Secretion of Interleukin 6 in Human Skeletal Muscle Cultures Depends on Ca2+ Signalling

The systemic effects of physical activity are mediated by the release of IL-6 and other myokines from contracting muscle. Although the release of IL-6 from muscle has been extensively studied, the information on the cellular mechanisms is fragmentary and scarce, especially regarding the role of Ca²⁺ signals. The aim of this study was to characterize the role of the main components of Ca²⁺ signals in human skeletal muscle cells during IL-6 secretion stimulated by the Ca²⁺ mobilizing agonist ATP. Primary cultures were prepared from surgical samples, fluorescence microscopy was used to evaluate the Ca²⁺ signals and the stimulated release of IL-6 into the medium was determined using ELISA. Intracellular calcium chelator Bapta, low extracellular calcium and the Ca²⁺ channels blocker La³⁺ reduced the ATP-stimulated, but not the basal secretion. Secretion was inhibited by blockers of L-type (nifedipine, verapamil), T-type (NNC55-0396) and Orai1 (Synta66) Ca²⁺ channels and by silencing Orai1 expression. The same effect was achieved with inhibitors of ryanodine receptors (ryanodine, dantrolene) and IP3 receptors (xestospongin C, 2-APB, caffeine). Inhibitors of calmodulin (calmidazolium) and calcineurin (FK506) also decreased secretion. IL-6 transcription in response to ATP was not affected by Bapta or by the T channel blocker. Our results prove that ATP-stimulated IL-6 secretion is mediated at the post-transcriptional level by Ca²⁺ signals, including the mobilization of calcium stores, the activation of store-operated Ca²⁺ entry, and the subsequent activation of voltage-operated Ca²⁺ channels and calmodulin/calcineurin pathways.

Flavonoids promote Rhizophagus irregularis spore germination and tomato root colonization: A target for sustainable agriculture

The use of arbuscular mycorrhizal (AM) fungi has great potential, being used as biostimulants, biofertilizers and bioprotection agents in agricultural and natural ecosystems. However, the application of AM fungal inoculants is still challenging due to the variability of results when applied in production systems. This variability is partly due to differences in symbiosis establishment. Reducing such variability and promoting symbiosis establishment is essential to improve the efficiency of the inoculants. In addition to strigolactones, flavonoids have been proposed to participate in the pre-symbiotic plant-AM fungus communication in the rhizosphere, although their role is still unclear. Here, we studied the specific function of flavonoids as signaling molecules in AM symbiosis. For that, both in vitro and in planta approaches were used to test the stimulatory effect of an array of different subclasses of flavonoids on Rhizophagus irregularis spore germination and symbiosis establishment, using physiological doses of the compounds. We show that the flavone chrysin and the flavonols quercetin and rutin were able to promote spore germination and root colonization at low doses, confirming their role as pre-symbiotic signaling molecules in AM symbiosis. The results pave the way to use these flavonoids in the formulation of AM fungal-based products to promote the symbiosis. This can improve the efficiency of commercial inoculants, and therefore, help to implement their use in sustainable agriculture.

Untapping the potential of plant mycobiomes for applications in agriculture

Plant-fungal interactions are widespread in nature, and their multiple benefits for plant growth and health have been amply demonstrated. Endophytic and epiphytic fungi can significantly increase plant resilience, improving plant nutrition, stress tolerance and defence. Although some of these interactions have been known for decades, the relevance of the plant mycobiome within the plant microbiome has been largely underestimated. Our limited knowledge of fungal biology and their interactions with plants in the broader phytobiome context has hampered the development of optimal biotechnological applications in agrosystems and natural ecosystems. Exciting recent technical and knowledge advances in the context of molecular and systems biology open a plethora of opportunities for developing this field of research.

Roots drive oligogalacturonide-induced systemic immunity in tomato

Oligogalacturonides (OGs) are fragments of pectin released from the plant cell wall during insect or pathogen attack. They can be perceived by the plant as damage signals, triggering local and systemic defence responses. Here, we analyse the dynamics of local and systemic responses to OG perception in tomato roots or shoots, exploring their impact across the plant and their relevance in pathogen resistance. Targeted and untargeted metabolomics and gene expression analysis in plants treated with purified OGs revealed that local responses were transient, while distal responses were stronger and more sustained. Remarkably, changes were more conspicuous in roots, even upon foliar application of the OGs. The treatments differentially activated the synthesis of defence-related hormones and secondary metabolites including flavonoids, alkaloids and lignans, some of them exclusively synthetized in roots. Finally, the biological relevance of the systemic defence responses activated upon OG perception was confirmed, as the treatment induced systemic resistance to Botrytis cinerea. Overall, this study shows the differential regulation of tomato defences upon OGs perception in roots and shoots and reveals the key role of roots in the coordination of the plant responses to damage sensing.

Ménage à Trois: Unraveling the Mechanisms Regulating Plant-Microbe-Arthropod Interactions

Plant-microbe-arthropod (PMA) three-way interactions have important implications for plant health. However, our poor understanding of the underlying regulatory mechanisms hampers their biotechnological applications. To this end, we searched for potential common patterns in plant responses regarding taxonomic groups or lifestyles. We found that most signaling modules regulating two-way interactions also operate in three-way interactions. Furthermore, the relative contribution of signaling modules to the final plant response cannot be directly inferred from two-way interactions. Moreover, our analyses show that three-way interactions often result in the activation of additional pathways, as well as in changes in the speed or intensity of defense activation. Thus, detailed, basic knowledge of plant-microbe-arthropod regulation will be essential for the design of environmentally friendly crop management strategies.

Age-Induced Differential Changes in the Central and Colonic Human Circadian Oscillators

Aging modifies not only multiple cellular and homeostatic systems, but also biological rhythms. The circadian system is driven by a central hypothalamic oscillator which entrains peripheral oscillators, in both cases underlain by circadian genes. Our aim was to characterize the effect of aging in the circadian expression of clock genes in the human colon. Ambulatory recordings of the circadian rhythms of skin wrist temperature, motor activity and the integrated variable TAP (temperature, activity and position) were dampened by aging, especially beyond 74 years of age. On the contrary, quantitative analysis of genes expression in the muscle layer of colonic explants during 24 h revealed that the circadian expression of Bmal1, Per1 and Clock genes, was larger beyond that age. In vitro experiments showed that aging induced a parallel increase in the myogenic contractility of the circular colonic muscle. This effect was not accompanied by enhancement of Ca²⁺ signals. In conclusion, we describe here for the first time the presence of a molecular oscillator in the human colon. Aging has a differential effect on the systemic circadian rhythms, that are impaired by aging, and the colonic oscillator, that is strengthened in parallel with the myogenic contractility.

Molecular dialogue between arbuscular mycorrhizal fungi and the nonhost plant Arabidopsis thaliana switches from initial detection to antagonism

Approximately 29% of all vascular plant species are unable to establish an arbuscular mycorrhizal (AM) symbiosis. Despite this, AM fungi (Rhizophagus spp.) are enriched in the root microbiome of the nonhost Arabidopsis thaliana, and Arabidopsis roots become colonized when AM networks nurtured by host plants are available. Here, we investigated the nonhost-AM fungus interaction by analyzing transcriptional changes in Rhizophagus, Arabidopsis and the host plant Medicago truncatula while growing in the same mycorrhizal network. In early interaction stages, Rhizophagus activated the Arabidopsis strigolactone biosynthesis genes CCD7 and CCD8, suggesting that detection of AM fungi is not completely impaired. However, in colonized Arabidopsis roots, fungal nutrient transporter genes GintPT, GintAMT2, GintMST2 and GintMST4, essential for AM symbiosis, were not activated. RNA-seq transcriptome analysis pointed to activation of costly defenses in colonized Arabidopsis roots. Moreover, Rhizophagus colonization caused a 50% reduction in shoot biomass, but also led to enhanced systemic immunity against Botrytis cinerea. This suggests that early signaling between AM fungi and Arabidopsis is not completely impaired and that incompatibility appears at later interaction stages. Moreover, Rhizophagus-mediated defenses coincide with reduced Arabidopsis growth, but also with systemic disease resistance, highlighting the multifunctional role of AM fungi in host and nonhost interactions.

Growing Research Networks on Mycorrhizae for Mutual Benefits

Research on mycorrhizal interactions has traditionally developed into separate disciplines addressing different organizational levels. This separation has led to an incomplete understanding of mycorrhizal functioning. Integration of mycorrhiza research at different scales is needed to understand the mechanisms underlying the context dependency of mycorrhizal associations, and to use mycorrhizae for solving environmental issues. Here, we provide a road map for the integration of mycorrhiza research into a unique framework that spans genes to ecosystems. Using two key topics, we identify parallels in mycorrhiza research at different organizational levels. Based on two current projects, we show how scientific integration creates synergies, and discuss future directions. Only by overcoming disciplinary boundaries, we will achieve a more comprehensive understanding of the functioning of mycorrhizal associations.

Mycorrhizal tomato plants fine tunes the growth-defence balance upon N depleted root environments

In low nutritive environments, the uptake of N by arbuscular mycorrhizal (AM) fungi may confer competitive advantages for the host. The present study aims to understand how mycorrhizal tomato plants perceive and then prepare for an N depletion in the root environment. Plants colonized by Rhizophagus irregularis displayed improved responses to a lack of N than nonmycorrhizal (NM) plants. These responses were accomplished by a complex metabolic and transcriptional rearrangement that mostly affected the gibberellic acid and jasmonic acid pathways involving DELLA and JAZ1 genes, which were responsive to changes in the C/N imbalance of the plant. N starved mycorrhizal plants showed lower C/N equilibrium in the shoots than starved NM plants and concomitantly a downregulation of the JAZ1 repressor and the increased expression of the DELLA gene, which translated into a more active oxylipin pathway in mycorrhizal plants. In addition, the results support a priorization in AM plants of stress responses over growth. Therefore, these plants were better prepared for an expected stress. Furthermore, most metabolites that were severely reduced in NM plants following the N depletion remained unaltered in starved AM plants compared with those normally fertilized, suggesting that the symbiosis buffered the stress, improving plant development in a stressed environment.

The Nitrogen Availability Interferes with Mycorrhiza-Induced Resistance against Botrytis cinerea in Tomato

Mycorrhizal plants are generally quite efficient in coping with environmental challenges. It has been shown that the symbiosis with arbuscular mycorrhizal fungi (AMF) can confer resistance against root and foliar pathogens, although the molecular mechanisms underlying such mycorrhiza-induced resistance (MIR) are poorly understood. Tomato plants colonized with the AMF Rhizophagus irregularis display enhanced resistance against the necrotrophic foliar pathogen Botrytis cinerea. Leaves from arbuscular mycorrhizal (AM) plants develop smaller necrotic lesions, mirrored also by a reduced levels of fungal biomass. A plethora of metabolic changes takes place in AMF colonized plants upon infection. Certain changes located in the oxylipin pathway indicate that several intermediaries are over-accumulated in the AM upon infection. AM plants react by accumulating higher levels of the vitamins folic acid and riboflavin, indolic derivatives and phenolic compounds such as ferulic acid and chlorogenic acid. Transcriptional analysis support the key role played by the LOX pathway in the shoots associated with MIR against B. cinerea. Interestingly, plants that have suffered a short period of nitrogen starvation appear to react by reprogramming their metabolic and genetic responses by prioritizing abiotic stress tolerance. Consequently, plants subjected to a transient nitrogen depletion become more susceptible to B. cinerea. Under these experimental conditions, MIR is severely affected although still functional. Many metabolic and transcriptional responses which are accumulated or activated by MIR such NRT2 transcript induction and OPDA and most Trp and indolic derivatives accumulation during MIR were repressed or reduced when tomato plants were depleted of N for 48 h prior infection. These results highlight the beneficial roles of AMF in crop protection by promoting induced resistance not only under optimal nutritional conditions but also buffering the susceptibility triggered by transient N depletion.

Recognizing Plant Defense Priming

Defense priming conditions diverse plant species for the superinduction of defense, often resulting in enhanced pest and disease resistance and abiotic stress tolerance. Here, we propose a guideline that might assist the plant research community in a consistent assessment of defense priming in plants.

Propagation of Intracellular Ca2+ Signals in Aged Exocrine Cells

There is little information on the effects of aging in the propagation of calcium signals and its underlying mechanisms. We studied the effects of aging on propagation of Ca(2+) signals in pancreatic acinar cells. Fura-2 loaded cells isolated from young (3-4 months old) and aged (24 months old) mouse responded to acetylcholine (ACh) and cholecystokinin (CCK) with a polarized Ca(2+) response initiated at the secretory pole before spreading to the basal one. Aging slowed down the propagation of the response to ACh but enhanced the velocity of the CCK response. This pattern can be explained by the age-induced depolarization of mitochondria, because it can be reproduced in young cells by mitochondrial inhibitors. Aging also increased the role of acidic stores in the CCK signal, as judged by the folimycin-induced suppression of the polarization in aged but not in young cells. The involvement of ryanodine receptors in the ACh response was also enhanced, as indicated by the loss of polarization after the treatment with 8Br-cyclic ADP ribose. Therefore, we conclude that aging modifies differentially the propagation of ACh and CCK-evoked Ca(2+) signals through mitochondrial depolarization and changes in the role of the acidic Ca(2+) stores and ryanodine receptors in the initiation of the signals.

Defense related phytohormones regulation in arbuscular mycorrhizal symbioses depends on the partner genotypes

Arbuscular mycorrhizal (AM) symbioses are mutualistic associations between soil fungi and most vascular plants. Modulation of the hormonal and transcriptional profiles, including changes related to defense signalling, has been reported in many host plants during AM symbioses. These changes have been often related to the improved stress tolerance common in mycorrhizal plants. However, results on the alterations in phytohormones content and their role on the symbiosis are controversial. Here, an integrative analysis of the response of phylogenetically diverse plants (i.e., tomato, soybean, and maize) to two mycorrhizal fungi -Funneliformis mosseae and Rhizophagus irregularis- was performed. The analysis of the defense-related hormones salicylic acid, abscisic acid, and jasmonates, and the expression of marker genes of the pathways they regulate, revealed significant changes in the roots of mycorrhizal plants. These changes depended on both the plant and the AM fungus (AMF) involved. However, general trends can be identified: roots associated with the most effective colonizer R. irregularis showed fewer changes in these defense-related traits, while the colonization by F. mosseae led to significant modifications in all plants tested. The up-regulation of the jasmonate pathway by F. mosseae was found to be highly conserved among the different plant species, suggesting an important role of jasmonates during this AM interaction. Our study evidences a strong influence of the AMF genotype on the modulation of host defense signalling, and offers hints on the role of these changes in the symbiosis.

Age-related changes in mitochondrial function of mouse colonic smooth muscle: beneficial effects of melatonin

Aging is a multifactorial process that involves biochemical, structural, and functional changes in mitochondria. The ability of melatonin to palliate the alterations induced by aging is based on its chronobiologic, antioxidant, and mitochondrial effects. There is little information about the effects of melatonin on the in situ mitochondrial network of aging cells and its physiological implications. We have studied the ability of melatonin to prevent the functional alterations of in situ mitochondria of smooth muscle cells and its impact on contractility. Mitochondrial membrane potential was recorded in isolated colonic smooth muscle cells from young mice (3 month old), aged mice (22-24-month old), and aged mice treated with melatonin (starting at 14-month age). Aging induced a partial mitochondrial depolarization in resting conditions and reduced the depolarizing response to cellular stimulation. Use of oligomycin indicated that aging enhanced the resting activity of the mitochondrial ATP synthase, whereas in young cells, the enzyme operated mainly in reverse mode. Melatonin treatment prevented all these changes. Aging reduced both spontaneous and stimulated contraction of colonic strips and shifted the metabolic dependence of contraction from mitochondria to glycolysis, as indicated the use of mitochondrial and glycolysis inhibitors. These functional alterations were also palliated by melatonin treatment. Aging effects were not related to a decrease in Ca2+ store mobilization, because this was enhanced in aged cells and restored by melatonin. In conclusion, melatonin prevents the age induced in situ mitochondrial potential alterations in smooth muscle cells and the associated changes in contractility and metabolism.

mTOR pathway and Ca²⁺ stores mobilization in aged smooth muscle cells

Aging is considered to be driven by the so called senescence pathways, especially the mTOR route, although there is almost no information on its activity in aged tissues. Aging also induces Ca²⁺ signal alterations, but information regarding the mechanisms for these changes is almost inexistent. We investigated the possible involvement of the mTOR pathway in the age-dependent changes on Ca²⁺ stores mobilization in colonic smooth muscle cells of young (4 month old) and aged (24 month old) guinea pigs. mTORC1 activity was enhanced in aged smooth muscle, as revealed by phosphorylation of mTOR and its direct substrates S6K1 and 4E-BP1. Mobilization of intracellular Ca²⁺ stores through IP₃R or RyR channels was impaired in aged cells, and it was facilitated by mTOR and by FKBP12, as indicated by the inhibitory effects of KU0063794 (a direct mTOR inhibitor), rapamycin (a FKBP12-mediated mTOR inhibitor) and FK506 (an FKBP12 binding immunosuppressant). Aging suppressed the facilitation of the Ca²⁺ mobilization by FKBP12 but not by mTOR, without changing the total expression of FKBP12 protein. In conclusion, or study shows that in smooth muscle aging enhances the constitutive activity of mTORC1 pathway and impairs Ca²⁺ stores mobilization by suppression of the FKBP12-induced facilitation of Ca²⁺ release.

NFATc3 regulates trypsinogen activation, neutrophil recruitment, and tissue damage in acute pancreatitis in mice

BACKGROUND & AIMS

The signaling mechanisms that regulate trypsinogen activation and inflammation in acute pancreatitis (AP) are unclear. We explored the involvement of the calcium- and calcineurin-dependent transcription factor nuclear factor of activated T cells (NFAT) in development of AP in mice.

METHODS

We measured levels of myeloperoxidase and macrophage inflammatory protein 2 (CXCL2), trypsinogen activation, and tissue damage in the pancreas 24 hours after induction of AP by retrograde infusion of taurocholate into the pancreatic ducts of wild-type, NFAT luciferase reporter (NFAT-luc), and NFATc3-deficient mice. We isolated acinar cells and measured NFAT nuclear accumulation, trypsin activity, and expression of NFAT-regulated genes.

RESULTS

Infusion of taurocholate increased the transcriptional activity of NFAT in the pancreas, aorta, lung, and spleen of NFAT-luc mice. Inhibition of NFAT with A-285222 blocked taurocholate-induced activation of NFAT in all organs. A-285222 also reduced taurocholate-induced increases in levels of amylase, myeloperoxidase, and CXCL2; activation of trypsinogen; necrosis of acinar cells; edema; leukocyte infiltration; and hemorrhage in the pancreas. NFATc3-deficient mice were protected from these effects of taurocholate. Similar results were obtained using an l-arginine-induced model of AP. Reverse-transcription polymerase chain reaction and confocal immunofluorescence analyses showed that NFATc3 is expressed by acinar cells. NFATc3 expression was activated by stimuli that increase intracellular calcium levels, and activation was prevented by the calcineurin blocker cyclosporin A or A-285222. Activation of trypsinogen by secretagogues in acinar cells was prevented by pharmacologic inhibition of NFAT signaling or lack of NFATc3. A-285222 also reduced expression of inflammatory cytokines such as CXCL2 in acinar cells.

CONCLUSIONS

NFATc3 regulates trypsinogen activation, inflammation, and pancreatic tissue damage during development of AP in mice and might be a therapeutic target.

Aging impairs Ca2+ sensitization pathways in gallbladder smooth muscle

Calcium sensitization is an important physiological process in agonist-induced contraction of smooth muscle. In brief, calcium sensitization is a pathway that leads to smooth muscle contraction independently of changes in [Ca(2+)](i) by mean of inhibition of myosin light chain phosphatase. Aging has negative impacts on gallbladder contractile response due to partial impairment in calcium signaling and alterations in the contractile machinery. However, information regarding aging-induced alterations in calcium sensitization is scanty. We hypothesized that the calcium sensitization system is negatively affected by age. To investigate this, gallbladders were collected from adult (4 months old) and aged (22-24 months old) guinea pigs. To evaluate the contribution of calcium sensitization pathways we assayed the effect of the specific inhibitors Y-27632 and GF109203X on the "in vitro" isometric gallbladder contractions induced by agonist challenges. In addition, expression and phosphorylation (as activation index) of proteins participating in the calcium sensitization pathways were quantified by Western blotting. Aging reduced bethanechol- and cholecystokinin-evoked contractions, an effect associated with a reduction in MLC20 phosphorylation and in the effects of both Y-27632 and GF109203X. In addition, there was a drop in ROCK I, ROCK II, MYPT-1 and PKC expression and in the activation/phosphorylation of MYPT-1, PKC and CPI-17 in response to agonists. Interestingly, melatonin treatment for 4 weeks restored gallbladder contractile responses due to re-establishment of calcium sensitization pathways. These results demonstrate that age-related gallbladder hypocontractility is associated to alterations of calcium sensitization pathways and that melatonin treatment exerts beneficial effects in the recovery of gallbladder contractility.

Mycorrhiza-induced resistance and priming of plant defenses

Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas.

Mycorrhiza-induced resistance and priming of plant defenses

Symbioses between plants and beneficial soil microorganisms like arbuscular-mycorrhizal fungi (AMF) are known to promote plant growth and help plants to cope with biotic and abiotic stresses. Profound physiological changes take place in the host plant upon root colonization by AMF affecting the interactions with a wide range of organisms below- and above-ground. Protective effects of the symbiosis against pathogens, pests, and parasitic plants have been described for many plant species, including agriculturally important crop varieties. Besides mechanisms such as improved plant nutrition and competition, experimental evidence supports a major role of plant defenses in the observed protection. During mycorrhiza establishment, modulation of plant defense responses occurs thus achieving a functional symbiosis. As a consequence of this modulation, a mild, but effective activation of the plant immune responses seems to occur, not only locally but also systemically. This activation leads to a primed state of the plant that allows a more efficient activation of defense mechanisms in response to attack by potential enemies. Here, we give an overview of the impact on interactions between mycorrhizal plants and pathogens, herbivores, and parasitic plants, and we summarize the current knowledge of the underlying mechanisms. We focus on the priming of jasmonate-regulated plant defense mechanisms that play a central role in the induction of resistance by arbuscular mycorrhizas.

Immunoreactivity for Ano1 detects depletion of Kit-positive interstitial cells of Cajal in patients with slow transit constipation

BACKGROUND

Depletion of interstitial cells of Cajal (ICC) is associated with several gastrointestinal (GI) motility disorders. Changes in ICC networks are usually detected by immunolabeling for the receptor tyrosine kinase Kit. Ano1 (DOG1 or TMEM16A) was recently described as a marker of ICC in GI tract. Our aim was to determine whether Ano1 immunoreactivity can be used as a reliable marker for ICC in tissues from patients with motility disorders.

METHODS

Four tissues from patients with normal ICC numbers and four tissues from patients with slow transit constipation and loss of Kit-positive ICC were studied. Interstitial cells of Cajal were detected by double labeling using antisera to Kit and Ano1.

KEY RESULTS

Both the processes and cell bodies of ICC in tissue from controls and slow transit constipation were immunoreactive for Ano1. There was a near complete overlap between Kit and Ano1 immunoreactivity. Tissues from patients with slow transit constipation contained significantly fewer Ano1-positive ICC than control tissues. The numbers of ICC identified by Ano1 and Kit immunoreactivity were nearly identical across the range of ICC numbers from an average of 1.64 to 7.05 cells per field and correlated with an R(2) value of 0.99.

CONCLUSIONS & INFERENCES

Ano1 is a reliable and sensitive marker for detecting changes in ICC networks in humans. Labeling with antibodies selective for Ano1 reproducibly detects depletion of Kit-positive ICC in tissues from patients with slow transit constipation.

Melatonin, a potential therapeutic agent for smooth muscle-related pathological conditions and aging

Increases or decreases in the contractile response of smooth muscle underlie important pathological conditions such as hypertension, incontinence and altered gastrointestinal transit. These disorders are also frequently encountered in the aged population. Oxidative stress and inflammation are key features in the initiation, progression, and clinical manifestations of smooth muscle disorders. Melatonin, the major secretory product of the pineal gland, has free radical scavenging and antioxidative properties and protects against oxidative insult. Recently, widespread interest has grown regarding the apparent protective effects of melatonin on smooth muscle dysfunction. "In vitro" studies have shown that melatonin decreased vascular tone of vascular beds from control, hypertensive or aged animals, through the reduction of adrenergic contraction and the increase in acetylcholine-induced relaxation. "In vivo", melatonin also attenuates sympathetic tone by direct activation of melatonin receptors, scavenging free radicals or increasing NO availability in the central nervous system. In the gastrointestinal tract, melatonin treatment improves age-related impairments in gallbladder contractility and prevents deleterious effects of cholecystitis on smooth muscle and the enteric nervous system through suppression of oxidative stress. In addition, melatonin improves colonic transit time in constipation-predominant IBS patients. Melatonin is also able to restore impaired contractility of the detrusor muscle from old animals through normalization of Ca(2+) dependent and independent contraction, mitochondrial polarity, neuromuscular function and oxidative stress, which would explain the effects of melatonin counteracting cystometric changes in senescent animals. It also reverses bladder damage following ischemia/reperfusion. In conclusion, melatonin may be a promising candidate for future research of agents that modulate smooth muscle motility.

Aging differentially modifies agonist-evoked mouse detrusor contraction and calcium signals

Although aging-induced changes in urinary bladder neurotransmission have been studied in some detail, information regarding alterations in detrusor muscle is scanty and addresses only partial aspects of the myogenic response of detrusor. Rodent bladder aging shows several features similar to those reported in humans. The aim of this study was to characterize in aged mouse the alterations of detrusor muscle contraction and the putative underlying changes in Ca(2+) signals. We studied in vitro the myogenic contraction induced by agonists in detrusor strips from adult (3 months old) or aged (23-25 months old) mice. In addition, we determined the agonist-induced [Ca(2+)](i) signals by epifluorescence microscopy in fura-2 loaded isolated detrusor cells. Aging impaired the contractile response of bladder strips to cholinergic stimulation with bethanechol and to chemical depolarization with KCl-containing solutions. On the contrary, the response to purinergic stimulation (ATP) was enhanced. Aging also diminished the transient Ca(2+) signal evoked by bethanechol and the Ca(2+) influx induced by KCl in bladder strips. Treatments aimed to release calcium from intracellular stores (caffeine and a low level of ionomycin in Ca(2+)-free medium) showed that aging reduces the size of agonist-releasable stores. Similar to contraction, the mobilization of Ca(2+) by ATP was increased in aged cells. Therefore, the differential effects of aging on detrusor contraction are associated to alterations of [Ca(2+)](i) signals: the cholinergic inhibition is due to inhibition of voltage-operated Ca(2+) influx and reduction of the size of intracellular Ca(2+) stores, while the age-induced ATP response is accompanied by an enhanced Ca(2+) mobilization.

Arbuscular mycorrhizal symbiosis decreases strigolactone production in tomato

Strigolactones are a new class of plant hormones emerging as important signals in the control of plant architecture. In addition, they are key elements in plant communication with several rhizosphere organisms. Strigolactones are exuded into the soil, where they act as host detection signals for arbuscular mycorrhizal (AM) fungi, but also as germination stimulants for root parasitic plant seeds. Under phosphate limiting conditions, plants up-regulate the secretion of strigolactones into the rhizosphere to promote the formation of AM symbiosis. Using tomato as a model plant, we have recently shown that AM symbiosis induces changes in transcriptional and hormonal profiles. Using the same model system, here we analytically demonstrate, using liquid chromatography-tandem mass spectrometry, that strigolactone production is also significantly reduced upon AM symbiosis. Considering the dual role of the strigolactones in the rhizosphere as signals for AM fungi and parasitic plants, we discuss the potential implications of these changes in the plant interaction with both organisms.

Changes in interstitial cells of cajal with age in the human stomach and colon

BACKGROUND

Aging produces inevitable changes in the function of most organs including the gastrointestinal tract. Together with enteric nerves and smooth muscle cells, interstitial cells of Cajal (ICC) play a key role in the control of gastrointestinal motility, yet little is known about the effect of aging on ICC. The aim of this study was to determine the effect of aging on ICC number and volume in the human stomach and colon.

METHODS

Gastric and colonic tissues from patients aged 25-70 and 36-92 years old, respectively, and with no co-existent motility disorders were immunolabeled with an anti-Kit antibody and ICC were counted in the circular muscle and myenteric regions. Network volumes were measured using 3D reconstructions of confocal stacks. The effects of aging were determined by testing for linear trends using regression analysis.

KEY RESULTS

In both stomach and colon, the number of ICC bodies and volume significantly decreased with age at a rate of 13% per decade. ICC size was only affected in the myenteric plexus in the colon. The changes associated with age were not differentially affected by sex or colonic region.

CONCLUSIONS & INFERENCES

The number and volume of ICC networks in the normal human stomach and colon decline with age. This decrease in ICC likely reduces the functional capacity of the gastrointestinal motor apparatus, may contribute to changes in gastrointestinal motility with aging and may influence intestinal responses to insults such as disease, operative interventions and medications in older patients. Tissue specimens must be carefully age-matched when studying ICC in disease.

AM symbiosis alters phenolic acid content in tomato roots

Arbuscular mycorrhizal (AM) fungi colonize the roots of most plants to establish a mutualistic symbiosis leading to important benefits for plant health. We have recently shown that AM symbiosis alters both transcriptional and hormonal profiles in tomato roots, many of these changes related to plant defence. Here, we analytically demonstrate that the levels of other important defence-related compounds as phenolic acids are also altered in the symbiosis. Both caffeic and chlorogenic acid levels significantly decreased in tomato roots upon mycorrhization, while ferulic acid increased. Moreover, in the case of caffeic acid a differential reduction was observed depending on the colonizing AM fungus. The results confirm that AM associations imply the regulation of plant defence responses, and that the host changes may vary depending on the AM fungus involved. The potential implications of altered phenolic acid levels on plant control over mycorrhizal colonization and in the plant resistance to pathogens is discussed.

Simultaneous measurement of serotonin and melatonin from the intestine of old mice: the effects of daily melatonin supplementation

Ageing is associated with important changes in gastrointestinal function and in the levels of intestinal hormones secreted. Enterochromaffin (EC) cells containing serotonin (5-HT) and melatonin may play a major role in maintaining gut function during ageing. Our aim was to characterise the mucosal availability of 5-HT and melatonin in the ileum and colon of a mouse model of ageing. Female young mice (2-5 month; n = 6), aged mice (22-24 months; n = 6) and aged mice treated with melatonin (n = 6; 10 mg/kg/day) were examined. Electrochemical methods were used to measure 5-HT and melatonin concentrations near the mucosal surface of ileum and distal colon. Amperometry studies showed that steady state levels of 5-HT from ileum and colon were decreased in aged mice treated with melatonin when compared to aged mice, while compression-evoked 5-HT release was unchanged. Differential pulse voltammetry studies showed that young mice had concentrations of 5-HT of 4.8 +/- 0.8 mum in the ileum and 4.9 +/- 1.0 mum in the colon. Concentrations of melatonin were 5.7 +/- 1.4 mum in the ileum and 5.6 +/- 1.9 mum in the colon. Compared to young mice, the levels of 5-HT and melatonin were increased in aged mice (combined ileum and colon: 5-HT = 130% and melatonin = 126% of young mice) and decreased in melatonin-treated mice (5-HT = 94% and melatonin = 82%). In conclusion, our data show that the availability of gut 5-HT and melatonin is increased in aged mice and melatonin treatment suppresses natural gastrointestinal production of 5-HT and melatonin in the aged mouse intestine.

Spontaneous calcium oscillations in urinary bladder smooth muscle cells

Although spontaneous phasic activity of detrusor muscle plays an important role in urinary bladder function there is little information regarding myogenic [Ca(2+)](i) signals in this tissue. We have studied spontaneous, unstimulated [Ca(2+)](i) signals in fura-2 loaded detrusor cells isolated from newborn (10-13 days old) guinea-pig urinary bladder. In newborn guinea pigs 35% of studied muscle cells displayed spontaneous [Ca(2+)](i) oscillations with several kinetic patterns (from irregular to highly paced cycles). The oscillations were inhibited by external Ca(2+) removal, treatment with L- and T-type Ca(2+) channel blockers and by the hyperpolarizing drug pinacidil. Ca(2+) stores were necessary to maintain oscillations, as indicated by the inhibitory effects of thapsigargin, ryanodine and 2-APB. Oscillations were also inhibited by folimycin, an inhibitor of acidic Ca(2+) stores. Treatment with the selective inhibitors iberiotoxin and NPPB indicated that the oscillatory signal is also modulated by Ca(2+) -activated K(+) channels (inhibitory) and Ca(2+) -activated Cl(-) channels (stimulatory). Our results indicate that detrusor cells from newborn guinea-pigs develop spontaneous [Ca(2+)](i) oscillations due to Ca(2+) influx through T- and L-type Ca(2+) channels modulated by intracellular stores, including acidic pools. This activity could underlie the myogenic activity of urinary bladder during early stages of development.

Treatment of anaerobic sludge digester effluents by the CANON process in an air pulsing SBR

The CANON (Completely Autotrophic Nitrogen removal Over Nitrite) process was successfully developed in an air pulsing reactor type SBR fed with the supernatant from an anaerobic sludge digester and operated at moderately low temperatures (18-24 degrees C). The SBR was started up as a nitrifying reactor, lowering progressively the dissolved oxygen concentration until reaching partial nitrification. Afterwards, an inoculation with sludge containing Anammox biomass was carried out. Nitrogen volumetric removal rates of 0.25 g NL(-1)d(-1) due to Anammox activity were measured 35 d after inoculation even though the inoculum constituted only 8% (w/w) of the biomass present in the reactor and it was poorly enriched in Anammox bacteria. The maximal nitrogen removal rate was of 0.45 g NL(-1)d(-1). By working at a dissolved oxygen concentration of 0.5 mg L(-1) in the bulk liquid, nitrogen removal percentages up to 85% were achieved. The reactor presented good biomass retention capacity allowing the accumulation of 4.5 g VSS L(-1). The biomass was composed by ammonia oxidizing bacteria (AOB) forming fluffy structures and granules with an average diameter of 1.6mm. These granules were composed by Anammox bacteria located in internal anoxic layers surrounded by an external aerobic layer where AOB were placed.

Effect of age on the enteric nervous system of the human colon

The effect of age on the anatomy and function of the human colon is incompletely understood. The prevalence of disorders in adults such as constipation increase with age but it is unclear if this is due to confounding factors or age-related structural defects. The aim of this study was to determine number and subtypes of enteric neurons and neuronal volumes in the human colon of different ages. Normal colon (descending and sigmoid) from 16 patients (nine male) was studied; ages 33-99. Antibodies to HuC/D, choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), and protein gene product 9.5 were used. Effect of age was determined by testing for linear trends using regression analysis. In the myenteric plexus, number of Hu-positive neurons declined with age (slope = -1.3 neurons/mm/10 years, P = 0.03). The number of ChAT-positive neurons also declined with age (slope = -1.1 neurons/mm/10 years of age, P = 0.02). The number of nNOS-positive neurons did not decline with age. As a result, the ratio of nNOS to Hu increased (slope = 0.03 per 10 years of age, P = 0.01). In the submucosal plexus, the number of neurons did not decline with age (slope = -0.3 neurons/mm/10 years, P = 0.09). Volume of nerve fibres in the circular muscle and volume of neuronal structures in the myenteric plexus did not change with age. In conclusion, the number of neurons in the human colon declines with age with sparing of nNOS-positive neurons. This change was not accompanied by changes in total volume of neuronal structures suggesting compensatory changes in the remaining neurons.

Ano1 is a selective marker of interstitial cells of Cajal in the human and mouse gastrointestinal tract

Populations of interstitial cells of Cajal (ICC) are altered in several gastrointestinal neuromuscular disorders. ICC are identified typically by ultrastructure and expression of Kit (CD117), a protein that is also expressed on mast cells. No other molecular marker currently exists to independently identify ICC. The expression of ANO1 (DOG1, TMEM16A), a Ca(2+)-activated Cl(-) channel, in gastrointestinal stromal tumors suggests it may be useful as an ICC marker. The aims of this study were therefore to determine the distribution of Ano1 immunoreactivity compared with Kit and to establish whether Ano1 is a reliable marker for human and mouse ICC. Expression of Ano1 in human and mouse stomach, small intestine, and colon was investigated by immunofluorescence labeling using antibodies to Ano1 alone and in combination with antibodies to Kit. Colocalization of immunoreactivity was demonstrated by epifluorescence and confocal microscopy. In the muscularis propria, Ano1 immunoreactivity was restricted to cells with the morphology and distribution of ICC. All Ano1-positive cells in the muscularis propria were also Kit positive. Kit-expressing mast cells were not Ano1 positive. Some non-ICC in the mucosa and submucosa of human tissues were Ano1 positive but Kit negative. A few (3.2%) Ano1-positive cells in the human gastric muscularis propria were labeled weakly for Kit. Ano1 labels all classes of ICC and represents a highly specific marker for studying the distribution of ICC in mouse and human tissues with an advantage over Kit since it does not label mast cells.

Priming of plant innate immunity by rhizobacteria and beta-aminobutyric acid: differences and similarities in regulation

Pseudomonas fluorescens WCS417r bacteria and beta-aminobutyric acid can induce disease resistance in Arabidopsis, which is based on priming of defence. In this study, we examined the differences and similarities of WCS417r- and beta-aminobutyric acid-induced priming. Both WCS417r and beta-aminobutyric acid prime for enhanced deposition of callose-rich papillae after infection by the oomycete Hyaloperonospora arabidopsis. This priming is regulated by convergent pathways, which depend on phosphoinositide- and ABA-dependent signalling components. Conversely, induced resistance by WCS417r and beta-aminobutyric acid against the bacterial pathogen Pseudomonas syringae are controlled by distinct NPR1-dependent signalling pathways. As WCS417r and beta-aminobutyric acid prime jasmonate- and salicylate-inducible genes, respectively, we subsequently investigated the role of transcription factors. A quantitative PCR-based genome-wide screen for putative WCS417r- and beta-aminobutyric acid-responsive transcription factor genes revealed distinct sets of priming-responsive genes. Transcriptional analysis of a selection of these genes showed that they can serve as specific markers for priming. Promoter analysis of WRKY genes identified a putative cis-element that is strongly over-represented in promoters of 21 NPR1-dependent, beta-aminobutyric acid-inducible WRKY genes. Our study shows that priming of defence is regulated by different pathways, depending on the inducing agent and the challenging pathogen. Furthermore, we demonstrated that priming is associated with the enhanced expression of transcription factors.

Age-related alterations in Ca2+ signals and mitochondrial membrane potential in exocrine cells are prevented by melatonin

Information regarding age-induced Ca(2+) signal alterations in nonexcitable cells is limited. In addition, little evidence exists on the ability of melatonin to palliate the effects of aging on Ca(2+) signals and mitochondrial potential, a parameter involved in both Ca(2+) signaling and aging. We studied the ability of melatonin to prevent the effects of aging on intracellular Ca(2+) homeostasis and mitochondrial potential in exocrine cells. Pancreatic acinar cells were obtained from adult (3 months old) and aged (22-24 months old) mice by collagenase dispersion. Ca(2+) signals, in situ mitochondrial potential and in vitro amylase secretion were determined. Secretion in response to increasing levels of the secretagogues, acetylcholine and cholecystokinin (CCK), were impaired in aged pancreatic acini. This decrease was accompanied by an inhibition in the amplitude of the peak response to maximal concentrations of the agonists, and by a decrease in the pattern of Ca(2+) oscillations induced by postprandial levels of CCK. Both the size of the calcium pools, assessed by low levels of ionomycin, and capacitative calcium entry, induced by depletion of the stores with thapsigargin, were diminished in aged cells. These changes in Ca(2+) homeostasis were associated with depolarization of intracellular mitochondria. Oral administration of melatonin for 3 months to aged mice restored the secretory response, the amplitude and frequency of Ca(2+) responses, the size of intracellular calcium pools, the capacitative calcium entry, and the mitochondrial potential. In conclusion, melatonin restores secretory function, Ca(2+) signals and mitochondrial potential of aged exocrine cells.

Transcription factor MYC2 is involved in priming for enhanced defense during rhizobacteria-induced systemic resistance in Arabidopsis thaliana

Upon appropriate stimulation, plants can develop an enhanced capacity to express infection-induced cellular defense responses, a phenomenon known as the primed state. Colonization of the roots of Arabidopsis thaliana by the beneficial rhizobacterial strain Pseudomonas fluorescens WCS417r primes the leaf tissue for enhanced pathogen- and insect-induced expression of jasmonate (JA)-responsive genes, resulting in an induced systemic resistance (ISR) that is effective against different types of pathogens and insect herbivores. Here the molecular mechanism of this rhizobacteria-induced priming response was investigated using a whole-genome transcript profiling approach. Out of the 1879 putative methyl jasmonate (MeJA)-responsive genes, 442 genes displayed a primed expression pattern in ISR-expressing plants. Promoter analysis of ISR-primed, MeJA-responsive genes and ISR-primed, Pseudomonas syringae pv. tomato DC3000 (Pst DC3000)-responsive genes revealed over-representation of the G-box-like motif 5'-CACATG-3'. This motif is a binding site for the transcription factor MYC2, which plays a central role in JA- and abscisic acid-regulated signaling. MYC2 expression was consistently up-regulated in ISR-expressing plants. Moreover, mutants impaired in the JASMONATE-INSENSITIVE1/MYC2 gene (jin1-1 and jin1-2) were unable to mount WCS417r-ISR against Pst DC3000 and the downy mildew pathogen Hyaloperonospora parasitica. Together, these results pinpoint MYC2 as a potential regulator in priming for enhanced JA-responsive gene expression during rhizobacteria-mediated ISR.

Ca2+ extrusion in aged smooth muscle cells

We investigated the effects of aging in Ca(2+) extrusion mechanisms in smooth muscle bladder cells from 4 and 20-24-month-old guinea pigs using fluorescence microscopy and fura-2. Cells were challenged with a pulse of KCl immediately before perfusion with a Ca(2+) free solution containing no inhibitors (control, untreated cells) or inhibitors of plasma membrane Ca(2+) pump (PMCA, 1mM La(3+)), Na(+)/Ca(2+) exchanger (NCX, 1 microM SEA0400) or the sarcoendoplasmic Ca(2+) pump (SERCA, 1 microM thapsigargin). Treatment of young adult cells with the inhibitors allowed estimating a relative contribution of 55% for NCX, 27% for PMCA and 31% for SERCA. Combination of two inhibitors at the same time showed the presence of interaction between extrusion mechanisms. In aged cells the [Ca(2+)](i) extrusion was impaired due to decrease of PMCA activity, as revealed by the loss of effect of La(3+), and to inhibitory interactions between NCX and SERCA activities, indicated by acceleration of decay in response to their respective inhibitors. In conclusion, in smooth muscle cells aging decreases the overall Ca(2+) extrusion activity and modifies the interactions between the activities of the main Ca(2+) removing mechanisms.

Aging impairs neurogenic contraction in guinea pig urinary bladder: role of oxidative stress and melatonin

The incidence of urinary bladder disturbances increases with age, and free radical accumulation has been proposed as a causal factor. Here we investigated the association between changes in bladder neuromuscular function and oxidative stress in aging and the possible benefits of melatonin treatment. Neuromuscular function was assessed by electrical field stimulation (EFS) of isolated guinea pig detrusor strips from adult and aged female guinea pigs. A group of adult and aged animals were treated with 2.5 mg·kg−1·day−1 melatonin for 28 days. Neurotransmitter blockers were used to dissect pharmacologically the EFS-elicited contractile response. EFS induced a neurogenic and frequency-dependent contraction that was impaired by aging. This impairment is in part related to a decrease in detrusor myogenic contractility. Age also decreased the sensitivity of the contraction to pharmacological blockade of purinergic and sensitive fibers but increased the effect of blockade of nitrergic and adrenergic nerves. The density of cholinergic and nitrergic nerves remained unaltered, but aging modified afferent fibers. These changes were associated with an increased level of markers for oxidative stress. Melatonin treatment normalized oxidative levels and counteracted the aging-associated changes in bladder neuromuscular function. In conclusion, these results show that aging modifies neurogenic contraction and the functional profile of the urinary bladder plexus and simultaneously increases the oxidative damage to the organ. Melatonin reduces oxidative stress and improves the age-induced changes in bladder neuromuscular function, which could be of importance in reducing the impact of age-related bladder disorders.

Tvbgn3, a beta-1,6-glucanase from the biocontrol fungus Trichoderma virens, is involved in mycoparasitism and control of Pythium ultimum

Even though beta-1,6-glucanases have been purified from several filamentous fungi, the physiological function has not been conclusively established for any species. In the present study, the role of Tvbgn3, a beta-1,6-glucanase from Trichoderma virens, was examined by comparison of wild-type (WT) and transformant strains in which Tvbgn3 was disrupted (GKO) or constitutively overexpressed (GOE). Gene expression analysis revealed induction of Tvbgn3 in the presence of host fungal cell walls, indicating regulation during mycoparasitism. Indeed, while deletion or overexpression of Tvbgn3 had no evident effect on growth and development, GOE and GKO strains showed an enhanced or reduced ability, respectively, to inhibit the growth of the plant pathogen Pythium ultimum compared to results with the WT. The relevance of this activity in the biocontrol ability of T. virens was confirmed in plant bioassays. Deletion of the gene resulted in levels of disease protection that were significantly reduced from WT levels, while GOE strains showed a significantly increased biocontrol capability. These results demonstrate the involvement of beta-1,6-glucanase in mycoparasitism and its relevance in the biocontrol activity of T. virens, opening a new avenue for biotechnological applications.

Sm1, a proteinaceous elicitor secreted by the biocontrol fungus Trichoderma virens induces plant defense responses and systemic resistance

The soilborne filamentous fungus Trichoderma virens is a biocontrol agent with a well-known ability to produce antibiotics, parasitize pathogenic fungi, and induce systemic resistance in plants. Even though a plant-mediated response has been confirmed as a component of bioprotection by Trichoderma spp., the molecular mechanisms involved remain largely unknown. Here, we report the identification, purification, and characterization of an elicitor secreted by T. virens, a small protein designated Sm1 (small protein 1). Sm1 lacks toxic activity against plants and microbes. Instead, native, purified Sm1 triggers production of reactive oxygen species in monocot and dicot seedlings, rice, and cotton, and induces the expression of defense-related genes both locally and systemically in cotton. Gene expression analysis revealed that SM1 is expressed throughout fungal development under different nutrient conditions and in the presence of a host plant. Using an axenic hydroponic system, we show that SM1 expression and secretion of the protein is significantly higher in the presence of the plant. Pretreatment of cotton cotyledons with Sm1 provided high levels of protection to the foliar pathogen Colletotrichum sp. These results indicate that Sm1 is involved in the induction of resistance by Trichoderma spp. through the activation of plant defense mechanisms.

Mitochondrial reactive oxygen species and Ca2+ signaling

Mitochondria are an important source of reactive oxygen species (ROS) formed as a side product of oxidative phosphorylation. The main sites of oxidant production are complex I and complex III, where electrons flowing from reduced substrates are occasionally transferred to oxygen to form superoxide anion and derived products. These highly reactive compounds have a well-known role in pathological states and in some cellular responses. However, although their link with Ca(2+) is well studied in cell death, it has been hardly investigated in normal cytosolic calcium concentration ([Ca(2+)](i)) signals. Several Ca(2+) transport systems are modulated by oxidation. Oxidation increases the activity of inositol 1,4,5-trisphosphate and ryanodine receptors, the main channels releasing Ca(2+) from intracellular stores in response to cellular stimulation. On the other hand, mitochondria are known to control [Ca(2+)](i) signals by Ca(2+) uptake and release during cytosolic calcium mobilization, specially in mitochondria situated close to Ca(2+) release channels. Mitochondrial inhibitors modify calcium signals in numerous cell types, including oscillations evoked by physiological stimulus. Although these inhibitors reduce mitochondrial Ca(2+) uptake, they also impair ROS production in several systems. In keeping with this effect, recent reports show that antioxidants or oxidant scavengers also inhibit physiological calcium signals. Furthermore, there is evidence that mitochondria generate ROS in response to cell stimulation, an effect suppressed by mitochondrial inhibitors that simultaneously block [Ca(2+)](i) signals. Together, the data reviewed here indicate that Ca(2+)-mobilizing stimulus generates mitochondrial ROS, which, in turn, facilitate [Ca(2+)](i) signals, a new aspect in the biology of mitochondria. Finally, the potential implications for biological modeling are discussed.

Expression of a tomato sugar transporter is increased in leaves of mycorrhizal or Phytophthora parasitica-infected plants

A full-length cDNA clone (LeST3), encoding a putative tomato sugar transporter, was isolated from mycorrhizal roots by using a PCR-based approach. Based on sequence similarity, conserved motifs and predicted membrane topology, LeST3 was classified as a putative monosaccharide transporter of the sugar transporter subgroup of the major facilitator superfamily. Southern blot analysis showed that LeST3 represents a single-copy gene in tomato. To investigate its function, LeST3 was expressed in a hexose transport-deficient mutant of Saccharomyces cerevisiae. Although LeST3 was correctly transcribed in yeast, it did not restore growth on hexoses of the S. cerevisiae mutant. LeST3 gene expression was increased in the leaves of plants colonised by the arbuscular mycorrhizal (AM) fungi Glomus mosseae or Glomus intraradices and in those of plants infected with the root pathogen Phytophthora parasitica. These data suggest that LeST3 plays a role in the transport of sugars into the sink tissues and responds to the increased demand for carbohydrates exerted by two AM fungi and by a root pathogen to cope with the increased metabolic activity of the colonised/infected tissues or to supply carbohydrates to the AM fungus.

Non-stimulated Ca2+ leak pathway in cerebellar granule neurones

The aim of this study was to investigate the pathways of calcium influx routes in non-stimulated cerebellar granule neurones by use of standard microspectrofluorimetric techniques. Repetitive application of Ca2+-free solutions for various time intervals induced decreases of resting cytosolic free Ca2+ concentration ([Ca2+]i) which were followed, on Ca2+ readmission, by a full recovery, always to the initial resting [Ca2+]i levels. Use of drugs to deplete calcium stores (thapsigargin, alone or combined with low levels of ionomycin) did not cause release of Ca2+ from the intracellular stores nor enhanced the activity of the Ca2+ entry pathway. This influx was mainly independent of voltage operated calcium channels, since both L-type channel blockers (nitrendipine) and the hyperpolarizing agent pinacidil (a K+-channel opener) were without effect. Contribution from glutamate receptors to this influx was eliminated since a combination of blockers of NMDA and AMPA glutamate receptors (NBQX and D-AP5) did not affect the properties of the Ca2+ response. The Ca2+ leak pathway was sensitive to micromolar levels of lanthanum and gadolinium, and to the compound 2-APB, features shared by several channels of the TRP superfamily. In summary, our results show the presence of a Ca2+ permeable pathway, active and patent in resting conditions in cerebellar granule neurones, and which is different from the voltage-operated calcium channels and not operated by depletion of the stores.

Signal signature and transcriptome changes of Arabidopsis during pathogen and insect attack

Plant defenses against pathogens and insects are regulated differentially by cross-communicating signaling pathways in which salicylic acid (SA), jasmonic acid (JA), and ethylene (ET) play key roles. To understand how plants integrate pathogen- and insect-induced signals into specific defense responses, we monitored the dynamics of SA, JA, and ET signaling in Arabidopsis after attack by a set of microbial pathogens and herbivorous insects with different modes of attack. Arabidopsis plants were exposed to a pathogenic leaf bacterium (Pseudomonas syringae pv. tomato), a pathogenic leaf fungus (Alternaria brassicicola), tissue-chewing caterpillars (Pieris rapae), cell-content-feeding thrips (Frankliniella occidentalis), or phloem-feeding aphids (Myzus persicae). Monitoring the signal signature in each plant-attacker combination showed that the kinetics of SA, JA, and ET production varies greatly in both quantity and timing. Analysis of global gene expression profiles demonstrated that the signal signature characteristic of each Arabidopsis-attacker combination is orchestrated into a surprisingly complex set of transcriptional alterations in which, in all cases, stress-related genes are overrepresented. Comparison of the transcript profiles revealed that consistent changes induced by pathogens and insects with very different modes of attack can show considerable overlap. Of all consistent changes induced by A. brassicicola, Pieris rapae, and E occidentalis, more than 50% also were induced consistently by P. syringae. Notably, although these four attackers all stimulated JA biosynthesis, the majority of the changes in JA-responsive gene expression were attacker specific. All together, our study shows that SA, JA, and ET play a primary role in the orchestration of the plant's defense response, but other regulatory mechanisms, such as pathway cross-talk or additional attacker-induced signals, eventually shape the highly complex attacker-specific defense response.

Chemical mediators of gallbladder dysmotility

In order to accomplish its contribution to the digestive process, the gallbladder must contract appropriately during its emptying phases and it must be able to relax adequately for filling to occur. A variety of neuro-hormonal inputs to gallbladder smooth muscle coordinate the gallbladder emptying process with other events occurring in the bowel. Gallbladder dysmotility can disrupt the normal flow of bile to the small bowel, resulting in digestive dysfunction. In addition to this, alterations in gallbladder motility may play a role in pathological conditions, such as cholesterol gallstone formation and cholecystitis. It is still not entirely clear whether impaired gallbladder emptying is a cause or consequence of cholesterol gallstones, but recent experimental evidences demonstrate that cholesterol can directly affect the plasma membrane of gallbladder smooth muscle cells to cause impaired contraction. In addition, gallbladder emptying is impaired in acute gallbladder inflammation, probably as the result of the deleterious neural and muscular actions of inflammatory mediators such as reactive oxygen species, prostaglandins and histamine. It should also be noted that opiate treatments in critically ill patients can reduce gallbladder motility by inhibiting neurotransmitter release, and may contribute to the onset of acalculous cholecystitis, which is associated with significant morbidity in these patients.

Mitochondrial production of oxidants is necessary for physiological calcium oscillations

Mitochondrial involvement in Ca2+ signaling is thought to be due to the effect of mitochondrial Ca2+ removal from and Ca2+ release to cytosolic domains close to ryanodine and IP3 Ca2+ channels. However, mitochondria are a source of low levels of endogenous reactive oxygen species, and Ca2+ release channels are known to be redox-sensitive. In the present work, we studied the role of mitochondrial production of oxygen species in Ca2+ oscillations during physiological stimulation. Mitochondria-targeted antioxidants and mitochondrial inhibitors quickly inhibited calcium oscillations in pancreatic acinar cells stimulated by postprandial levels of the gut hormone cholecystokinin. Confocal microscopy using different redox-sensitive dyes showed that cholecystokinin-induced oscillations are associated with mitochondrial production of reactive oxygen species. This production is inhibited by application of mitochondria-targeted antioxidants and mitochondrial inhibitors. In addition, we found no correlation between inhibition of oscillations and mitochondrial depolarization. We conclude that low level production of reactive oxygen species by mitochondria is a necessary element in the development of Ca2+ oscillations during physiological stimulation. This study unveils a new and unexplored aspect of the participation of mitochondria in calcium signals.

Urinary bladder instability induced by selective suppression of the murine small conductance calcium-activated potassium (SK3) channel

Small conductance, calcium-activated potassium (SK) channels have an important role in determining the excitability and contractility of urinary bladder smooth muscle. Here, the role of the SK isoform SK3 was examined by altering expression levels of the SK3 gene using a mouse model that conditionally overexpresses SK3 channels (SK3T/T). Prominent SK3 immunostaining was found in both the smooth muscle (detrusor) and urothelium layers of the urinary bladder. SK currents were elevated 2.4-fold in isolated myocytes from SK3T/T mice. Selective suppression of SK3 expression by dietary doxycycline (DOX) decreased SK current density in isolated myocytes, increased phasic contractions of isolated urinary bladder smooth muscle strips and exposed high affinity effects of the blocker apamin of the SK isoforms (SK1-3), suggesting an additional participation from SK2 channels. The role of SK3 channels in urinary bladder function was assessed using cystometry in conscious, freely moving mice. The urinary bladders of SK3T/T had significantly greater bladder capacity, and urine output exceeded the infused saline volume. Suppression of SK3 channel expression did not alter filling pressure, threshold pressure or bladder capacity, but micturition pressure was elevated compared to control mice. However, SK3 suppression did eliminate excess urine production and caused a marked increase in non-voiding contractions. The ability to examine bladder function in mice in which SK3 channel expression is selectively altered reveals that these channels have a significant role in the control of non-voiding contractions in vivo. Activation of these channels may be a therapeutic approach for management of non-voiding contractions, a condition which characterizes many types of urinary bladder dysfunctions including urinary incontinence.

ERG K+ channels modulate the electrical and contractile activities of gallbladder smooth muscle

The current study was undertaken to test the existence and possible role of ether-a-go-go-related gene 1 (ERG1) protein K(+) channels in gallbladder smooth muscle (GBSM). Transcripts encoding ERG1 were detected in human, mouse, and guinea pig GBSM, and ERG1 immunoreactivity was observed in GBSM cells. In intracellular voltage recordings, addition of E-4031 (100 nM-1 microM) or cisapride (100 nM-2 microM) caused concentration-dependent excitation of guinea pig GBSM that was not affected by 500 nM TTX + 5 microM atropine, and E-4031 also depolarized the resting membrane potential. In muscle strip studies, E-4031 either induced phasic contractions or significantly increased the amplitude of phasic contractions in spontaneously active tissues (P = 0.001). E-4031 also potentiated bethanechol-induced contractions. In conclusion, ERG1 channels are expressed in the GBSM, where they play a role in excitation-contraction coupling probably by contributing to repolarization of the plateau phase of the action potential and to the resting membrane potential.

Localized versus systemic effect of arbuscular mycorrhizal fungi on defence responses to Phytophthora infection in tomato plants

Development of biological control for plant diseases is accepted as a durable and environmentally friendly alternative for agrochemicals. Arbuscular mycorrhizal fungi (AMF), which form symbiotic associations with root systems of most agricultural, horticultural and hardwood crop species, have been suggested as widespread potential bioprotective agents. In the present study the ability of two AMF (Glomus mosseae and Glomus intraradices) to induce local or systemic resistance to Phytophthora parasitica in tomato roots have been compared using a split root experimental system. Glomus mosseae was effective in reducing disease symptoms produced by P. parasitica infection, and evidence points to a combination of local and systemic mechanisms being responsible for this bioprotector effect. The biochemical analysis of different plant defence-related enzymes showed a local induction of mycorrhiza-related new isoforms of the hydrolytic enzymes chitinase, chitosanase and beta-1,3-glucanase, as well as superoxide dismutase, an enzyme which is involved in cell protection against oxidative stress. Systemic alterations of the activity of some of the constitutive isoforms were also observed in non-mycorrhizal roots of mycorrhizal plants. Studies on the lytic activity against Phytophthora cell wall of root protein extracts also corroborated a systemic effect of mycorrhizal symbiosis on tomato resistance to Phytophthora.

Opioid agonists inhibit excitatory neurotransmission in ganglia and at the neuromuscular junction in Guinea pig gallbladder

BACKGROUND & AIMS

Opiates administered therapeutically could have an inhibitory effect on the neuromuscular axis of the gallbladder, and thus contribute to biliary stasis and acalculous cholecystitis.

METHODS

Intracellular recordings were made from gallbladder neurons and smooth muscle, and tension measurements were made from muscle strips. Opioid receptor-specific agonists tested: delta, DPDPE; kappa, U-50488H; and mu, DAMGO.

RESULTS

Opioid agonists had no effect on gallbladder neurons or smooth muscle. Each of the opioid agonists potently suppressed the fast excitatory synaptic input to gallbladder neurons, in a concentration-dependent manner with half-maximal effective concentration values of about 1 pmol/L. Also, each agonist caused a concentration-dependent reduction in the amplitude of the neurogenic contractile response (half-maximal effective concentration values: DPDPE, 189 pmol/L; U-50488H, 472 pmol/L; and DAMGO, 112 pmol/L). These ganglionic and neuromuscular effects were attenuated by the highly selective opioid-receptor antagonist, naloxone. Opioid-receptor activation also inhibited the presynaptic facilitory effect of cholecystokinin in gallbladder ganglia. Immunohistochemistry with opioid receptor-specific antisera revealed immunostaining for all 3 receptor subtypes in nerve bundles and neuronal cell bodies within the gallbladder, whereas opiate-immunoreactive nerve fibers are sparse in the gallbladder.

CONCLUSIONS

These results show that opiates can cause presynaptic inhibition of excitatory neurotransmission at 2 sites within the wall of the gallbladder: vagal preganglionic terminals in ganglia and neuromuscular nerve terminals. These findings support the concept that opiates can contribute to gallbladder stasis by inhibiting ganglionic activity and neurogenic contractions.

Relaxation of canine gallbladder to nerve stimulation involves adrenergic and non-adrenergic non-cholinergic mechanisms

Electrical field stimulation (EFS) of dog gallbladder strips induced a frequency-dependent contractile response followed by an off-relaxation that was turned into a pure inhibitory response after atropine pretreatment. Guanethidine reduced the atropine-induced relaxing responses, so an adrenergic mechanism can partially account for the nerve-mediated gallbladder relaxation. However, guanethidine pretreatment also revealed a nonadrenergic noncholinergic (NANC) relaxation induced by EFS, which was frequency independent. NANC relaxations were reduced by L-arginine methyl ester (L-NAME, 100 micromol L-1), a nitric oxide synthase inhibitor (D-p-Cl-Phe6, Leul7; 10 micromol L-1), a vasoactive intestinal peptide (VIP) receptor antagonist, and an inhibitor of haem oxygenase, (copper protoporphyrin IX; CuPP-IX; 10 micromol L-1), suggesting that nitric oxide (NO), VIP and carbon monoxide (CO), respectively, are released in response to EFS. Immunoreactivities for haem oxygenase-2 (HO-2) and VIP, and histochemical staining for NADPH diaphorase were observed in nerve cell bodies and fibres, demonstrating the presence of CO, VIP and NO as putative NANC neurotransmitters in dog gallbladder. These data support the hypothesis that NO, VIP and CO contribute to NANC relaxation of the canine gallbladder.

A redox-based mechanism for the contractile and relaxing effects of NO in the guinea-pig gall bladder

The purpose of this study was to determine the effects of sodium nitroprusside (SNP), 2,2'-(hydroxynitrosohydrazino)bis-ethanamine (DETA/NO) and 3-morpholinosydnonimine (SIN-1), NO donors which yield different NO reactive species (NO+, NO* and peroxynitrite, respectively), as well as exogenous peroxynitrite, on gall bladder contractility. Under resting tone conditions, SNP induced a dose-dependent contraction with a maximal effect (10.3 +/- 0.7 mN, S.E.M.) at 1 mM. Consistent with these findings, SNP caused a concentration-dependent depolarization of gall bladder smooth muscle. The excitatory effects of SNP were dependent on extracellular calcium entry through L-type Ca2+ channels. Furthermore, the contraction and depolarization were sensitive to tyrosine kinase blockade, and an associated increase in tyrosine phosphorylation was detected in Western blot studies. DETA/NO induced dose-dependent relaxing effects. These relaxations were sensitive to the guanylyl cyclase inhibitor 1H-[1,2,4]oxidiazolo[4,3-a]quinoxaline-1-one (ODQ, 2 microM) but they were not altered by treatment with the potassium channel blockers tetraethylammoniun (TEA, 5 mM) and 4-aminopyridine (4-AP, 5 mM). When tested in a reducing environment (created by 2.5 mM 1,4-dithiothreitol, DTT), SNP caused a relaxation of gall bladder muscle strips. Similarly, the SNP-induced contraction was converted to a relaxation, and associated hyperpolarization, when DTT was added during the steady state of an SNP-induced response. SIN-1 (0.1 mM), which has been shown to release peroxynitrite, induced relaxing effects that were enhanced by superoxide dismutase (SOD, 50 U ml(-1)). The relaxations induced by either SIN-1 alone or SIN-1 in the presence of SOD were strengthened by catalase (1000 U ml(-1)) and abolished by ODQ pretreatment. However, exogenous peroxynitrite induced a concentration-dependent contraction, which was dependent on activation of leukotriene (LT) metabolism and extracellular calcium. The peroxynitrite-induced contraction was abolished in the presence of the peroxynitrite scavenger melatonin. These results suggest that SIN-1 behaves as an NO* rather than a peroxynitrite source. We conclude that, depending on the redox state, NO has opposing effects on the motility of the gall bladder, being a relaxing agent when in NO * form and a contracting agent when in NO+ or peroxynitrite redox species form. Knowledge of the contrasting effects of the different redox forms of NO can clarify our understanding of the effects of NO donors on gall bladder and other smooth muscle cell types.