sensitivities of the extra- and intracellular Ca(2+)-mobilizing pathways to angiotensin II were similar, and all examined effects of angiotensin II in these cells were apparently mediated by losartan-sensitive (AT1-like) receptors. The dependence of angiotensin II-stimulated [3H]phorbol 12,13-dibutyrate binding on extracellular Ca2+ entry, in contrast to stimulation by other phospholipase C-linked receptor agonists (bradykinin and methacholine), suggests that angiotensin II preferentially stimulates protein kinase C translocation to the plasma membrane, rather than to internal membranes, in bovine adrenal medullary cells.

Small-conductance Ca(2+)-activated K+ channels in bovine chromaffin cells

Simultaneous whole-cell patch-clamp and fura-2 fluorescence [Ca2+]i measurements were used to characterize Ca(2+)-activated K+ currents in cultured bovine chromaffin cells. Extracellular application of histamine (10 microM) induced a rise of [Ca2+]i concomitantly with an outward current at holding potentials positive to -80 mV. The activation of the current reflected an increase in conductance, which did not depend on membrane potential in the range -80 mV to -40 mV. Increasing the extracellular K+ concentration to 20 mM at the holding potential of -78 mV was associated with inwardly directed currents during the [Ca2+]i elevations induced either by histamine (10 microM) or short voltage-clamp depolarizations. The current reversal potential was close to the K+ equilibrium potential, being a function of external K+ concentration. Current fluctuation analysis suggested a unit conductance of 3-5 pS for the channel that underlies this K+ current. The current could be blocked by apamin (1 microM). Whole-cell current-clamp recordings showed that histamine (10 microM) application caused a transient hyperpolarization, which evolved in parallel with the [Ca2+]i changes. It is proposed that a small-conductance Ca(2+)-activated K+ channel is present in the membrane of bovine chromaffin cells and may be involved in regulating catecholamine secretion by the adrenal glands of various species.

Evidence for a nucleotide receptor on adrenal medullary endothelial cells linked to phospholipase C and phospholipase D

1. We have investigated whether the 'atypical' P2-purinoceptor previously described on adrenal microvasculature endothelial cells is a nucleotide receptor (responds to pyrimidines and purines) and is linked to phospholipase D as well as phospholipase C. 2. Cultured bovine adrenal medullary endothelial (BAME) cells responded to the pyrimidine UTP, as well as the purines. The total [3H]-inositol phosphate responses were with a rank order of UTP > ATP- = adenosine 5'-O-(3-thio-triphosphate) (ATP gamma S) >> 2MeSATP. The selective P2x agonist beta, gamma-methylene ATP was inactive. 3. Construction of dose-response curves to ATP, ATP gamma S and UTP in the presence and absence of additional agonists showed that responses to ATP gamma S and UTP were not additive, nor were those to UTP and ATP. This suggests that purines and pyrmidines acted via a common nucleotide receptor. 4. 32P-labelled BAME cells, in the presence of butanol, produced [32P]-phosphatidylbutanol (PBut) when stimulated with ATP gamma S or the protein kinase C activator, tetradecanoyl phorbol acetate (TPA). 5. Cells labelled with [3H]-palmitate and stimulated in the presence of butanol generated [3H]-PBut with the same order of agonist potencies seen for inositol phosphate responses. 6. The protein kinase C inhibitor, Ro 31-8220, abolished TPA and agonist stimulation of [3H]-PBut production. 7. These observations, and our related studies on bovine aortic endothelial cells, provide the first demonstration of a phospholipase C linked nucleotide receptor on vascular endothelial cells. It is concluded that BAME cells express a nucleotide receptor linked to phospholipase C and phospholipase D, but that activation of phospholipase D is probably down-stream of phospholipase C.