Bisphenol-A disruption of the endocrine pancreas and blood glucose homeostasis

The link between endocrine disruptors and altered blood glucose homeostasis has been recently suggested. Epidemiological studies have correlated levels of phthalates, dioxins and persistent organic pollutants with alterations of blood glucose homeostasis in humans. Environmentally relevant doses of the ubiquitous endocrine disruptor bisphenol-A (BPA) have profound effects on mice endocrine pancreas--an essential tissue involved in glucose metabolism. BPA exerts rapid non-genomic effects on insulin releasing beta-cells and glucagon releasing alpha-cells within freshly isolated islets of Langerhans. In vivo, a single BPA injection of 10 microg/kg rapidly increases plasma insulin and concomitantly decreases glycaemia. When mice were treated with BPA 100 microg/kg/day for 4 days, the environmental oestrogen produced an increase in beta-cell insulin content along with a post-prandial hyperinsulinaemia and insulin resistance. The results reviewed here demonstrate that doses well below the current lowest observed adverse effect level considered by the US-EPA, disrupt pancreatic beta-cell function producing insulin resistance in male mice. Therefore, this altered blood glucose homeostasis by BPA exposure may enhance the risk of developing type II diabetes.

Langerhans cell sarcoma in a patient who underwent transplantation

Langerhans cell sarcoma is a rare, aggressive tumour that may metastasize to many organs, likely leading to death of the patient within 1 year. We present the first case described in the literature in a patient who underwent transplantation.

In vitro molecular mechanisms of bisphenol A action

Bisphenol A (BPA, 2,2-bis (4-hydroxyphenyl) propane; CAS# 80-05-7) is a chemical used primarily in the manufacture of polycarbonate plastic, epoxy resins and as a non-polymer additive to other plastics. Recent evidence has demonstrated that human and wildlife populations are exposed to levels of BPA which cause adverse reproductive and developmental effects in a number of different wildlife species and laboratory animal models. However, there are major uncertainties surrounding the spectrum of BPA's mechanisms of action, the tissue-specific impacts of exposures, and the critical windows of susceptibility during which target tissues are sensitive to BPA exposures. As a foundation to address some of those uncertainties, this review was prepared by the "In vitro" expert sub-panel assembled during the "Bisphenol A: An Examination of the Relevance of Ecological, In vitro and Laboratory Animal Studies for Assessing Risks to Human Health" workshop held in Chapel Hill, NC, Nov 28-29, 2006. The specific charge of this expert panel was to review and assess the strength of the published literature pertaining to the mechanisms of BPA action. The resulting document is a detailed review of published studies that have focused on the mechanistic basis of BPA action in diverse experimental models and an assessment of the strength of the evidence regarding the published BPA research.

Glucose induces synchronous mitochondrial calcium oscillations in intact pancreatic islets

Mitochondria shape Ca(2+) signaling and exocytosis by taking up calcium during cell activation. In addition, mitochondrial Ca(2+) ([Ca(2+)](M)) stimulates respiration and ATP synthesis. Insulin secretion by pancreatic beta-cells is coded mainly by oscillations of cytosolic Ca(2+) ([Ca(2+)](C)), but mitochondria are also important in excitation-secretion coupling. Here, we have monitored [Ca(2+)](M) in single beta-cells within intact mouse islets by imaging bioluminescence of targeted aequorins. We find an increase of [Ca(2+)](M) in islet-cells in response to stimuli that induce either Ca(2+) entry, such as extracellular glucose, tolbutamide or high K(+), or Ca(2+) mobilization from the intracellular stores, such as ATP or carbamylcholine. Many cells responded to glucose with synchronous [Ca(2+)](M) oscillations, indicating that mitochondrial function is coordinated at the whole islet level. Mitochondrial Ca(2+) uptake in permeabilized beta-cells increased exponentially with increasing [Ca(2+)], and, particularly, it became much faster at [Ca(2+)](C)>2 microM. Since the bulk [Ca(2+)](C) signals during stimulation with glucose are smaller than 2 microM, mitochondrial Ca(2+) uptake could be not uniform, but to take place preferentially from high [Ca(2+)](C) microdomains formed near the mouth of the plasma membrane Ca(2+) channels. Measurements of mitochondrial NAD(P)H fluorescence in stimulated islets indicated that the [Ca(2+)](M) changes evidenced here activated mitochondrial dehydrogenases and therefore they may modulate the function of beta-cell mitochondria. Diazoxide, an activator of K(ATP), did not modify mitochondrial Ca(2+) uptake.

Role of cannabinoid CB2 receptors in glucose homeostasis in rats

Here we show that the activation of cannabinoid CB2 receptors improved glucose tolerance after a glucose load. Blockade of cannabinoid CB2 receptors counteracted this effect, leading to glucose intolerance. Since blockade of cannabinoid CB1 receptors mimics the actions of cannabinoid CB2 receptor agonists, we propose that the endocannabinoid system modulates glucose homeostasis through the coordinated actions of cannabinoid CB1 and CB2 receptors. We also describe the presence of both cannabinoid CB1 and CB2 receptor immunoreactivity in rat pancreatic beta- and non-beta-cells, adding the endocrine pancreas to adipose tissue and the liver as potential sites for endocannabinoid regulation of glucose homeostasis.

Genistein affects adipose tissue deposition in a dose-dependent and gender-specific manner

The soy isoflavone genistein targets adipose tissue and elicits physiological effects that may vary based on dietary intake. We hypothesized that the adipose effects of genistein are dose and gender dependent. Four-week-old C57BL/6 male and female mice received daily oral doses of genistein (50-200,000 microg/kg.d) or 17beta-estradiol (E2) (5 microg/kg.d) for 15 d or a diet containing 800 ppm genistein. Genistein increased epididymal and renal fat pad and adipocyte size at doses up to 50,000 microg/kg.d or at 800 ppm in the diet in males but not in females. The alteration in adipocity correlated with changes in peripheral insulin resistance. These treatments increased genistein serum concentrations from 35+/-6 to 103+/-26 nM 12 h after treatment and lowered plasma triglycerides and cholesterol levels. The 200,000 microg/kg.d genistein dose decreased adipose tissue weight similarly to E2. This genistein dose down-regulated estrogen receptor (beta more than alpha) and progesterone receptor expression and induced estrogen-dependent adipose differentiation factors; it did not change expression of the minimal consensus estrogen-responsive element in ERE-tK-LUC mice, which was positively modulated in other tissues (e.g. the lung). E2 down-regulated almost all examined adipogenic factors. Gene microarray analysis identified factors in fat metabolism and obesity-related phenotypes differentially regulated by low and high doses of genistein, uncovering its adipogenic and antiadipogenic actions. The lower dose induced the phospholipase A2 group 7 and the phospholipid transfer protein genes; the 200,000 microg/kg.d dose inhibited them. The antiadipogenic action of genistein and down-regulation of adipogenic genes required the expression of ERbeta. In conclusion, nutritional doses of genistein are adipogenic in a gender-specific manner, whereas pharmacological doses inhibited adipose deposition.

Rapid endocrine disruption: environmental estrogen actions triggered outside the nucleus

An exogenous substance is defined as an endocrine disrupter chemical (EDC) if it alters the function of the endocrine system provoking adverse health effects. Environmental estrogens are the most studied EDCs. They follow the same mechanisms of action as the gonadal hormone 17beta-estradiol. Up to now, the estrogenicity of environmental estrogenic pollutants has been based on the property of these compounds to bind to estrogen receptors (ERs), either ERalpha or ERbeta, and to act subsequently as transcription factors when binding to the estrogen response element (ERE) in the DNA. All the estrogenic bioassays currently used are based on this mechanism of action. New evidence indicates that the definition of estrogenicity for a chemical should take into account other estrogen receptors as well as new signaling pathways. These include the activation of additional transcription factors as well as the action of xenoestrogens through estrogen receptors located outside the nucleus: in the plasma membrane, mitochondria and probably the cytosol. Therefore, new estrogenic bioassays should be developed to include the novel concept of rapid endocrine disruption.

Glucose induces opposite intracellular Ca2+ concentration oscillatory patterns in identified alpha- and beta-cells within intact human islets of Langerhans

Homeostasis of blood glucose is mainly regulated by the coordinated secretion of glucagon and insulin from alpha- and beta-cells within the islets of Langerhans. The release of both hormones is Ca(2+) dependent. In the current study, we used confocal microscopy and immunocytochemistry to unequivocally characterize the glucose-induced Ca(2+) signals in alpha- and beta-cells within intact human islets. Extracellular glucose stimulation induced an opposite response in these two cell types. Although the intracellular Ca(2+) concentration ([Ca(2+)](i)) in beta-cells remained stable at low glucose concentrations, alpha-cells exhibited an oscillatory [Ca(2+)](i) response. Conversely, the elevation of extracellular glucose elicited an oscillatory [Ca(2+)](i) pattern in beta-cells but inhibited low-glucose-induced [Ca(2+)](i) signals in alpha-cells. These Ca(2+) signals were synchronic among beta-cells grouped in clusters within the islet, although they were not coordinated among the whole beta-cell population. The response of alpha-cells was totally asynchronic. Therefore, both the alpha- and beta-cell populations within human islets did not work as a syncitium in response to glucose. A deeper knowledge of alpha- and beta-cell behavior within intact human islets is important to better understand the physiology of the human endocrine pancreas and may be useful to select high-quality islets for transplantation.

Cannabinoid receptors regulate Ca(2+) signals and insulin secretion in pancreatic beta-cell

Insulin is the main hormone involved in the regulation of glycaemia, its impaired secretion is a hallmark of type I and type II diabetic individuals. Additionally, insulin is involved in lipogenesis and weight gain, provoking an anorexigenic action. The endocannabinoid system contributes to the physiological regulation of energy balance, food intake and lipid and glucose metabolisms. Despite that, an experimental link between the endocannabinoid system and the endocrine pancreas has not yet been described. Using quantitative real-time PCR and immunocytochemistry, we have demonstrated the existence of both CB1 and CB2 receptors in the endocrine pancreas. While the CB1 receptor is mainly expressed in non-beta-cells, the CB2 type exists in beta- and non-beta-cells within the islet. The endocannabinoid 2-arachidonylglycerol (2-AG) through CB2 receptors regulates [Ca(2+)](i) signals in beta-cells and as a consequence, it decreases insulin secretion. This effect may be a new component involved in the orexigenic effect of endocannabinoids and constitutes a potential target for pharmacologic manipulation of the energy balance.

Activation of cannabinoid CB1 receptors induces glucose intolerance in rats

Recent reports have described the presence of cannabinoid CB1 receptors in pancreatic islets. Here we show that administration of the endogenous cannabinoid anandamide or the selective cannabinoid CB1 receptor agonist Arachidonyl-2'-chloroethylamide (ACEA) results in glucose intolerance after a glucose load. This effect is reversed by the selective cannabinoid CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM251). These results suggest that targeting cannabinoid CB1 receptors may serve as new therapeutic alternatives for metabolic disorders such as diabetes.

The estrogenic effect of bisphenol A disrupts pancreatic beta-cell function in vivo and induces insulin resistance

The function of the pancreatic beta-cell is the storage and release of insulin, the main hormone involved in blood glucose homeostasis. The results in this article show that the widespread environmental contaminant bisphenol-A (BPA) imitates 17beta-estradiol (E2) effects in vivo on blood glucose homeostasis through genomic and nongenomic pathways. The exposure of adult mice to a single low dose (10 microg/kg) of either E2 or BPA induces a rapid decrease in glycemia that correlates with a rise of plasma insulin. Longer exposures to E2 and BPA induce an increase in pancreatic beta-cell insulin content in an estrogen-receptor-dependent manner. This effect is visible after 2 days of treatment and starting at doses as low as 10 microg/kg/day. After 4 days of treatment with either E2 or BPA, these mice developed chronic hyperinsulinemia, and their glucose and insulin tolerance tests were altered. These experiments unveil the link between environmental estrogens and insulin resistance. Therefore, either abnormal levels of endogenous estrogens or environmental estrogen exposure enhances the risk of developing type 2 diabetes mellitus, hypertension, and dyslipidemia.

Bioluminescence imaging of nuclear calcium oscillations in intact pancreatic islets of Langerhans from the mouse

The stimulus-secretion coupling for insulin secretion by pancreatic beta cells in response to high glucose involves synchronic cytosolic calcium oscillations driven by bursting electrical activity. Calcium inside organelles can regulate additional functions, but analysis of subcellular calcium signals, specially at the single cell level, has been hampered for technical constrains. Here we have monitored nuclear calcium oscillations by bioluminescence imaging of targeted aequorin in individual cells within intact islets of Langerhans as well as in the whole islet. We find that glucose generates a pattern of nuclear calcium oscillations resembling those found in the cytosol. Some cells showed synchronous nuclear calcium oscillations suggesting that the islet of Langerhans may also regulate the activation of Ca(2+)-responsive nuclear processes, such as gene transcription, in a coordinated, synchronic manner. The nuclear Ca(2+) oscillations are due to bursting electrical activity and activation of plasma membrane voltage-gated Ca(2+) channels with little or no contribution of calcium release from the intracellular Ca(2+) stores. Irregularities in consumption of aequorins suggests that depolarization may generate formation of steep Ca(2+) gradients in both the cytosol and the nucleus, but further research is required to investigate the role of such high [Ca(2+)] microdomains.

Oestradiol rapidly inhibits Ca2+ signals in ciliary neurons through classical oestrogen receptors in cytoplasm

Oestrogen plays a key role in a great variety of actions in the nervous system, either through classical or alternative pathways. The classical pathways are initiated after oestrogen binding to the oestrogen receptors ERalpha or ERbeta, which translocate from the cytoplasm to the nucleus and act there as transcription factors. Alternative pathways are initiated at the plasma membrane and cytoplasm, via binding to classical or non-classical ERs. Using isolated ciliary ganglion neurons from the chick embryo and Ca2+ imaging, we demonstrated that a 10-min exposure to 17beta-oestradiol reduces Ca2+ influx through the plasma membrane. This effect was not reproduced by oestradiol conjugated to bovine serum albumin, which does not cross the plasma membrane, indicating that 17beta-oestradiol was acting intracellularly. ERalpha was detected in the cytoplasm by immunostaining and its involvement in the regulation of Ca2+ influx by ICI182,780 inhibition. The phosphatidylinositol-3 kinase (Pi3-kinase) inhibitor wortmannin and the nitric oxide synthase (NOS) inhibitor Nomega-nitro-L-arginine methyl ester (L-NAME) both blocked the oestradiol effect. The oestradiol effect was reproduced by 8Br-cGMP and abolished in the presence of the cGMP-dependent protein kinase (PKG) inhibitor KT5823. Our study indicates that 17beta-oestradiol can regulate Ca2+ influx via PI3-kinase, NOS and PKG after activation of cytoplasmic ER.

Low doses of bisphenol A and diethylstilbestrol impair Ca2+ signals in pancreatic alpha-cells through a nonclassical membrane estrogen receptor within intact islets of Langerhans

Glucagon, secreted from pancreatic alpha-cells integrated within the islets of Langerhans, is involved in the regulation of glucose metabolism by enhancing the synthesis and mobilization of glucose in the liver. In addition, it has other extrahepatic effects ranging from lipolysis in adipose tissue to the control of satiety in the central nervous system. In this article, we show that the endocrine disruptors bisphenol A (BPA) and diethylstilbestrol (DES), at a concentration of 10(-9) M, suppressed low-glucose-induced intracellular calcium ion ([Ca2+]i) oscillations in alpha-cells, the signal that triggers glucagon secretion. This action has a rapid onset, and it is reproduced by the impermeable molecule estradiol (E2) conjugated to horseradish peroxidase (E-HRP). Competition studies using E-HRP binding in immunocytochemically identified alpha-cells indicate that 17beta-E2, BPA, and DES share a common membrane-binding site whose pharmacologic profile differs from the classical ER. The effects triggered by BPA, DES, and E2 are blocked by the G alpha i- and G alpha o-protein inhibitor pertussis toxin, by the guanylate cyclase-specific inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, and by the nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester. The effects are reproduced by 8-bromo-guanosine 3',5'-cyclic monophosphate and suppressed in the presence of the cGMP-dependent protein kinase inhibitor KT-5823. The action of E2, BPA, and DES in pancreatic alpha-cells may explain some of the effects elicited by endocrine disruptors in the metabolism of glucose and lipid.

Disentangling the molecular mechanisms of action of endogenous and environmental estrogens

The gonadal hormone 17beta-estradiol is involved in numerous cellular processes. In many cases, 17beta-estradiol actions are imitated by synthetic and natural chemicals in the environment. Their actions differ depending on the target tissue, the receptors involved and the molecular pathways activated. The plethora of estrogenic actions is triggered by different receptors and other specific structures that activate different signalling pathways. This amount of information may lead to a maze of effects triggered by endogenous and environmental estrogens that we intend to clarify in this review. Understanding the variety of estrogen receptors, their different locations and the signalling pathways activated by estrogenic ligands is fundamental for understanding the diversity of actions that estrogens have in different tissues and cells.

Estrogen and xenoestrogen actions on endocrine pancreas: from ion channel modulation to activation of nuclear function

17beta-Estradiol elicits a rapid opposite effect on [Ca2+]i in alpha- and beta-cells within intact islets of Langerhans. In beta-cells, physiological concentrations of the gonadal hormone decreases KATP channel activity in synergy with glucose, leading to a membrane depolarization that opens voltage-gated Ca2+ channels, potentiating Ca2+ signals. As a consequence insulin release is enhanced and transcription factor CREB is activated in a Ca(2+)-dependent manner. In glucagon-containing alpha-cells, 17beta-estradiol provokes the abolishment of Ca2+ oscillations generated by low glucose, a situation that should decrease glucagon release. In both types of cells the second messenger involved is cGMP. The estrogen receptor involved is located in the plasma membrane and has a pharmacological profile unrelated to classical estrogen receptors ERalpha and ERbeta. For that reason, it has been named non-classical membrane estrogen receptor (ncmER). Although the physiological roles of this receptor are still unknown, it may be implicated in the responses of the endocrine pancreas to the physiological and pathological changes of 17beta-estradiol.

Immunohistochemical FMRP studies in a full mutated female fetus

Fragile X syndrome (FXS) is the most common form of inherited mental retardation. Clinical manifestations are due to the absence of the FMRP protein. Affected patients have widely variable phenotypes which are more variable in females than males, presumable due to X inactivation. We report the expression pattern of FMRP in cerebral cortex and ovary in a control and a full-mutated female fetus. FMRP was expressed in mutated and control fetal tissues, although at different levels and patterns. Control fetal cerebral cortex showed FMRP expression in almost all cells, whereas the full mutation carrier showed FMRP positivity in roughly 50% of cortical cells without any specific pattern. In the ovary samples, FMRP expression was seen in all germ cells surrounded by FMRP-negative paragranulosa and interstitial cells. The Müllerian epithelium of the fetal Fallopian tube was continuously positive in the control case, whereas the full mutation carrier showed a discontinuous patchy pattern. Expression of homologue proteins FXR1P and FXR2P showed no differences between control and full mutation fetuses. The pattern of FMRP expression in full mutation carrier females is in agreement with a random X-inactivation in maturing fetal tissues. Immunohistochemical results on cerebral tissues provide a clue for the variation of mental affection among female carriers, depending not only on the number of cells devoid of FMRP, but also on the ultimate destination of those cells in sensitive or more silent location for a proper cerebral development.

Adenosquamous carcinoma of the head and neck: criteria for diagnosis in a study of 12 cases

AIMS

Adenosquamous carcinoma (ASC) of the head and neck is an unusual neoplasm in which a general consensus with regard to diagnostic criteria has not yet been reached. In this study we report the clinicopathological results of 12 ASCs, with special attention to their histological and immunohistochemical characteristics in order to define this neoplasm more precisely.

METHODS AND RESULTS

All the patients were male with a peak incidence in the sixth decade of life. The tumours were located most frequently in the larynx and oral cavity, followed by the nasal cavity and pharynx. ASCs had two distinct histological components. The most extensive one was an usual keratinizing squamous cell carcinoma, arising from the surface epithelium, where characteristically severe dysplasia or carcinoma in situ was found in all cases. The second component was an adenocarcinoma, usually displayed in the deepest areas of the tumour. Evidence of origin from salivary or seromucinous glands was not found. Immunohistochemical studies demonstrated in most cases positivity of glandular differentiated areas for carcinoembryonic antigen (CEA) (11/12), CK7 (9/12) and CAM5.2 (7/12), whereas the squamous cell component was unreactive or reacted only focally for these markers. High-molecular-weight cytokeratin 34BE12 was positive in both components and CK20 was always negative. All cases showed high expression of Ki67 antigen. Most of them had overexpression of p53 (8/12) and DNA aneuploidy (10/12). Fifty percent of patients with ASC died of disease after a mean period of 23 months (range 12-35 months).

CONCLUSIONS

ASC of the head and neck is an aggressive neoplasm that originates in the surface epithelium of the upper respiratory tract. Severe dysplasia or carcinoma in situ is usually found and its recognition helps to make the diagnosis. In addition to mucin stains, positive immunoreactivity for CEA, CK7 and CAM5.2 helps to identify the glandular component.

Novel players in pancreatic islet signaling: from membrane receptors to nuclear channels

Glucose and other nutrients regulate many aspects of pancreatic islet physiology. This includes not only insulin release, but also insulin synthesis and storage and other aspects of beta-cell biology, including cell proliferation, apoptosis, differentiation, and gene expression. This implies that in addition to the well-described signals for insulin release, other intracellular signaling mechanisms are needed. Here we describe the role of global and local Ca(2+) signals in insulin release, the regulation of these signals by new membrane receptors, and the generation of nuclear Ca(2+) signals involved in gene expression. An integrated view of these pathways should improve the present description of the beta-cell biology and provide new targets for novel drugs.

Estradiol modulates acetylcholine-induced Ca2+ signals in LHRH-releasing GT1-7 cells through a membrane binding site

Estrogen regulation of the female reproductive axis involves the rapid inhibition (< 30 min) of luteinizing hormone-releasing hormone (LHRH) secretion from hypothalamic neurons. This fast time-course suggests interactions with potential plasma membrane binding sites that could result in short-term effects on LHRH neurons. Because LHRH release is calcium dependent, we have studied the acute effects of 17beta-estradiol (E2) and estradiol-peroxidase (E-HRP) on the elevations of intracellular calcium ([Ca2+]i) induced by acetylcholine (ACh) in LHRH-producing GT1-7 cells. Exposure to ACh (1-100 micro m) induced transient increases of [Ca2+]i, whereas pretreatment with E2 or E-HRP (10 nm) for 2 min reduced this response by 50-60%. The effect was specific for E2 as neither 17alpha-estradiol (1 micro m) nor the synthetic antiestrogens ICI182 780 (1 micro m) or tamoxifen (1 micro m) elicited any change on the ACh-induced Ca2+ signal. Both the latency of the effect and the response to the membrane impermeant conjugate suggested a membrane-mediated mechanism. Such membrane binding sites for E2 in GT1-7 cells were demonstrated by visualizing the binding of E-HRP and estradiol-BSA-fluorescein isothiocyanate (E-BSA-FITC) conjugates. Competition studies showed that E-HRP binding was blocked by preincubation with E2, but not with 17alpha-E2, ICI182 780, tamoxifen or progesterone, indicating that the plasma membrane binding site is highly specific for E2 and exhibits a pharmacological profile different from classical estrogen receptors. We conclude that ACh-induced increase in [Ca2+]i in GT1-7 cells is modulated acutely by physiological E2 concentrations in a manner which is compatible with the existence of an estrogen-specific membrane binding site.

Bovine subcommissural organ displays spontaneous and synchronous intracellular calcium oscillations

The subcommissural organ (SCO) is an ependymal brain gland that secretes into the cerebrospinal fluid glycoproteins that polymerize, forming Reissner's fiber (RF). The SCO-RF complex seems to be involved in vertebrate nervous system development, although its role in adults is unknown. Furthermore, its physiology is still greatly undetermined, and little is known about the release control of SCO secretion and the underlying intracellular mechanisms. In this report, we show that up to 90% of 3-5-day-old in vitro SCO cells from both intact and partially-dispersed SCO explants displayed spontaneous cytosolic Ca2+ oscillations. The putative role of these spontaneous calcium oscillations in SCO secretory activity is discussed taking into consideration several previous findings. Two distinct subpopulations of SCO cells were detected, each one containing cells with synchronized calcium oscillations. A possible existence of different functional domains in SCO is therefore discussed. Oscillations persisted in the absence of extracellular Ca2+, indicating the major involvement of Ca2+ released from internal stores. Depolarization failed to induce intracellular calcium increases, although it disturbed the oscillation frequency, suggesting a putative modulator role of depolarizing agonists on the calcium oscillating pattern through voltage-gated calcium channels. Carbachol, a cholinergic agonist, evoked a switch in Ca2+ signaling from a calcium oscillating mode to a sustained and increased intracellular Ca2+ mode in 30% of measured cells, suggesting the involvement of acetylcholine in SCO activity, via a calcium-mediated response.

On-line analysis of gap junctions reveals more efficient electrical than dye coupling between islet cells

Pancreatic beta-cells constitute a well-communicating multicellular network that permits a coordinated and synchronized signal transmission within the islet of Langerhans that is necessary for proper insulin release. Gap junctions are the molecular keys that mediate functional cellular connections, which are responsible for electrical and metabolic coupling in the majority of cell types. Although the role of gap junctions in beta-cell electrical coupling is well documented, metabolic communication is still a matter of discussion. Here, we have addressed this issue by use of a fluorescence recovery after photobleaching (FRAP) approach. This technique has been validated as a reliable and noninvasive approach to monitor functional gap junctions in real time. We show that control pancreatic islet cells did not exchange a gap junction-permeant molecule in either clustered cells or intact islets of Langerhans under conditions that allowed cell-to-cell exchange of current-carrying ions. Conversely, we have detected that the same probe was extensively transferred between islet cells of transgenic mice expressing connexin 32 (Cx32) that have enhanced junctional coupling properties. The results indicate that the electrical coupling of native islet cells is more extensive than dye communication. Dye-coupling domains in islet cells appear more restricted than previously inferred with other methods.

Low doses of the endocrine disruptor bisphenol-A and the native hormone 17beta-estradiol rapidly activate transcription factor CREB

Endocrine-disrupting chemicals (EDCs) are hormone-like agents present in the environment that alter the endocrine system of wildlife and humans. Most EDCs have potencies far below those of the natural hormone 17beta-E2 when acting through the classic estrogen receptors (ERs). Here, we show that the environmental estrogen Bisphenol-A and the native hormone 17beta-E2 activate the transcription factor, cAMP-responsive element binding protein (CREB) with the same potency. Phosphorylated CREB (P-CREB) was increased after only a 5-minute application of either BPA or 17beta-E2 in a calcium-dependent manner. The effect was reproduced by the membrane-impermeable molecule E2 conjugated to horseradish peroxidase (E-HRP). The increase in P-CREB was not modified by the anti-estrogen ICI 182,780. Therefore, low-dose of BPA activates the transcription factor CREB via an alternative mechanism, involving a non-classical membrane estrogen receptor. Because these effects are elicited at concentrations as low as 10(-9) M, this observation is of environmental and public health relevance.

Nuclear KATP channels trigger nuclear Ca(2+) transients that modulate nuclear function

Glucose, the principal regulator of endocrine pancreas, has several effects on pancreatic beta cells, including the regulation of insulin release, cell proliferation, apoptosis, differentiation, and gene expression. Although the sequence of events linking glycemia with insulin release is well described, the mechanism whereby glucose regulates nuclear function is still largely unknown. Here, we have shown that an ATP-sensitive K(+) channel (K(ATP)) with similar properties to that found on the plasma membrane is also present on the nuclear envelope of pancreatic beta cells. In isolated nuclei, blockade of the K(ATP) channel with tolbutamide or diadenosine polyphosphates triggers nuclear Ca(2+) transients and induces phosphorylation of the transcription factor cAMP response element binding protein. In whole cells, fluorescence in situ hybridization revealed that these Ca(2+) signals may trigger c-myc expression. These results demonstrate a functional K(ATP) channel in nuclei linking glucose metabolism, nuclear Ca(2+) signals, and nuclear function.