Biomedical subjects

Angel Nadal

Publications and source records attributed to Angel Nadal.

6 recordsLinked to original sources

PubMed2003

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.

Analgesics, Non-Narcotic↗

PubMed2003

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.

Animals↗

PubMed2003

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.

Acetylcholine↗

PubMed2002

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.

Animals↗

PubMed2002

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.

Adenosine Triphosphate↗

PubMed2002

A nonclassical estrogen membrane receptor triggers rapid differential actions in the endocrine pancreas.

Glucose homeostasis in blood is mainly maintained by insulin released from beta-cells and glucagon released from alpha-cells, both integrated within the pancreatic islet of Langerhans. The secretory processes in both types of cells are triggered by a rise in intracellular calcium concentration ([Ca2+](i)). In this study, rapid effects of the natural hormone E2 on [Ca2+](i) were studied in both types of cells within intact islets using laser scanning confocal microscopy. alpha- And beta-cells showed opposite [Ca2+](i) responses when stimulated with physiological concentrations of 17beta-E2. Although the estrogen produced an increase in the frequency of glucose-induced [Ca2+](i) oscillations in insulin-releasing beta-cells, it prevented the low glucose-induced [Ca2+](i) oscillations in glucagon-releasing alpha-cells. The effects of 17beta-E2 on alpha-cells were mimicked by the cGMP permeable analog 8bromo-cGMP and blocked by the cGMP-dependent protein kinase (PKG) inhibitor KT5823. Evidence indicated that these were membrane actions mediated by a nonclassical ER. Both effects were rapid in onset and were reproduced by 17beta-E2 linked to horseradish peroxidase, a cell-impermeable molecule. Furthermore, these actions were not blocked by the specific ER blocker ICI 182,780. Competition studies performed with 17beta-E2 linked to horseradish peroxidase binding in alpha-cells supported the idea that the membrane receptor involved is neither ERalpha nor ERbeta. Additionally, the binding site was shared by the neurotransmitters epinephrine, norepinephrine, and dopamine and had the same pharmacological profile as the receptor previously described for beta-cells. Therefore, rapid estrogen actions in islet cells are initiated by a nonclassical estrogen membrane receptor.

Alkaloids↗