Molecular Transduction Mechanisms Research Articles

Nicotinic agonists promoted the activation of nicotinic acetylcholine α7 receptors (α7 nAChR) in neurons, but failed to activate these receptors in mouse peritoneal macrophages

Nicotinic acetylcholine receptor (nAChR) of subtypes said "neuronal" are expressed in epithelial and immune system cells and participate in acetylcholine signaling by neural or non-neural pathways. It has been shown in macrophages that activation of type a7 nAChRs inhibits the release of pro-inflammatory cytokines, but the ion channel function has not been recorded in these cells. The objective of this work was to clarify what are the molecular mechanisms of transduction of a7 nAChRs in macrophages. To this end, RAW 264.7 cells, mouse peritoneal macrophages and rat hippocampal neurons were used. Cells were submitted to electrophysiological studies and stimulated with brief applications of the agonists acetylcholine, choline and nicotine, associated or not with the allosteric modulator PNU-120596. Responses to ATP were recorded as a reference. Furthermore, macrophages were submitted to cytokine quantitation. The electrophysiological results showed that macrophages responded to ATP but did not show whole-cell current by stimulation with nicotinic agonists. However, hippocampal neurons stimulated in the same pharmacological conditions of the macrophages showed ionic currents typical of the a7 nicotinic receptors. No effect of nicotine was observed in the lipopolysaccharide-induced TNF-a release. These results suggest that the a7 nAChR in macrophages do not work as ion channels similar to those expressed in neurons.

Electrophysiological characterisation of atrial volume receptors using ex vivo models of isolated rat cardiac atria.

What is the central question of this study? What ex vivo preparation of the rat's cavoatrial junction is efficient for characterising atrial mechanoreceptors? What is the main finding and its importance? Of four different ex vivo preparations, static pressure, flow, open and euthermic, the optimal preparation was the euthermic one and involved direct recording from the right cardiac vagal branch with a Langendorff style perfusion at 37°C. Type A receptors were most common, and appeared insensitive to stretch and sensitive to atrial contraction. Type B and intermediate receptors were not isolated at 20°C but were observed closer to 37°C. The findings may suggest that type A and B receptors utilise different molecular transduction mechanisms. Atrial volume receptors are a family of afferent neurons whose mechanically sensitive endings terminate in the atria, particularly at the cavoatrial junctions. These mechanosensors form the afferent limb of an atrial volume receptor reflex that regulates plasma volume. The prevailing functional classification of atrial receptors arose as a result of in vivo recordings in the cat and dog and were classified as type A, B or intermediate according to the timing of peak discharge during the cardiac cycle. In contrast, there have been far fewer studies of the common small laboratory mammals such as the rat. Using several ex vivo rat cavoatrial preparations, a total of 30 successful single cavoatrial mechanosensory recordings were obtained. These experiments show that the rat possesses type A, B and intermediate atrial mechanoreceptors as described for larger mammals. Recording these cavoatrial receptors proved challenging from the main vagus, but direct recording from the cardiac vagal branch greatly increased the yield of mechanically sensitive single units. In contrast to type A units, type B atrial mechanoreceptor activity was never observed at room temperature but required elevation of temperature to a more physiological range in order to be detected. The adequate stimulus for these receptors remains unclear; however, type A atrial receptors appear insensitive to direct atrial stretch when applied using a programmable positioner. The findings may suggest that type A and type B atrial receptors utilise different molecular transduction mechanisms.

Rotations of macromolecules affect nonspecific biological responses to magnetic fields

We have previously proposed that there are at least two initial molecular transduction mechanisms needed to explain specific and nonspecific biological effects of weak magnetic fields. For the specific effect associated with animal magnetic navigation, the radical pair mechanism is the leading hypothesis; it associates the specialised magnetic sense with the radical pairs located in the eye retina. In contrast to the magnetic sense, nonspecific effects occur through the interaction of magnetic fields with magnetic moments dispersed over the organism. However, it is unlikely that the radical pair mechanism can explain such nonspecific phenomena. In order to explain these, we further develop our physical model for the case of magnetic moments residing in rotating molecules. It is shown that, in some conditions, the precession of the magnetic moments that reside on rotating molecules can be slowed relative to the immediate biophysical structures. In terms of quantum mechanics this corresponds to the mixing of the quantum levels of magnetic moments. Hence this mechanism is called the Level Mixing Mechanism, or the LMM. The results obtained are magnetic field-dependences that are in good agreement with known experiments where biological effects arise in response to the reversal of the magnetic field vector.

Bcl-2 or Bcl-xL Overexpresssion Affects Both Lactic Fermentation and Mitochondrial Metabolism in Growing Pro-Lymphocytes

It is now well established that shifts in energy metabolism are associated with cancer development and progression. The most studied of these phenomena is the Warburg effect, which corresponds to an increase of anaerobic glycolysis vs mitochondrial oxidative phosphorylation to produce energy for cellular processes. However, the mechanisms related to these metabolic switches are still a matter of debate. Bcl-2 family proteins contain both pro- (e.g. Bax), and anti-apoptotic (e.g. Bcl-2 and Bcl-xL) members which are respectively encoded by tumor suppressors and proto-oncogenes. Up-regulation of the anti-apoptotic proteins Bcl-2 and Bcl-xL have been associated with Non-Hodgkin's lymphoma; and certain studies indicate that Bcl-2 family proteins play a role in the regulation of energy metabolism. However, the metabolic phenotypes associated directly with an overexpression of Bcl-2 or Bcl-xL (Bcl-2/xL) remain to be defined at the whole cell level. We recently applied a 1H- and 13C-NMR-based approach on growing Bcl-2/xL-overexpressing pro-lymphocyte B cell lines to determine their respective metabolic trends. The comparison of 1H-NMR spectra obtained from whole cell metabolites extractions indicate that significant metabolic changes are induced by Bcl-2/xL-overexpression; more particularly at the level of the intracellular fumarate pool. Also, both lactate production and glucose consumption fluxes are stimulated by Bcl-2/xL overexpression. This phenomenon is associated with an increase of glycolytic/fermentative (LDH and GAPDH enzyme activity) and mitochondrial (Citrate synthase activity) markers; but only when Bcl-xL (and not Bcl-2) is overexpressed. These data suggest that Bcl-2 and Bcl-xL expression levels may play an active role in the stimulation of lactic fermentation commonly observed in blood cancer cells; and that Bcl-2 and Bcl-xL-mediated stimulation of lactate production are the results of different molecular transduction mechanisms.

Photosensitization in Porphyrias and Photodynamic Therapy Involves TRPA1 and TRPV1

Photosensitization, an exaggerated sensitivity to harmless light, occurs genetically in rare diseases, such as porphyrias, and in photodynamic therapy where short-term toxicity is intended. A common feature is the experience of pain from bright light. In human subjects, skin exposure to 405 nm light induced moderate pain, which was intensified by pretreatment with aminolevulinic acid. In heterologous expression systems and cultured sensory neurons, exposure to blue light activated TRPA1 and, to a lesser extent, TRPV1 channels in the absence of additional photosensitization. Pretreatment with aminolevulinic acid or with protoporphyrin IX dramatically increased the light sensitivity of both TRPA1 and TRPV1 via generation of reactive oxygen species. Artificial lipid bilayers equipped with purified human TRPA1 showed substantial single-channel activity only in the presence of protoporphyrin IX and blue light. Photosensitivity and photosensitization could be demonstrated in freshly isolated mouse tissues and led to TRP channel-dependent release of proinflammatory neuropeptides upon illumination. With antagonists in clinical development, these findings may help to alleviate pain during photodynamic therapy and also allow for disease modification in porphyria patients. Cutaneous porphyria patients suffer from burning pain upon exposure to sunlight and other patients undergoing photodynamic therapy experience similar pain, which can limit the therapeutic efforts. This study elucidates the underlying molecular transduction mechanism and identifies potential targets of therapy. Ultraviolet and blue light generates singlet oxygen, which oxidizes and activates the ion channels TRPA1 and TRPV1. The disease and the therapeutic options could be reproduced in models ranging from isolated ion channels to human subjects, applying protoporphyrin IX or its precursor aminolevulinic acid. There is an unmet medical need, and our results suggest a therapeutic use of the pertinent antagonists in clinical development.

Somatostatin receptors and signaling cascades coupled to them

The peptide hormone somatostatin controlling function of CNS and peripheral organs and tissues realizes its regulatory effects via five types of somatostatin receptors (SomR) coupled to heterotrimeric G-proteins. Targets of the hormone action are the enzymes generating second messengers (adenylyl cyclase, phospholipase C, phosphatidylinositol-3-kinase), phosphotyrosine phosphatases, ion channels. The review summarizes and analyzes literature data and results of our investigations dealing with molecular mechanisms of transduction of the somatostatin signal into the cell, selectivity of interaction of SomR with heterotrimeric G-proteins and intracellular effectors as well as of effect of the SomR oligomerization on their functional activity.

International Conference on Purinergic Drugs and Targets—4th Joint German–Italian Purine Club Meeting, Bonn, Germany, July 22–25, 2011

International Conference on Purinergic Drugs and Targets—4th Joint German–Italian Purine Club Meeting, Bonn, Germany, July 22–25, 2011

Molecular receptors of taste agents

All representatives of higher eukaryotes can probably differentially perceive nutrients and poisonous substances. Molecular mechanisms of transduction of taste information have been best studied for mammals and for the fruit fly Drosophila. Here, we consider receptor mechanisms and conjugated primary signal processes of stimulation of taste receptor cells by stimuli of various taste modalities.

Molecular Transduction Mechanisms of the Redox Network Underlying the Antiproliferative Effects of Allyl Compounds from Garlic

Much evidence in the last few years suggests that the antiproliferative effects of various garlic secondary metabolites in in vitro experimental systems are due to redox-based mechanisms. In particular, sulfur-containing allyl compounds have been demonstrated to generate reactive oxygen species and to modify directly the redox state of specific reactive cysteines on protein surfaces. On the basis of such properties, allyl compounds, in particular the ones present in the oil-soluble fraction of garlic extracts, can function as modulators of several redox-mediated signaling pathways related to the activation of mitogen-activated protein kinases, cell cycle, DNA repair, and cell demise. However, even though many in vitro studies have tried to dissect the mechanisms of action of garlic derivatives, research in this field is still incomplete and questions about bioavailability, biotransformation, and pro-oxidant activity are still unanswered. This review discusses recent findings on such aspects, focusing on the chemistry of allyl compounds and their preferential cellular targets as well as on related nutritional aspects.

Molecular transduction mechanisms of cytokine–hormone interactions: role of gp130 cytokines

Highly sophisticated mechanisms confer on the immune system the capacity to respond with a certain degree of autonomy. However, the final outcome of an immune response depends on the interaction of the immune system with other systems. The immune and neuroendocrine systems have an intimate cross‐communication that makes possible a satisfactory response to environmental changes. Part of this interaction occurs through cytokines and steroid hormones. The last step of this cross‐talk is the molecular level. As a model of interaction, this review focuses on the gp130 cytokine family. These cytokines, as well as their receptors, are expressed in pituitary cells. They regulate hormone production as well as growth of pituitary cells. During acute or chronic inflammation or infection, systemic, hypothalamic and hypophyseal gp130 cytokines act on anterior pituitary cells, integrating the neuroendocrine–immune response. Disruptions of these pathways may lead not only to abnormal growth of pituitary cells but also to immune disorders, for which, based on recent findings, targeting these cytokines might be a novel therapeutic approach.

Molecular transduction mechanisms of cytokine hormone interactions: role of gp130 cytokines

Highly sophisticated mechanisms confer on the immune system the capacity to respond with a certain degree of autonomy. However, the final outcome of an immune response depends on the interaction of the immune system with other systems. The immune and neuroendocrine systems have an intimate cross-communication that makes possible a satisfactory response to environmental changes. Part of this interaction occurs through cytokines and steroid hormones. The last step of this cross-talk is the molecular level. As a model of interaction, this review focuses on the gp130 cytokine family. These cytokines, as well as their receptors, are expressed in pituitary cells. They regulate hormone production as well as growth of pituitary cells. During acute or chronic inflammation or infection, systemic, hypothalamic and hypophyseal gp130 cytokines act on anterior pituitary cells, integrating the neuroendocrine-immune response. Disruptions of these pathways may lead not only to abnormal growth of pituitary cells but also to immune disorders, for which, based on recent findings, targeting these cytokines might be a novel therapeutic approach.

Protein kinase C mediates neurotensin inhibition of inwardly rectifying potassium currents in rat substantia nigra dopaminergic neurons

Whole-cell voltage-clamp recordings were used to investigate the molecular transduction mechanism by which neurotensin decreases the inwardly rectifying potassium conductance of dopaminergic (DA) neurons acutely isolated from the rat substantia nigra (SN). With sodium-free external solution, neurotensin evoked inward currents by reducing the inwardly rectifying K + conductance. Neurotensin inhibition of the K + current was blocked by the internal perfusion of 1 mM GDP-β-S. When DA neurons were internally perfused with 0.5 mM GTP-γ-S, the reduction of K + conductance produced by neurotensin became irreversible. Neurotensin still inhibited K + currents in DA neurons pretreated with 500 ng/ml pertussis toxin (PTX). Dialyzing DA neurons with protein kinase C (PKC) inhibitors, staurosporine and PKC(19–31), prevented neurotensin from decreasing the potassium conductance. Our results propose that neurotensin activates PKC of SN DA neurons via PTX-insensitive G-proteins and that PKC mediates the neurotensin inhibition of inwardly rectifying potassium currents.

Olfaction and gustation in fish: an overview

Living in an aquatic environment, often devoid of light but rich in dissolved compounds, fish have highly developed chemosensory and chemical signalling systems. The olfactory and gustatory systems comprise the major chemosensory pathways. Despite considerable variations in structural organization of the peripheral olfactory organ throughout fish species, ultrastructural organization of the olfactory sensory epithelium is extremely consistent. The olfactory receptor cell is a bipolar neurone which is directly exposed to the external environment and sends information to the brain by its own axon (cranial nerve I). Four major classes of chemicals have been identified as specific olfactory stimuli and their stimulatory effectiveness characterized: amino acids, sex steroids, bile acids/salts and prostaglandins. Olfactory signals such as those involved in reproduction and feeding may be processed independently through two distinct subsystems: the lateral and medial olfactory systems. The taste buds constitute the structural basis of the gustatory organ. Taste buds may occur not only in the oropharyngeal cavity, but on the whole body surface. Chemical information detected by specialized epithelial cells, gustatory cells, is transmitted to the central nervous system by cranial nerve VII (facial), IX (glossopharyngeal), and X (vagal). Besides diverse sensitivities and specificities for amino acids, fish gustatory receptors detect various organic acids, nucleotides and bile salts. Putative receptors, molecular mechanisms of transduction and the role played by olfaction and gustation in feeding, reproduction, migration and other fish behaviours are discussed.

Insulin and IGF-1 signaling in oocyte maturation.

Xenopus laevis oocytes possess insulin and/or insulin-like growth factor-1 (IGF-1) receptors and respond to respective hormones by increasing glucose transport and progressing from the G2 to M phase of the cell cycle (maturation). While molecular transduction mechanisms involving mitogen-activating kinases and cyclin-dependent kinases begin to be elucidated, missing links remain between the initial receptor tyrosine phosphorylation events and downstream signaling. The discovery that phosphotyrosines produced by receptor autophosphorylation or during substrate phosphorylation serve as an anchor for src homology 2 domains of several signaling proteins had a major impact on understanding how cytoplasmic enzymes are recruited at the level of the plasma membrane for subsequent activation.

生体膜における化学センサーをモデルとした人工膜センサー

In biological systems, most typical chemical sensors are olfactory and taste organs. The present article deals with molecular mechanisms of transduction in these organs and artificial chemical sensor based on the mechanisms in the organs.The responses to odorants are seen not only in olfactory systems but also in non-olfactory systems such as neuroblastoma cells which must have no specific receptor proteins for odorants. The lipid bilayers also exhibit the membrane potential changes in response to various odorants similarly to olfactory cells. Changes in lipid composition of the membranes lead to changes in specificity of the membranes to odorants. Odor discrimination can be explained by postulating that the membrane composition of each olfactory cell is different from cell to cell.Sweet substances and amino acids are recognized by specific receptor proteins in taste receptor membranes, while specific proteins unique to taste cells are not concerned with reception of salts, acids and bitter substances. The membrane potential of lipid bilayers is changed inresponse to various bitter substances similarly to taste cells. The membrane potential changes are induced by the phase boundary potential changes.

Molecular transduction mechanisms in ACTH-induced grooming.

Intraventricular administration of ACTH1-24 induces excessive grooming in the rat. Ethogram analysis shows that the peptide does not alter grooming behavior seen in a novel box, but that it prolongs the duration of the grooming bout. Extensive structure-activity studies have been performed which suggest that the active site lies in a region (5-13) of the ACTH molecule. Interestingly, the (1-24) sequence is fully active, whereas (1-10) and (11-24) alone or in combination are inactive, pointing to a specific stereoconformation necessary to induce grooming. However, despite the fact that there are ACTH-and/or alpha-MSH-containing peptidergic neurons, no conclusive evidence is available demonstrating stereospecific, saturable binding sites for these peptides in brain. The analysis of the neural substrate underlying ACTH-induced excessive grooming has been performed by means of electrolytic lesions of specific brain regions and by neuropharmacological manipulations. The data suggest that the periaqueductal gray is the primary target for ACTH and that the activity of neostriatum and accumbens, via a nigro-colliculus-periaqueductal gray pathway, modulates the display of excessive grooming. An important feature of the neural substrate is that it displays single-dose tolerance to the peptide during the first hours after the first peptide injection. It is suggested that the tolerance is a feature of an opioid receptor-containing component of the neural substrate. The molecular mechanism of action of ACTH is complex and may involve different transmembrane signal transduction systems. The peptide decreases the degree of phosphorylation of a neuron-specific, synaptic phosphoprotein B-50 by inhibition of protein kinase C. It is concluded that changes in the degree of phosphorylation of B-50 regulate the activity of the lipid kinase phosphatidylinositol 4-phosphate kinase. Therefore, the B-50 protein seems to be part of a negative feedback loop in the receptor-activated hydrolysis of phosphatidylinositol 4,5-bis-phosphate (PIP2). There is increasing evidence that the molecular mechanism by which ACTH brings about the grooming response involves a change in phosphorylation of B-50. Firstly, the structure-activity relationship of ACTH-induced excessive grooming is nearly identical to that obtained for ACTH-induced inhibition of protein kinase C.(ABSTRACT TRUNCATED AT 400 WORDS)