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Growth factors in chromaffin cells.

Chromaffin cells, the neuroendocrine cells of the adrenal medulla and paraganglia, occupy paradigmatic roles in molecular, cellular and developmental neurobiology. The fact that they are very effective 'minipumps', secreting numerous bioactive substances including amines, neuropeptides and proteins, has made them interesting and useful for the treatment of chronic pain and Parkinsonism. An essential advantage of chromaffin cells is that they can be isolated and purified in extremely high numbers, which can never be achieved for peripheral or central nervous system neurons. Growth factors (cytokines) and peptides with growth factor-like efficacies constitute an important component of bioactive materials released from chromaffin cells. Not only their presence, but also neural and humoral mechanisms regulating their expression and release, are now being revealed. Prominent examples include fibroblast growth factors (FGFs), transforming growth factor-beta s (TGF-beta s) and interleukins. Functions that can be assigned to these factors in the adrenal medulla are gradually emerging. For example, FGFs and TGF-beta s can regulate chromaffin cell proliferation and differentiation and participate in the neurotrophic maintenance of neurons innervating chromaffin cells. In contrast, the functions of the predominant secretory proteins of chromaffin cells, the chromogranins, are still largely unknown, but might include cytokine-like roles. Thus, chromaffin cells continue to teach neurobiologists about the fundamental capacity of neurons to secrete bioactive molecules with a wide range of functions as well as modes of their secretion underscoring the close relationship of endocrine and neuronal systems.

Adrenal Medulla↗

AP-1-related proteins bind to the enkephalin CRE-2 element in adrenal chromaffin cells.

Chromaffin cells of the adrenal medulla are neural crest-derived neuroendocrine cells that express neuropeptide genes in vivo and in vitro. As such these cells are useful for examining tissue- and cell-specific regulation of the enkephalin gene. We previously demonstrated that the chromatin configuration of the enkephalin gene correlated with its tissue-specific expression in the adrenal medulla and primary chromaffin cell cultures. In this study we examine and characterize binding of transcription factors to the enkephalin promoter/enhancer region. Gel shift analyses of this region with extracts from chromaffin cells and PC12 cells (a pheochromocytoma cell line that does not express the enkephalin gene) demonstrate that all detectable binding is to ENKCRE-2, a cyclic AMP response-like element, and that the binding is cell specific. Gel shift and supershift analyses show that, unlike reports demonstrating that binding activity in the CNS is composed of the cyclic AMP response element binding protein, CREB, the majority of protein binding in chromaffin cells is from the AP-1 family of transcription factors. This binding is composed of c-Jun, JunD, and possibly a novel Fos-related protein(s). These data suggest enkephalin gene expression in the adrenal gland is controlled by cell-specific binding of transcription factors from the Fos/Jun families to the enkephalin CRE-2 element. Furthermore, these data suggest at least two different modes of enkephalin gene regulation exist between endocrine and neuronal tissues.

Adrenal Glands↗

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.

Adrenal Glands↗

Cholinergic regulation of protein phosphorylation in bovine adrenal chromaffin cells.

Chromaffin cells were isolated from bovine adrenal medullae and maintained in primary culture. After prelabeling with 32PO4, exposure of the chromaffin cells to acetylcholine increased the phosphorylation of a Mr approximately equal to 100,000 protein and a Mr approximately equal to 60,000 protein (tyrosine hydroxylase), visualized after separation of total cellular proteins in naDodSO4/polyacrylamide gels. Immunoprecipitation with antibodies to three known phosphoproteins ("100-kDa," "87-kDa," and protein III) revealed an acetylcholine-dependent phosphorylation of these proteins. These three proteins were also shown to be present in bovine adrenal chromaffin cells by immunolabeling techniques. "100-kDa" is a Mr approximately equal to 100,000 protein selectively phosphorylated by calcium/calmodulin-dependent protein kinase III, "87-kDa" is a Mr approximately equal to 87,000 protein selectively phosphorylated by protein kinase C, and protein III is a phosphoprotein doublet of Mr approximately equal to 74,000 (IIIa) and Mr approximately equal to 55,000 (IIIb) phosphorylated by cAMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase I. Furthermore, 100-kDa was shown to be identical to the Mr approximately equal to 100,000 protein whose phosphorylation was increased by acetylcholine treatment. The acetylcholine-dependent increase in phosphorylation of tyrosine hydroxylase, 100-kDa, 87-kDa, and protein III required extracellular calcium and was mimicked by nicotine, veratridine, elevated K+, and calcium ionophore A23187, but not by muscarine. In addition, forskolin increased the phosphorylation of tyrosine hydroxylase, 100-kDa, and protein III, but not that of 87-kDa. Phorbol 12,13-dibutyrate increased the phosphorylation of tyrosine hydroxylase, 87-kDa, and protein III, but not that of 100-kDa. The data demonstrate that cholinergic activation of chromaffin cells increases the phosphorylation of several proteins and that several protein kinase systems may be involved in these effects.

Acetylcholine↗

Alpha-melanocyte stimulating hormone promotes neurite outgrowth in chromaffin cells.

Chromaffin cells from adult bovine adrenal medulla were found to develop neurites when cocultured with pituitary intermediate lobe (IL) cells. In coculture 51.7% of the chromaffin cells extended neurites compared with 12% in control cultures (chromaffin cells alone). A soluble factor released by IL cells was apparently involved as medium conditioned by contact with IL cells also promoted neurite outgrowth. Moreover, the addition of alpha MSH, one of the pro-opiomelanocortin-derived peptides secreted by IL cells, alone reproduced this effect in a dose-dependent manner. The data provide evidence for a neurotrophic role of alpha MSH.

Adrenal Medulla↗

Coexpression of cloned alpha(1B), beta(2a), and alpha(2)/delta subunits produces non-inactivating calcium currents similar to those found in bovine chromaffin cells.

Chromaffin cells express N-type calcium channels identified on the basis of their high sensitivity to block by omega-conotoxin GVIA (omega-CgTx GVIA). In contrast to neuronal N-type calcium currents that inactivate during long depolarizations and that require negative holding potentials to remove inactivation, many chromaffin cells exhibit N-type calcium channel currents that show little inactivation during maintained depolarizations and that exhibit no decrease in channel availability at depolarized holding potentials. N-type calcium channels are thought to be produced by combination of the pore-forming alpha(1B) subunit and accessory beta and alpha(2)/delta subunits. To examine the molecular composition of the non-inactivating N-type calcium channel, we cloned the alpha(1B) and accessory beta (beta(1b), beta(1c,) beta(2a), beta(2b), and beta(3a)) subunits found in bovine chromaffin cells. Expression of the subunits in either Xenopus oocytes or human embryonic kidney 293 cells produced high-threshold calcium currents that were blocked by omega-CgTx GVIA. Coexpression of bovine alpha(1B) with beta(1b), beta(1c), beta(2b), or beta(3a) produced currents that were holding potential dependent. In contrast, coexpression of bovine alpha(1B) with beta(2a) produced holding potential-independent calcium currents that closely mimicked native non-inactivating currents, suggesting that non-inactivating N-type channels consist of bovine alpha(1B), alpha(2)/delta, and beta(2a).

Alternative Splicing↗

Differential regulation of phenylethanolamine N-methyltransferase expression in two distinct subpopulations of bovine chromaffin cells.

Chromaffin cells were isolated from bovine adrenal glands and fractionated into two distinct subpopulations by density gradient centrifugation on Percoll. Cells in the more dense fraction stored epinephrine (E) as their predominant catecholamine (81% of total catecholamines), contained high levels of phenylethanolamine N-methyltransferase (PNMT) activity, and exhibited intense PNMT immunoreactivity. This population of chromaffin cells was termed the E-rich cell population. Cells in the less dense fraction, the norepinephrine (NE)-rich cell population, stored predominantly NE (75% of total catecholamines). Although the NE-rich cells had only 3% as much PNMT activity as did the E-rich cells, 20% of the NE-rich cells were PNMT immunoreactive. This suggested that the PNMT-positive cells in the NE-rich cell cultures contained less PNMT per cell than did E-rich cells and may not be typical adrenergic cells. The regulation of PNMT mRNA levels and PNMT activity in primary cultures of E-rich and NE-rich cells was compared. At the time the cells were isolated, PNMT mRNA levels in NE-rich cells were approximately 20% of those in E-rich cells; within 48 h in culture, PNMT mRNA in both populations declined to almost undetectable levels. Treatment with dexamethasone increased PNMT mRNA levels and PNMT activity in both populations. In E-rich cells, dexamethasone restored PNMT mRNA to the level seen in freshly isolated cells and increased PNMT activity twofold. In NE-rich cells, dexamethasone increased PNMT mRNA to levels twice those found in freshly isolated cells and increased PNMT activity sixfold. Cycloheximide blocked the effects of dexamethasone on PNMT mRNA expression in NE-rich cells but had little effect in E-rich cells. Angiotensin II, forskolin, and phorbol 12,13-dibutyrate elicited large increases in PNMT mRNA levels in E-rich cells but had no effect in NE-rich cells. Our data suggest that PNMT expression is regulated differently in the two chromaffin cell subpopulations.

Adrenal Glands↗

Anti-alpha-fodrin inhibits secretion from permeabilized chromaffin cells.

Chromaffin cells release catecholamine- and peptide-containing granules by exocytosis, by a mechanism involving movement of secretory granules towards the cell membrane, their apposition to it and the fusion of the granule membrane with the plasma membrane. One of the two subunits of membrane-associated brain spectrin, alpha-fodrin is an actin-binding protein which is found at the periphery of chromaffin cells and may be involved in secretion. Because cultured chromaffin cells can be permeabilized with detergents, giving pores large enough to permit the entry of immunoglobulin molecules, we used permeabilized cells to test the effect of specific antibodies on secretory mechanisms. Incubation of permeabilized cells with polyclonal immunoaffinity-purified monospecific anti-alpha-fodrin antibody or its Fab fragments did not modify basal release but did specifically inhibit Ca2+-induced catecholamine release by exocytosis. Our observations indicate that fodrin and the cytoskeleton participate in the release mechanism.

Adrenal Medulla↗

Differential regulation of natriuretic peptide biosynthesis in bovine adrenal chromaffin cells.

Chromaffin cells synthesize and secrete two forms of natriuretic peptides which are also found in the heart and in the central nervous system. While atrial tissue predominantly contains atrial natriuretic factor (ANF), brain tissue appears to produce relatively larger amounts of brain natriuretic peptide (BNP) also identified as aldosterone secretion inhibitory factor (ASIF), suggesting tissue-specific differential regulation of these two peptides. This report compares the modulation of the biosynthesis and secretion of ASIF with that of ANF using cultured chromaffin cells as a model system. Cholinergic nicotinic activation and KCl depolarization induce a 5-fold increase of the corelease of ASIF and pro-ASIF in cell culture medium concomitantly with a 3-fold stimulation of ANF and pro-ANF cosecretion. While the combined treatment with phorbol ester and forskolin produces a 2-fold increase in total ANF level, it induces a synergistic 20-fold elevation of total ASIF level. These results indicate that chromaffin cell secretagogues induce the cosecretion of both the precursor and mature forms of ASIF and ANF. The preferential stimulation of ASIF production is revealed by the combined treatment rendering the ASIF to ANF proportion similar to that in brain.

Adrenal Medulla↗

Phosphotyrosine phosphatase activity associated with c-Src in large multimeric complexes isolated from adrenal medullary chromaffin cells.

Chromaffin cells, which secrete catecholamines in response to acetylcholine, express high levels of the Src-family tyrosine kinases. These kinases contain protein-protein interaction domains which bind signal transduction proteins that participate in a variety of cellular processes. To determine if signalling proteins bind c-Src in chromaffin cells, we examined c-Src immunocomplexes for co-precipitating proteins. We discovered a phosphotyrosine phosphatase (PTPase; EC 3.1.3.48) activity which associates with specific subcellular pools of c-Src in vivo and which preferentially binds the SH2 (Src homology 2) domain of c-Src in vitro. Known PTPases were not identified by blotting of c-Src immunocomplexes with a panel of anti-PTPase antibodies, suggesting that the PTPase may be a novel family member. The c-Src-PTPase complex is enriched in the plasma membrane fraction and exists in several large complexes, as revealed by gel-filtration analysis. This PTPase activity is altered rapidly following stimulation by secretagogues, decreasing within 30 s and returning to basal levels by 60 s of stimulation. Both the subcellular localization and rapid activity changes suggest that the c-Src-associated PTPase may function in early signalling events emanating from the nicotinic acetylcholine receptor. In support of this is the co-precipitation of a PTPase activity with the nicotinic acetylcholine receptor and co-chromatography of this receptor with one or the c-Src-PTPase complexes.

Adrenal Medulla↗

Mechanism of calcium efflux from isolated bovine adrenal chromaffin cells.

Chromaffin cells isolated from bovine adrenals and maintained in culture were loaded with 45Ca, and the mechanism of 45Ca efflux from these cells was investigated. During exposure to a Ca-deficient, Mg (1 mM)-containing medium, replacement of NaCl with sucrose, choline Cl, or Tris Cl reduced the rate of 45Ca efflux by approx. 30-40%, showing the presence of a Na-dependent 45Ca efflux mechanism. In contrast to the previous findings, however, Li can partially replace Na in maintaining 45Ca efflux. Reintroduction of Ca to a Ca-deficient medium increased the rate of 45Ca efflux depending on the concentrations of Ca, showing the presence of a Ca-dependent Ca efflux mechanism. The marked but transient rise in the rate of 45Ca efflux in response to Ca reintroduction was observed under conditions in which the concentration of internal Na was raised either by inhibiting Na pumping activity (ouabain or K removal) or by removal of Mg from the medium. The increased 45Ca efflux was further potentiated by simultaneous Na removal and was markedly inhibited by Ca channel blockers, suggesting that the transiently increased Ca influx in exchange for internal Na facilitated the rate of 45Ca efflux. However, other conditions which evoke catecholamine secretion by stimulating Ca influx also increased the rate of 45Ca efflux, suggesting that the increased Ca influx via any route increases 45Ca efflux. These results thus confirmed the presence of both Na-dependent and Ca-dependent Ca efflux mechanisms in chromaffin cells.

Adrenal Medulla↗

Muscarinic release of inositol trisphosphate without mobilization of calcium in bovine adrenal chromaffin cells.

Chromaffin cells of bovine adrenal medulla release catecholamines in response to activation of nicotinic ACh receptors which open voltage-sensitive calcium channels. Catecholamine secretion by exocytosis requires an increase in cytosolic free calcium. The cells also possess muscarinic ACh receptors but muscarinic agents do not provoke catecholamine release. Quin-2 studies show that they do not increase cytosolic free Ca2+ concentration, but unlike the nicotinic agents, they cause phosphoinositide hydrolysis. Muscarinic stimulation leads to rapid loss of labelled phosphatidylinositol 4-phosphate and of phosphatidylinositol 4,5-bisphosphate. At the same time there is release of inositol trisphosphate, inositol bisphosphate and inositol phosphate. In a number of other cells inositol trisphosphate may act as a second messenger releasing Ca2+ from storage sites in the endoplasmic reticulum but this is not its function in bovine chromaffin cells.

Adrenal Medulla↗

Studies on the effect of insulin-like growth factor-I on catecholamine secretion from chromaffin cells.

Chromaffin cells cultured in serum-free medium secreted a smaller percentage of their catecholamine stores in response to stimulation by high K+ (55 mM) than did cells cultured in serum-containing medium. Addition of insulin-like growth factor-I (IGF-I) to serum-free medium restored high K(+)-stimulated catecholamine secretion to the levels seen in serum-treated cultures. In contrast, addition of IGF-I to serum-containing medium had little effect on catecholamine secretion. These results suggest that serum contains IGF-I or another factor that maintains the secretory responsiveness of chromaffin cells. IGF-I not only enhanced high K(+)-stimulated catecholamine secretion, but also augmented secretion elicited by the nicotinic agonist dimethyl-phenylpiperazinium, the dihydropyridine agonist Bay K 8644, and Ba2+. IGF-I did not affect the dependence of catecholamine secretion on extracellular Ca2+ concentration nor did it affect the time course of secretion. Experiments using 45Ca2+ demonstrated that IGF-I treatment enhanced Ca2+ uptake into the cells. When cells were permeabilized by treatment with digitonin, Ca2(+)-dependent catecholamine secretion was slightly, but consistently, greater from IGF-I-treated cells than from untreated cells. Our results suggest that IGF-I may enhance catecholamine secretion partly by increasing Ca2+ entry into the cells and partly by affecting a step distal to Ca2+ entry.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

Pituitary adenylate cyclase-activating polypeptide stimulates both adrenocortical cells and chromaffin cells in the frog adrenal gland.

In a previous report, we have shown that frog pituitary adenylate cyclase-activating polypeptide (fPACAP38) is a potent stimulator of corticosteroid secretion by frog adrenal slices in vitro. The aim of the present study was to determine the mode of action of PACAP on the frog adrenal gland. Immunoelectron microscopic labeling revealed that PACAP-like immunoreactivity is present in electron-dense vesicles within nerve endings located in the vicinity of both adrenocortical and chromaffin cells. Exposure of dispersed adrenal cells to fPACAP38 caused stimulation of corticosteroid secretion. Labeling of cultured adrenal cells with [125I]PACAP27 revealed the existence of PACAP-binding sites on both adrenocortical and chromaffin cells. Saturation and competition experiments showed the occurrence of high affinity and selective receptors for fPACAP38 on cultured adrenal cells. fPACAP38 (10(-8)-10(-5) M) provoked a dose-dependent stimulation of cAMP production by frog adrenal slices. Microflurimetric studies demonstrated that fPACAP38 induced a substantial elevation of the intracellular calcium concentration in both adrenocortical and chromaffin cells. The present results indicate that in the frog adrenal gland, PACAP fibers innervate both adrenocortical and chromaffin cells. The data show the presence of PACAP receptors on the two cell types. PACAP exerts a direct stimulatory effect on corticosteroid-producing cells. This effect is probably mediated through stimulation of adenylyl cyclase activity and/or augmentation of intracellular Ca2+. PACAP also increases intracellular Ca2+ in chromaffin cells. These data suggest that PACAP, released locally in the adrenal gland, acts as a neuroendocrine factor, regulating the activity of adrenocortical and chromaffin cells.

Adrenal Cortex↗

Cografting with polymer-encapsulated human nerve growth factor-secreting cells and chromaffin cell survival and behavioral recovery in hemiparkinsonian rats.

Encapsulated cell grafting is one approach for the delivery of neurotransmitters and/or neurotrophic factors to the brain. Baby hamster kidney (BHK) cells were genetically modified to secrete high levels of human nerve growth factor (hNGF). Following polymer encapsulation, these cells were implanted into the left lateral ventricle or the left striatum 1.5 mm away from striatally cografted unencapsulated adrenal medullary chromaffin cells in hemiparkinsonian rats. Although the animals receiving adrenal medulla alone or adrenal medulla with intraventricular hNGF-secreting cell grafting did not show recovery of apomorphine-induced rotational behavior, the animals receiving adrenal medulla with intrastriatal hNGF-secreting cell implants showed a significant recovery of rotational behavior 2 and 4 weeks after transplantation. Histological analysis revealed that in animals receiving adrenal medulla with intraventricular hNGF-secreting cell grafting, the number of tyrosine hydroxylase-immunoreactive (TH-IR) surviving chromaffin cells tended to be higher (approximately five to six times) than in animals receiving adrenal medulla alone; however, this increase did not reach statistical significance. In contrast, in animals receiving adrenal medullary cells together with intrastriatal hNGF-secreting cells, the number of TH-IR surviving chromaffin cells was more than 20 times higher than that in animals receiving adrenal medullary cells alone. Analysis of retrieved capsules revealed that hNGF continued to be released by encapsulated BHK-hNGF cells after 4 weeks in vivo. Moreover, histological analysis confirmed the presence of numerous viable encapsulated BHK-hNGF cells. These results indicate the potential use of intrastriatal implantation of encapsulated hNGF-secreting cells for augmenting the survival of cografted chromaffin cells as well as promoting the functional recovery of hemiparkinsonian rats. These data indicate that this approach may have potential application for treating Parkinson's disease.

Animals↗

Cholinergic stimulants and excess potassium ion increase the fluidity of plasma membranes isolated from adrenal chromaffin cells.

Chromaffin cell membranes from the bovine adrenal medulla were labelled with the hydrophobic fluorescent probe 1,6-diphenyl-1,3,5-hexatriene, and the fluorescence polarization (P) of the membrane suspensions was measured as a function of temperature. The P versus t profiles, between 20 and 37 degrees C, showed two linear regions separated by a break in the vicinity of 30 degrees C, reflecting a change in the phase behaviour of the constitutent lipids. Decreases in P values at higher temperature indicated progressive fluidization of the lipid bilayer. Previous incubation with either acetylcholine (0.5 mM) or nicotine (50 microM) produced further fluidization, the extent of which depended on the presence of added Ca2+ (2.2 mM). Thus, the flow activation energy, delta E, between approx. 30 and 37 degrees C was 9.1 kcal/mol for acetylcholine and 8.8 kcal/mol for acetylcholine plus Ca2+, as compared to 7.9 kcal/mol in the absence of acetylcholine and Ca2+. In the presence of nicotine, delta E was 11.4 kcal/mol when Ca2+ was absent and 9.5 kcal/mol when it was present. The cholinergic blocker, hexamethonium (0.5 mM), abolished the acetylcholine- or nicotine-induced changes. 65 mM K+ produced a similar fluidization, which was reversed by addition of Ca2+. An additive effect was observed when the membranes were incubated with both nicotine and K+, with delta E = 16.6 kcal/mol in the presence of Cas2+. These results indicate a receptor-mediated modulation of the lipid distribution between rigid and fluid regions in the membrane, which could be of importance for stimulated catecholamine secretion in the intact cell.

Acetylcholine↗

Quantitative analysis of exocytosis directly visualized in living chromaffin cells.

Chromaffin cells isolated from the bovine adrenal medulla were observed under a Nomarski microscope through a CCD camera and an image processor. Exocytotic events of individual granules including fusion, extrusion, swelling, omega-figure formation, and membrane retrieval were visualized in individual cells stimulated by acetylcholine or K-rich solution. Initial steps were quicker than 16 ms, and the membrane retrieval was slower than 1-60 s. These findings provided a light microscopic proof for the exocytosis hypothesis as well as a basis for quantification of hormonal release. The technique was used to demonstrate significant secretion induced by a muscarinic agonist.

Acetylcholine↗

Nerve growth factor effect on adenosine transport in cultured chromaffin cells.

Chromaffin cells both recently isolated or in culture present a high-affinity adenosine transporter with a Km value of 1 microM. When cells were exposed to nerve growth factor (NGF; 10 ng/ml), the adenosine transporter affinity decreased to 3 microM. This value was maintained from 3 days after plating to the end of the culture period. A change in the transport capacity was observed, with a significant increase (approximately 200-260%) in NGF-cultured cells throughout the period studied.

Adenosine↗