Adrenomedullary and glycemic alterations following diverse stress in soft-shelled turtles Lissemys punctata punctata Bonnoterre

The objective of the current investigation was to study adrenomedullary and glycemic responses to stress in soft-shelled turtles, Lissemys p. punctata. Dehydration (7 days) and formalin (formaldehyde 1%, 0.1 mL/100 g body wt. daily for 7 days) stress-stimulated adrenomedullary activity at histological (by increasing the nuclear diameter and degranulation of chromaffin cells) and hormonal levels (by elevations of norepinephrine and epinephrine concentrations) with hyperglycemia in turtles. But salt loading (NaCl: 1%, 1 mL/100 g body wt. daily for 7 days) had no significant effect on adrenomedullary activity or glycemia presumably owing to the nonresponsiveness of adrenocortical activity to salt stress in turtles. It is suggested that dehydration and formalin stresses might have exerted their actions through the hypothalamo (CRF)-hypophysial (ACTH)-adrenocortical axis in turtles.

Adenoviral gene transfer in bovine adrenomedullary and murine pheochromocytoma cells: potential clinical and therapeutic relevance

Recombinant adenoviruses (rAd) have been widely used as gene transfer vectors both in the laboratory and in human clinical trials. In the present study, we investigated the effects of adenoviral-mediated gene transfer in primary bovine adrenal chromaffin cells (BACC) and a murine pheochromocytoma cell line (MPC). Cells were infected with one of three nonreplicating E1/E3-deleted (E1(-)/E3(-)) rAd vectors: Ad.GFP, expressing a green fluorescent protein (GFP); Ad.null, expressing no transgene; or Ad.C2.TK, expressing the herpes simplex virus-1 thymidine kinase gene (TK). Forty-eight hours after exposure to Ad.GFP, the percentage of GFP-expressing BACC ranged from 23.5-97% in a dose-dependent manner and similarly from 1.06-84.4% in the MPC, indicating that adrenomedullary cells are a potentially valuable target for adenoviral-mediated gene transfer. Ultrastructural analysis, however, revealed profound changes in the nucleus and mitochondria of cells infected with rAd. Furthermore, infection of BACC with Ad.null was accompanied by a time- and dose-dependent decrease in cell survival due to the vector alone. Specific whole-cell norepinephrine uptake was also decreased in a time- and dose-dependent fashion in BACC. Infection of MPC cells with the Ad.C2.TK vector sensitized them to the cytotoxic effect of the antiviral drug ganciclovir, in direct proportion to the fraction of cells infected with the virus. We conclude that rAd may alter the structural and functional integrity of adrenomedullary cells, potentially interfering with the normal stress response. At the same time, in light of their ability to effectively deliver and express genes in pheochromocytoma cells, they may be applicable to the gene therapy of adrenomedullary tumors.

Exocytotic catecholamine release is not associated with cation flux through channels in the vesicle membrane but Na+ influx through the fusion pore

Release of charged neurotransmitter molecules through a narrow fusion pore requires charge compensation by other ions. It has been proposed that this may occur by ion flow from the cytosol through channels in the vesicle membrane, which would generate a net outward current. This hypothesis was tested in chromaffin cells using cell-attached patch amperometry that simultaneously measured catecholamine release from single vesicles and ionic current across the patch membrane. No detectable current was associated with catecholamine release indicating that <2% of cations, if any, enter the vesicle through its membrane. Instead, we show that flux of catecholamines through the fusion pore, measured as an amperometric foot signal, decreases when the extracellular cation concentration is reduced. The results reveal that the rate of transmitter release through the fusion pore is coupled to net Na+ influx through the fusion pore, as predicted by electrodiffusion theory applied to fusion-pore permeation, and suggest a prefusion rather than postfusion role for vesicular cation channels.

Glycogen synthase kinase 3 activation is essential for the snake phospholipase A2 neurotoxin-induced secretion in chromaffin cells

Neuroendocrine chromaffin cells were used to study the mechanism of the snake phospholipase A2 (PLA2) neurotoxin enhancement of exocytosis. Notexin, beta-bungarotoxin, taipoxin or textilotoxin enhanced the fast release of catecholamines elicited by flash photolysis of cytosolic caged calcium. Such an increase correlates with the capacity of these neurotoxins to cause fragmentation of the F-actin cortical barrier with subsequent accumulation of vesicles in the proximity of the plasma membrane. These PLA2 neurotoxins do not act via protein kinase C activation, which is known to promote F-actin fragmentation. Lithium, RO31-8220 and SB216763, three inhibitors of the glycogen synthase kinase 3, prevent both the alteration of the F-actin peripheral cortex and the enhancement of fast release elicited by these neurotoxins. In addition, glycogen synthase kinase 3 has been detected by immunolocalization in a membranous compartment of the chromaffin cell endoplasmic reticulum (ER). These results suggest that the activation of this enzyme plays a major role in the enhancement of exocytosis of the readily releasable granules caused by PLA2 neurotoxins in neuroendocrine chromaffin cells.

Serotonin (5-hydroxytryptamine, 5-HT) immunoreactive endocrine and neural elements in the chromaffin enteropancreatic system of amphibians and reptiles

The diffuse chromaffin enteropancreatic system of nine species of amphibians (newts, frogs) and reptiles (turtles, lizards, snakes) was investigated immunohistochemically for the presence and topographic distribution of serotonin (5-hydroxytryptamine, 5-HT). The study revealed various numbers of serotonin-producing cells in the pancreas and intestinal epithelium and also immunolabelled nerve profiles in the villi of all species studied. In addition, two different morphological populations of serotonin cells ("open" and "closed") were localized in the functional segments of the intestines in the representative species of all the taxa investigated. Semi-quantitative evaluation of the immunolabelled pancreatic and enteric cells revealed significantly different mean numbers of labelled cells in different amphibian and reptilian taxa, and also between the various successive gut segments of each taxon. The ratio between "open" and "closed" varieties of serotonin cells recorded along the intestines followed a decreasing trend, progressive in lizards and snakes and more abrupt in newts, frogs and turtles. The above findings may help resolve several key stages of the phylogenetic evolution of poikilothermic vertebrates.

Ca2+-dependent activator protein for secretion 1 is critical for constitutive and regulated exocytosis but not for loading of transmitters into dense core vesicles

Although CAPS1 was originally identified as a soluble factor that reconstitutes Ca(2+)-dependent secretion from permeabilized neuroendocrine cells, its exact function in intact mammalian cells remains controversial. Here we investigate the role for CAPS1 by generating stable cell lines in which CAPS1 is strongly down-regulated. In these cells, Ca(2+)-dependent secretion was strongly reduced not only of catecholamine but also of a transfected neuropeptide. These secretion defects were rescued by infusion of CAPS1-containing brain cytosol or by transfection-mediated expression of CAPS1. Whole cell patch clamp recording revealed significant reductions in slow burst and sustained release components of exocytosis in the knockdown cells. Unexpectedly, they also accumulated higher amounts of endogenous and exogenous transmitters, which were attributable to reductions in constitutive secretion. Electron microscopy did not reveal abnormalities in the number or docking of dense core vesicles. Our results indicate that CAPS1 plays critical roles not only in Ca(2+)-dependent, regulated exocytosis but also in constitutive exocytosis downstream of vesicle docking. However, they do not support the role for CAPS1 in loading transmitters into dense core vesicles.

Cadmium stimulates MAPKs and Hsp27 phosphorylation in bovine adrenal chromaffin cells

Cadmium (Cd(2+)) is a common environmental pollutant, which is widely used in industry and is a constituent of tobacco smoke. Exposure to this heavy metal has been linked to a wide range of detrimental effects on mammalian cells. In this study, the action of Cd(2+) on protein phosphorylation in bovine adrenal chromaffin cells (BACCs) was examined. Cells were incubated with (32)Pi in the presence of Cd(2+) (1-50 microM) and proteins were separated by one- or two-dimensional electrophoresis. An increase in the phosphorylation of BACCs proteins, without changing cell viability, was observed in response to Cd(2+) (5-50 microM). Particularly at three spots, with molecular weight of 25kDa and isoeletric point range 4.0-4.5, which were identified as phosphorylated isoforms of the heat shock protein of 27kDa (Hsp27). Phosphorylation of the p38(MAPK), a member of mitogen-activated protein kinase (MAPK) family, was stimulated by Cd(2+) over the same concentration range and it was the major upstream protein kinase involved in the phosphorylation of all three spots of Hsp27. Cd(2+) also stimulated the phosphorylation of other MAPK family member, the extracellular signal-regulated kinase (ERK)-1/2. Therefore, primary adrenal chromaffin cells are a target for Cd(2+) and both the ERK1/2 and the p38(MAPK) are activated. Additionally, Hsp27 is highly phosphorylated in response to the metal exposure, due to p38(MAPK) activation. These biochemical effects of Cd(2+) might disrupt the normal secretory function of these cells.

On-chip amperometric measurement of quantal catecholamine release using transparent indium tin oxide electrodes

Carbon-fiber amperometry has been extensively used to monitor the time course of catecholamine release from cells as individual secretory granules discharge their contents during the process of quantal exocytosis, but microfabricated devices offer the promise of higher throughput. Here we report development of a microchip device that uses transparent indium tin oxide (ITO) electrodes to measure quantal exocytosis from cells in microfluidic channels. ITO films on a glass substrate were patterned as 20-mum-wide stripes using photolithography and wet etching and then coated with polylysine to facilitate cell adherence. Microfluidic channels (100 mum wide by 100 mum deep) were formed by molding poly(dimethylsiloxane) (PDMS) on photoresist and then reversibly sealing the PDMS slab to the ITO-glass substrate. Bovine adrenal chromaffin cells were loaded into the microfluidic channel and adhered to the ITO electrodes. Cells were stimulated to secrete by perfusing a depolarizing "high-K" solution while monitoring oxidation of catecholamines on the ITO electrode beneath the cell using amperometry. Amperometric spikes with charges ranging from 0.1 to 1.5 pC were recorded with a signal-to-noise ratio comparable to that of carbon-fiber electrodes. Further development of this approach will enable high-throughput measurement of quantal catecholamine release simultaneously with optical cell measurements such as fluorescence.

Proteomics of neuroendocrine secretory vesicles reveal distinct functional systems for biosynthesis and exocytosis of peptide hormones and neurotransmitters

Regulated secretory vesicles produce, store, and secrete active peptide hormones and neurotransmitters that function in cell-cell communication. To gain knowledge of the protein systems involved in such secretory vesicle functions, we analyzed proteins in the soluble and membrane fractions of dense core secretory vesicles purified from neuroendocrine chromaffin cells. Soluble and membrane fractions of these vesicles were subjected to SDS-PAGE separation, and proteins from systematically sectioned gel lanes were identified by microcapillary LC-MS/MS (microLC-MS/MS) of tryptic peptides. The identified proteins revealed functional categories of prohormones, proteases, catecholamine neurotransmitter metabolism, protein folding, redox regulation, ATPases, calcium regulation, signaling components, exocytotic mechanisms, and related functions. Several novel secretory vesicle components involved in proteolysis were identified consisting of cathepsin B, cathepsin D, cystatin C, ubiquitin, and TIMP, as well carboxypeptidase E/H and proprotein convertases that are known to participate in prohormone processing. Significantly, the membrane fraction exclusively contained an extensive number of GTP nucleotide-binding proteins related to Rab, Rho, and Ras signaling molecules, together with SNARE-related proteins and annexins that are involved in trafficking and exocytosis of secretory vesicle components. Membranes also preferentially contained ATPases that regulate proton translocation. These results implicate membrane-specific functions for signaling and exocytosis that allow these secretory vesicles to produce, store, and secrete active peptide hormones and neurotransmitters released from adrenal medulla for the control of physiological functions in health and disease. In summary, this proteomic study illustrates secretory vesicle protein systems utilized for the production and secretion of regulatory factors that control neuroendocrine functions.

Temperature-dependent differences between readily releasable and reserve pool vesicles in chromaffin cells

Statistical differences between amperometric traces recorded from chromaffin cells using K(+) and Ba(2+) secretagogues support the assertion that readily releasable pool (RRP) and reserve pool (RP) vesicles can be probed with pool-specific secretagogues. Release from the RRP was evoked by K(+) while release from the RP was evoked by Ba(2+). Similar temperature-dependent changes in spike area and half-width for both pools suggest that the content of RRP and RP vesicles is similar and packaged in the same way. Differences between the vesicle pools were revealed in the temperature dependence of spike frequency. While the burst spike frequency of the RRP, which is comprised of pre-docked and primed vesicles, increased 2.8% per degrees C, the RP spike frequency increased 12% per degrees C. This difference is attributed to a temperature-dependent mobilization of the RP. Furthermore, the RP exhibited more foot events at room temperature than the RRP but this difference was not apparent at 37 degrees C. This trend suggests that RP vesicle membranes have a compromised surface tension compared to RRP vesicles. Collectively, the changes of release characteristics with temperature reveal distinctions between the RRP and the RP.

Facilitation of quantal release induced by a D1-like receptor on bovine chromaffin cells

Dopaminergic receptors are found on bovine adrenal chromaffin cells and have been implicated in the facilitation of an inward calcium current [Artalejo et al., (1990) Nature 348, 239-242] that could enhance release. However, previous studies using incubations of long duration (minutes) with dopaminergic receptor antagonists have found instead an inhibition of catecholamine release. In this work we used brief (subsecond) chemical depolarizing stimuli to reexamine the role of dopaminergic receptors on exocytosis from bovine adrenal chromaffin cells. Responses to consecutive depolarizing stimuli were compared using amperometry to monitor vesicular release events and intracellular fura-2 to examine Ca2+ dynamics within individual cells. Restoration of intracellular Ca2+ levels to their initial values following exposure to 60 mM K+ was found to be prolonged unless the exposure was brief (0.5 s) and the cells were maintained at 37 degrees C. However, with these optimum conditions, a second stimulation evoked more exocytotic events than the first. This effect was blocked by SCH-23390, a D1 antagonist, in a dose dependent fashion, but not by raclopride, a D2 antagonist. The D1 agonist, SKF-38393, enhanced the number of exocytotic events as did prior exposure of the cell to epinephrine. Taken together, the data indicate that released catecholamines can enhance their own release by interaction with a D1-like receptor on bovine adrenal chromaffin cells.

Desensitized nicotinic receptors that, however, afford cytoprotection in bovine chromaffin cells

Neuronal nicotinic receptors for acetylcholine (nAChRs) are among the ionotropic receptors that suffer the most desensitization upon prolonged exposure to their agonists. This is particularly true for the alpha7 subtype of nAChRs, although alpha3beta4 receptors also suffer quick desensitization. This study was planned to test the hypothesis that even after suffering desensitization, a given nAChR might still afford cell protection against a noxious stimulus. Of the many agonists developed for nAChRs, we selected the poorly desensitizing ligand dimethylphenylpiperazinium (DMPP) (Britt and Brenner, 1997) and the highly desensitizing agent epibatidine (EPB) (Marks et al., 1996). We have measured nAChR currents, catecholamine secretory responses, and changes of [Ca2+]c elicited by stimulation of nAChRs with DMPP or EPB. We have also investigated cytoprotection elicited by DMPP and EPB against the cytotoxic effects of veratridine in bovine chromaffin cells.

Age-dependent regulation of chromaffin cell proliferation by growth factors, dehydroepiandrosterone (DHEA), and DHEA sulfate

The adrenal gland comprises two endocrine tissues of distinct origin, the catecholamine-producing medulla and the steroid-producing cortex. The inner adrenocortical zone, which is in direct contact with the adrenomedullary chromaffin cells, produces dehydroepiandrostendione (DHEA) and DHEA sulfate (DHEAS). These two androgens exhibit potential effects on neurogenesis, neuronal survival, and neuronal stem cell proliferation. Unlike the closely related sympathetic neurons, chromaffin cells are able to proliferate throughout life. The aim of this study was to investigate the effect of DHEA and DHEAS on proliferation of bovine chromaffin cells from young and adult animals. We demonstrated that graded concentrations of leukemia inhibitory factor induced proliferation of chromaffin cells from young animals, whereas EGF had no effect. On the contrary, EGF increased the cell proliferation in cells from adult animals, whereas leukemia inhibitory factor was inactive. In both cases, DHEA decreased the proliferative effect induced by the growth factors. Surprisingly, DHEAS enhanced, in a dose-dependent-manner, the effect of growth factors on proliferation in cells from adult animals but not from young animals. Flutamide, ICI 182,780, and RU 486 had no effect on the action of DHEA or DHEAS on chromaffin cell proliferation. These data show that DHEA and its sulfated form, DHEAS, differentially regulate growth-factor-induced proliferation of bovine chromaffin cells. In addition, the sensitivity of chromaffin cells to different growth factors is age-dependent. Furthermore, these two androgens may act through a receptor other than the classical steroid receptors.

Measurements of membrane patch capacitance using a software-based lock-in system

On-cell patch-clamp capacitance measurements can resolve the fusion of individual vesicles to a membrane patch and the accompanying dilation of the fusion pore. So far, these measurements have used a patch-clamp amplifier in combination with a hardware lock-in amplifier. Usually, solely the capacitance and conductance outputs of hardware lock-in amplifiers were recorded, which needed to be filtered rather heavily to suppress spectral components at the stimulus frequency. Therefore, the temporal resolution was limited, and information carried in the patch current was not utilized. In this paper, we describe an alternative and more versatile approach for measuring patch capacitance and conductance, using a digitally controlled patch-clamp amplifier. The software lock-in system showed better bandwidth and identical signal-to-noise performance needing less instrumentation. High temporal resolution measurements on patches of chromaffin cells showed that vesicle fission can be completed in only tens of microseconds. Capacitance calculation based on the patch current allows for straightforward offline phase correction. Moreover, the close inspection of direct current for the first time revealed small current changes accompanying the fusion and fission of large secretory vesicles, promising new insights into the vesicles' membrane properties. A practical guide to high-resolution on-cell patch-clamp capacitance measurements using the software lock-in is provided.

Enhancement of secretion by threshold nicotinic stimulation in bovine chromaffin cells

Synaptic release of neurotransmitters displays activity-dependent changes such as enhancement (facilitation, augmentation, or potentiation) or diminution (depression), which have been studied widely because of their implication in synaptic efficacy, neuronal plasticity, and formation and consolidation of learning and memory. Some of these types of modulation of secretion displayed by neurons are also present in neuroendocrine chromaffin cells, for instance, facilitation or augmentation, which seem to be related to mild changes in the transients of cytosolic concentration of calcium ([Ca2+]i) and the degree of refilling of the primed vesicle pool (Zucker, 1996; Neher, 1998). Desensitized nicotinic acetylcholine receptors (nAChRs) and their possible role in this short-term synaptic plasticity was investigated in populations of bovine chromaffin cells.

Role of DHEA and growth factors in chromaffin cell proliferation

Dehydroepiandrostreone (DHEA) is a neuroactive steroid produced by the inner layer of the adrenal cortex close to the adrenomedullary cells. Chromaffin cell growth and proliferation are under the control of insulin-like growth factor II (IGF-II) and basic fibroblast growth factor (bFGF). The aim of the present study was to examine the role of DHEA on chromaffin cell proliferation induced by IGF-II and bFGF. In our model, DHEA significantly decreased IGF-II-induced proliferation by 48.7%, whereas it did not affect the proliferation induced by bFGF. These data suggest that DHEA exerts a paracrine function in the control of chromaffin cell growth.

Intrathecal Implants of Microencapsulated Xenogenic Chromaffin Cells Provide a Long-Term Source of Analgesic Substances

Adrenal medullary chromaffin cells secrete several neuroactive substances including catecholamines and opioid peptides that produce analgesic effects in the central nervous system. This study was designed to investigate whether intrathecal microencapsulated chromaffin cells could release analgesic materials producing antiallodynic effects on the chronic neuropathic pain in rats induced by chronic constriction injury (CCI) of the sciatic nerve. Prior to intrathecal implantation, chromaffin cells were encapsulated with alginate and poly-L-lysine to protect them from the host immune system. Behavior tests were performed before CCI, 1 week later, and at 4, 7, 14, 21, 28 days postimplantation. At the end of study, we performed cerebrospinal fluid (CSF) collection and implant retrieval. We observed that intrathecal implantation of encapsulated xenogenic chromaffin cells reduced the mechanical and cold allodynia in a model of neuropathic pain. CSF levels of catecholamines and metenkephalin in the rats that received implants were higher than the controls. In addition, we observed chronic survival of implants. These results suggested that intrathecal microencapsulated chromaffin cells may represent a new approach to chronic neuropathic pain management.

A simple and rapid HPLC-MS method for the simultaneous determination of epinephrine, norepinephrine, dopamine and 5-hydroxytryptamine: application to the secretion of bovine chromaffin cell cultures

This method simultaneously determines epinephrine, norepinephrine, dopamine and 5-hydroxytryptamine by HPLC coupled to atmospheric pressure chemical ionization mass spectrometry, using bovine chromaffin cells to test xenobiotic neurotoxicity and the secretion alterations of these neurotransmitters as endpoint. Chromatographic separation was developed by injecting the sample without previous treatment into a reversed-phase column. The signal was recorded in selected ion mode. The lowest limit of detection was found for hydroxytryptamine, while the highest limit was for norepinephrine. The feasibility of the proposed method was checked by performing measurements of neurotransmitters during the assessment the effect of mipafox on the basal and potassium-induced secretions of chromaffin cell cultures.

Chromaffin cells in the adrenal homolog ofAphanius fasciatus (teleost fish) express piecemeal degranulation in response to osmotic stress: A hint for a conservative evolutionary process

The effect of severe osmotic stress on the ultrastructural morphology of chromaffin cells in the adrenal homolog of Aphanius fasciatus, a small eurhyaline teleost living in saltpans, was evaluated by electron microscopy quantitative analysis. Fishes were transferred from salt water, whose salinity was 3.7%, to dechlorinated tap water and chromaffin cells were studied at resting condition and after 2 and 48 hr from the beginning of the experiment. Ultrastructural examination revealed a series of granule and cytoplasmic changes highly specific for piecemeal degranulation (PMD), a secretory process based on vesicular transport of cargoes from within granules for extracellular release, which was previously described in chromaffin cells of the mouse, rat, and human adrenal medulla. There was indeed a significant trend toward loss of content material from chromaffin granules accompanied by enlargement of granule size. Remarkably, chromaffin granules maintained their individual close structure during the whole releasing process and eventually transformed into large empty containers. A dramatic increase in the density of small, membrane-bound, variably electron-dense vesicles free in the cytoplasm or attached to granules was recognized during the first 2 hr of stress response. These features fell to control levels after 48 hr. A similar time-course pattern was observed concerning the formation of budding projections from the surface of chromaffin granules. This study provides new insight into PMD physiology and suggests that PMD is part of an adaptive secretory response to severe osmotic stress in fishes. From an evolutionary point of view, this study lends support to the concept that PMD is a secretory mechanism highly conserved throughout vertebrate classes.

Neuronal differentiation of PC12 cells abolishes the expression of membrane androgen receptors

Sex steroids affect adrenal chromaffin cell function. In the present work, we have examined the expression and functional significance of membrane androgen receptor sites in normal rat adrenal chromaffin cells and in the PC12 rat pheochromocytoma cell line which can differentiate to either a neuronal or to an epithelial phenotype and expresses membrane estrogen receptor sites. Our data are as follows: (a) no cytosolic androgen receptors were found in both normal chromaffin and PC12 cells; (b) both types of chromaffin cells expressed high affinity membrane testosterone binding sites; (c) activation of these sites increased cytosolic Ca(2+), decreased catecholamine secretion and induced apoptosis; (d) NGF-induced neuronal differentiation of PC12 cells resulted in the suppression of the number of membrane testosterone sites. In conclusion, our data provide evidence for the existence of specific membrane testosterone receptors on adrenal chromaffin cells via which androgens, (some of them originating in the cortex) modulate their function. Neuronal differentiation of chromaffin cells results in a significant attenuation of these effects, via suppression of the expression of membrane androgen receptors suggesting, that the latter are specific for epithelioid chromaffin cells.

Gata3 participates in a complex transcriptional feedback network to regulate sympathoadrenal differentiation

Gata3 mutant mice expire of noradrenergic deficiency by embryonic day (E) 11 and can be rescued pharmacologically or, as shown here, by restoring Gata3 function specifically in sympathoadrenal (SA) lineages using the human DBH promoter to direct Gata3 transgenic expression. In Gata3-null embryos, there was significant impairment of SA differentiation and increased apoptosis in adrenal chromaffin cells and sympathetic neurons. Additionally, mRNA analyses of purified chromaffin cells from Gata3 mutants show that levels of Mash1, Hand2 and Phox2b (postulated upstream regulators of Gata3) as well as terminally differentiated SA lineage products (tyrosine hydroxylase, Th, and dopamine beta-hydroxylase, Dbh) are markedly altered. However, SA lineage-specific restoration of Gata3 function in the Gata3 mutant background rescues the expression phenotypes of the downstream, as well as the putative upstream genes. These data not only underscore the hypothesis that Gata3 is essential for the differentiation and survival of SA cells, but also suggest that their differentiation is controlled by mutually reinforcing feedback transcriptional interactions between Gata3, Mash1, Hand2 and Phox2b in the SA lineage.

A rapid exocytosis mode in chromaffin cells with a neuronal phenotype

We have used astrocyte-conditioned medium (ACM) to promote the transdifferentiation of bovine chromaffin cells and study modifications in the exocytotic process when these cells acquire a neuronal phenotype. In the ACM-promoted neuronal phenotype, secretory vesicles and intracellular Ca2+ rise were preferentially distributed in the neurite terminals. Using amperometry, we observed that the exocytotic events also occurred mainly in the neurite terminals, wherein the individual exocytotic events had smaller quantal size than in undifferentiated cells. Additionally, duration of pre-spike current was significantly shorter, suggesting that ACM also modifies the fusion pore stability. After long exposure (7-9 days) to ACM, the kinetics of catecholamine release from individual vesicles was markedly accelerated. The morphometric analysis of vesicle diameters suggests that the rapid exocytotic events observed in neurites of ACM-treated cells correspond to the exocytosis of large dense-core vesicles (LDCV). On the other hand, experiments performed in EGTA-loaded cells suggest that ACM treatment promotes a better coupling between voltage-gated calcium channels (VGCC) and LDCV. Thus, our findings reveal that ACM promotes a neuronal phenotype in chromaffin cells, wherein the exocytotic kinetics is accelerated. Such rapid exocytosis mode could be caused at least in part by a better coupling between secretory vesicles and VGCC.

Regulation of alternative splicing of Slo K+ channels in adrenal and pituitary during the stress-hyporesponsive period of rat development

Stress triggers release of ACTH from the pituitary, glucocorticoids from the adrenal cortex, and epinephrine from the adrenal medulla. Although functions differ, these hormone systems interact in many ways. Previous evidence indicates that pituitary and steroid hormones regulate alternative splicing of the Slo gene at the stress axis-regulated exon (STREX), with functional implications for the calcium-activated K+ channels prominent in adrenal medullary and pituitary cells. Here we examine the role of corticosterone in Slo splicing regulation in pituitary and adrenal tissues during the stress-hyporesponsive period of early rat postnatal life. The sharp drop in plasma corticosterone (CORT) that defines this period offers a unique opportunity to test CORT's role in Slo splicing. We report that in both adrenal and pituitary tissues, the percentage of Slo transcripts having STREX declines and recovers in parallel with CORT. Moreover, addition of 500 nm CORT to cultures of anterior pituitary cells from 13-, 21-, and 30-d postnatal animals increased the percentage of Slo transcripts with STREX, whereas 20 microm CORT reduced STREX representation. Applied to adrenal chromaffin cells, 20 microm CORT decreased STREX inclusion, whereas neither 500 nm nor 2 microm had any effect. The mineralocorticoid receptor antagonist RU28318 abolished the effect of 500 nm CORT on splicing in pituitary cells, whereas the glucocorticoid receptor antagonist RU38486 blocked the effect of 20 microm CORT on adrenal chromaffin cells. These results support the hypothesis that the abrupt, transient drop in CORT during the stress-hyporesponsive period drives the transient decline in STREX splice variant representation in pituitary, but not adrenal.

Intersectin-1L nucleotide exchange factor regulates secretory granule exocytosis by activating Cdc42

Rho GTPases are key regulators of the actin cytoskeleton in membrane trafficking events. We previously reported that Cdc42 facilitates exocytosis in neuroendocrine cells by stimulating actin assembly at docking sites for secretory granules. These findings raise the question of the mechanism activating Cdc42 in exocytosis. The neuronal guanine nucleotide exchange factor, intersectin-1L, which specifically activates Cdc42 and is at an interface between membrane trafficking and actin dynamics, appears as an ideal candidate to fulfill this function. Using PC12 and chromaffin cells, we now show the presence of intersectin-1 at exocytotic sites. Moreover, through an RNA interference strategy coupled with expression of various constructs encoding the guanine nucleotide exchange domain, we demonstrate that intersectin-1L is an essential component of the exocytotic machinery. Silencing of intersectin-1 prevents secretagogue-induced activation of Cdc42 revealing intersectin-1L as the factor integrating Cdc42 activation to the exocytotic pathway. Our results extend the current role of intersectin-1L in endocytosis to a function in exocytosis and support the idea that intersectin-1L is an adaptor that coordinates exo-endocytotic membrane trafficking in secretory cells.

The synthesis, structural characterization, and receptor specificity of the alpha-conotoxin Vc1.1

The alpha-conotoxin Vc1.1 is a small disulfide-bonded peptide currently in development as a treatment for neuropathic pain. This study describes the synthesis, determination of the disulfide connectivity, and the determination of the three-dimensional structure of Vc1.1 using NMR spectroscopy. Vc1.1 was shown to inhibit nicotine-evoked membrane currents in isolated bovine chromaffin cells in a concentration-dependent manner and preferentially targets peripheral nicotinic acetylcholine receptor (nAChR) subtypes over central subtypes. Specifically, Vc1.1 is selective for alpha3-containing nAChR subtypes. The three-dimensional structure of Vc1.1 comprises a small alpha-helix spanning residues Pro6 to Asp11 and is braced by the I-III, II-IV disulfide connectivity seen in other alpha-conotoxins. A comparison of the structure of Vc1.1 with other alpha-conotoxins, taken together with nAChR selectivity data, suggests that the conserved proline at position 6 is important for binding, whereas a number of residues in the C-terminal portion of the peptide contribute toward the selectivity. The structure reported here should open new opportunities for further development of Vc1.1 or analogues as analgesic agents.