Participation of mitochondria in calcium signalling in the exocrine pancreas

This minireview is an attempt to put together some of the recent advances regarding the implications of mitochondria in Ca2+ homeostasis. Although the main role of this cytoplasmic organelle is ATP supply to the cell, during the past years strong evidence has been accumulated supporting an active role of these organelles in Ca2+ handling by the cell. The discovery of mitochondrial specific fluorescent dyes has permitted the study of these organelles within living cells. Due to its ubiquitous localisation within the cytosol, mitochondria would play an important role in the modulation of the subcellular patterns of Ca2+ signalling, and therefore would act as modulators of Ca2+-dependent cellular processes.

Antioxidants and Neuron-Astrocyte Interplay in Brain Physiology: Melatonin, a Neighbor to Rely on

This manuscript is a review focused onto the role of astrocytes in the protection of neurons against oxidative stress and how melatonin can contribute to the maintenance of brain homeostasis. The first part of the review is dedicated to the dependence of neurons on astrocytes by terms of survival under oxidative stress conditions. Additionally, the effects of melatonin against oxidative stress in the brain and its putative role in the protection against diseases affecting the brain are highlighted. The effects of melatonin on the physiology of neurons and astrocytes also are reviewed.

Melatonin Modulates the Antioxidant Defenses and the Expression of Proinflammatory Mediators in Pancreatic Stellate Cells Subjected to Hypoxia

Pancreatic stellate cells (PSC) play a major role in the formation of fibrotic tissue in pancreatic tumors. On its side, melatonin is a putative therapeutic agent for pancreatic cancer and inflammation. In this work, the actions of melatonin on PSC subjected to hypoxia were evaluated. Reactive oxygen species (ROS) generation reduced (GSH) and oxidized (GSSG) levels of glutathione, and protein and lipid oxidation were analyzed. The phosphorylation of nuclear factor erythroid 2-related factor (Nrf2), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB), and the regulatory protein nuclear factor of kappa light polypeptide gene enhancer in B-cells inhibitor-alpha (IκBα) was studied. The expression of Nrf2-regulated antioxidant enzymes, superoxide dismutase (SOD) enzymes, cyclooxygenase 2 (COX-2), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were also studied. Total antioxidant capacity (TAC) was assayed. Finally, cell viability was studied. Under hypoxia and in the presence of melatonin generation of ROS was observed. No increases in the oxidation of proteins or lipids were detected. The phosphorylation of Nrf2 and the expression of the antioxidant enzymes catalytic subunit of glutamate-cysteine ligase, catalase, NAD(P)H-quinone oxidoreductase 1, heme oxygenase-1, SOD1, and of SOD2 were augmented. The TAC was increased. Protein kinase C was involved in the effects of melatonin. Melatonin decreased the GSH/GSSG ratio at the highest concentration tested. Cell viability dropped in the presence of melatonin. Finally, melatonin diminished the phosphorylation of NF-kB and the expression of COX-2, IL-6, and TNF-α. Our results indicate that melatonin, at pharmacological concentrations, modulates the red-ox state, viability, and the expression of proinflammatory mediators in PSC subjected to hypoxia.

Ethanol consumption as inductor of pancreatitis

Alcohol abuse is a major cause of pancreatitis, a condition that can manifest as both acute necroinflammation and chronic damage (acinar atrophy and fibrosis). Pancreatic acinar cells can metabolize ethanol via the oxidative pathway, which generates acetaldehyde and involves the enzymes alcohol dehydrogenase and possibly cytochrome P4502E1. Additionally, ethanol can be metabolized via a nonoxidative pathway involving fatty acid ethyl ester synthases. Metabolism of ethanol by acinar and other pancreatic cells and the consequent generation of toxic metabolites, are postulated to play an important role in the development of alcohol-related acute and chronic pancreatic injury. This current work will review some recent advances in the knowledge about ethanol actions on the exocrine pancreas and its relationship to inflammatory disease and cancer.

The melatonin receptor antagonist luzindole induces Ca2+ mobilization, reactive oxygen species generation and impairs trypsin secretion in mouse pancreatic acinar cells

BACKGROUND

In this work we studied the effects of the melatonin receptor-antagonist luzindole (1 μM-50 μM) on isolated mouse pancreatic acinar cells.

METHODS

Changes in intracellular free-Ca2+ concentration, reactive oxygen species production and trypsin secretion were analyzed.

RESULTS

Luzindole induced increases in [Ca2+]i that diminished CCK-8 induced Ca2+ mobilization, compared with that observed when CCK-8 was applied alone. Treatment of cells with thapsigargin (1 μM), in the absence of Ca2+ in the extracellular medium, evoked a transient increase in [Ca2+]i. The additional incubation of cells with luzindole (10 μM) failed to induce further mobilization of Ca2+. In the presence of luzindole a concentration-dependent increase in ROS generation was observed that decreased in the absence of Ca2+ or by pretreatment of cells with melatonin (100 μM). Incubation of pancreatic acinar cells with luzindole (10 μM) impaired CCK-8-induced trypsin secretion. Melatonin was unable to revert the effect of luzindole on CCK-8-induced trypsin secretion.

CONCLUSION

The melatonin receptor-inhibitor luzindole induces Ca2+-mediated pro-oxidative conditions and impairment of enzyme secretion, which creates a situation in pancreatic acinar cells that might compromise their function.

GENERAL SIGNIFICANCE

The effects of luzindole that we have observed, might be unspecific and could mislead the observations when it is used to study the actions of melatonin on the gland. Another possibility is that melatonin receptors exhibit a basal or agonist-independent activity in pancreatic acinar cells, which might be modulated by melatonin or luzindole.

Ethanol reduces kainate-evoked glutamate secretion in rat hippocampal astrocytes

In this study we have used rat hippocampal astrocytes in culture to investigate the effect of ethanol on kainate-induced glutamate secretion. Our results show that kainate (10 μM to 500 μM) stimulated glutamate release from astrocytes. Preincubation of astrocytes in the presence of ethanol induced a concentration-dependent (1mM-50mM) inhibition of glutamate release caused by stimulation of cells with 100 μM kainate. Inhibition of alcohol-dehydrogenase, by preincubation of astrocytes in the presence of 4-methylpyrazole (1mM), abolished ethanol-induced inhibition of glutamate release in response to kainate. On the other hand, preincubation of astrocytes in the presence of the antioxidant cinnamtannin B-1 (10 μM) also blocked ethanol inhibitory action on glutamate release in response to kainate. Ethanol (50mM) reduced Ca(2+) mobilization in response to kainate, whereas cinnamtannin B-1 reversed the inhibitory action of ethanol on Ca(2+) mobilization by kainate. Our results are consistent with an inhibitory action of ethanol on glutamate secretion from hippocampal astrocytes. The inhibitory effects of ethanol are probably due to its oxidative metabolization, involves reactive oxygen species production, and a lower Ca(2+) mobilization by kainate. Taking into account the pivotal role that astrocytes play within the central nervous system, especially in relation to neurons, the negative effects of ethanol on the release of glutamate might affect neuron-glia communication in the hippocampus, which might lead to functional defects in the brain.

Modulation of cell physiology under hypoxia in pancreatic cancer

In solid tumors, the development of vasculature is, to some extent, slower than the proliferation of the different types of cells that form the tissue, both cancer and stroma cells. As a consequence, the oxygen availability is compromised and the tissue evolves toward a condition of hypoxia. The presence of hypoxia is variable depending on where the cells are localized, being less extreme at the periphery of the tumor and more severe in areas located deep within the tumor mass. Surprisingly, the cells do not die. Intracellular pathways that are critical for cell fate such as endoplasmic reticulum stress, apoptosis, autophagy, and others are all involved in cellular responses to the low oxygen availability and are orchestrated by hypoxia-inducible factor. Oxidative stress and inflammation are critical conditions that develop under hypoxia. Together with changes in cellular bioenergetics, all contribute to cell survival. Moreover, cell-to-cell interaction is established within the tumor such that cancer cells and the microenvironment maintain a bidirectional communication. Additionally, the release of extracellular vesicles, or exosomes, represents short and long loops that can convey important information regarding invasion and metastasis. As a result, the tumor grows and its malignancy increases. Currently, one of the most lethal tumors is pancreatic cancer. This paper reviews the most recent advances in the knowledge of how cells grow in a pancreatic tumor by adapting to hypoxia. Unmasking the physiological processes that help the tumor increase its size and their regulation will be of major relevance for the treatment of this deadly tumor.

Arachidonic acid modulates the spatiotemporal characteristics of agonist-evoked Ca2+ waves in mouse pancreatic acinar cells

In pancreatic acinar cells analysis of the propagation speed of secretagogue-evoked Ca2+ waves can be used to examine coupling of hormone receptors to intracellular signal cascades that cause activation of protein kinase C or production of arachidonic acid (AA). In the present study we have investigated the role of cytosolic phospholipase A2 (cPLA2) and AA in acetylcholine (ACh)- and bombesin-induced Ca2+ signaling. Inhibition of cPLA2 caused acceleration of ACh-induced Ca2+ waves, whereas bombesin-evoked Ca2+ waves were unaffected. When enzymatic metabolization of AA was prevented with the cyclooxygenase inhibitor indomethacin or the lipoxygenase inhibitor nordihydroguaiaretic acid, ACh-induced Ca2+ waves were slowed down. Agonist-induced activation of cPLA2 involves mitogen-activated protein kinase (MAPK) activation. An increase in phosphorylation of p38(MAPK) and p42/44(MAPK) within 10 s after stimulation could be demonstrated for ACh but was absent for bombesin. Rapid phosphorylation of p38(MAPK) and p42/44(MAPK) could also be observed in the presence of cholecystokinin (CCK), which also causes activation of cPLA2. ACh-and CCK-induced Ca2+ waves were slowed down when p38(MAPK) was inhibited with SB 203580, whereas inhibition of p42/44(MAPK) with PD 98059 caused acceleration of ACh- and CCK-induced Ca2+ waves. The spreading of bombesin-evoked Ca2+ waves was affected neither by PD 98059 nor by SB 203580. Our data indicate that in mouse pancreatic acinar cells both ACh and CCK receptors couple to the cPLA2 pathway. cPLA2 activation occurs within 1-2 s after hormone application and is promoted by p42/44(MAPK) and inhibited by p38(MAPK). Furthermore, the data demonstrate that secondary (Ca2+-induced) Ca2+ release, which supports Ca2+ wave spreading, is inhibited by AA itself and not by a metabolite of AA.

Involvement of ryanodine-operated channels in tert-butylhydroperoxide-evoked Ca2+ mobilisation in pancreatic acinar cells

Reactive oxygen species and related oxidative damage have been implicated in the initiation of acute pancreatitis, a disease characterised in its earliest stages by disruption of intracellular Ca2+ homeostasis. The present study was carried out in order to establish the effect of the organic pro-oxidant, tert-butylhydroperoxide (tBHP), on the mobilisation of intracellular Ca2+ stores in isolated rat pancreatic acinar cells and the mechanisms underlying this effect. Cytosolic free Ca2+ concentrations ([Ca2+]c) were monitored using a digital microspectrofluorimetric system in fura-2 loaded cells. In the presence of normal extracellular Ca2+ concentrations ([Ca2+]o), perfusion of pancreatic acinar cells with 1 mmol l-1 tBHP caused a slow sustained increase in [Ca2+]c. This increase was also observed in a nominally Ca2+-free medium, indicating a release of Ca2+ from intracellular stores. Pretreatment of cells with tBHP abolished the typical Ca2+ response of both the physiological agonist CCK-8 (1 nmol l-1) and thapsigargin (TPS, 1 micromol l-1), an inhibitor of the SERCA pump, in the absence of extracellular Ca2+. Similar results were observed with carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP, 0.5 micromol l-1), a mitochondrial uncoupler. In addition, depletion of either agonist-sensitive Ca2+ pools by CCK-8 or TPS or mitochondrial Ca2+ pools by FCCP were unable to prevent the tBHP-induced Ca2+ release. By contrast, simultaneous administration of TPS and FCCP clearly abolished the tBHP-induced Ca2+ release. These results show that tBHP releases Ca2+ from agonist-sensitive intracellular stores and from mitochondria. On the other hand, simultaneous application of FCCP and of 2-aminoethoxydiphenylborane (2-APB), a blocker of IP3-mediated Ca2+ release, was unable to suppress the increase in [Ca2+]c induced by tBHP, while the application of 50 micromol l-1 of ryanodine (which is able to block the ryanodine channels) inhibits tBHP-evoked Ca2+ mobilisation. These findings indicate that tBHP releases Ca2+ from non-mitochondrial Ca2+ pools through ryanodine channels.

Sulfanilic acid increases intracellular free-calcium concentration, induces reactive oxygen species production and impairs trypsin secretion in pancreatic AR42J cells

We studied the effects of the tartrazine-metabolite sulfanilic acid on the physiology of pancreatic AR42J cells. Sulfanilic acid (1 μM-1 mM) induced a slow and progressive increase in intracellular free-calcium concentration that reached a plateau. The effect of sulfanilic acid was not concentration-dependent. Stimulation of cells with thapsigargin (1 μM) after treatment with sulfanilic acid (1 mM) induced a smaller Ca2+ response compared with that obtained with thapsigargin alone. Sulfanilic acid induced a concentration-dependent production of reactive oxygen species; however, this effect was not Ca2+-dependent. Depolarization of mitochondrial membrane potential was observed at the concentration of 1 mM sulfanilic acid. In the presence of the compound a decrease in the GSH/GSSG ratio was observed. A decrease in the expression of superoxide dismutase 2 was noted. Finally, stimulation of cells with CCK-8 led to a concentration-dependent increase of trypsin secretion that was impaired by pretreatment of cells with sulfanilic acid. Preincubation of cells with the antioxidant melatonin (100 μM) reduced the effect of sulfanilic acid on trypsin secretion. We conclude that sulfanilic acid might induce oxidative stress, which could alter Ca2+ signaling and enzyme secretion in pancreatic AR42J cells. This creates a situation potentially leading to damage of the exocrine pancreas.

Effect of xanthine oxidase-catalyzed reactive oxygen species generation on secretagogue-evoked calcium mobilization in mouse pancreatic acinar cells

In the present study we have employed fura-2 loaded isolated mouse pancreatic acinar cells to monitor the effect that xanthine oxidase (XOD)-catalyzed reactive oxygen species generation presents on Ca(2+) mobilization by the secretagogue cholecystokinin octapeptide (CCK-8). Our results show that perfusion of pancreatic acinar cells with CCK-8 at a physiological concentration (20 pM) induced low frequency oscillations in intracellular free calcium concentration ([Ca(2+)](i)) at a rate of 1 per minute; this oscillatory pattern was completely inhibited by the introduction in the perifusion medium of 20 mU/mL XOD to generate reactive oxygen species. In addition, perfusion of pancreatic acinar cells with 20 mU/mL XOD in the absence of extracellular calcium led to a transient increase in [Ca(2+)](i,) that blocked the initiation of the Ca(2+) signals in response to 20 pM CCK-8. Similarly, XOD was also able to block acetylcholine evoked Ca(2+) spikes. However, reactive oxygen species had no effect either on Ca(2+) extrusion or on re-uptake into intracellular stores, but CCK-8-evoked Ca(2+) entry was reduced by XOD. In conclusion, our results show that XOD-evoked reactive oxygen species generation leads to a reduction either of Ca(2+) mobilization, following stimulation of pancreatic acinar cells with the Ca(2+)-mobilizing agonists CCK-8 and acetylcholine, and Ca(2+) influx evoked by CCK-8 depletion of intracellular stores. The possible XOD inhibitory mechanism on Ca(2+) mobilization by agonists is discussed.

Interferences of resveratrol with fura-2-derived fluorescence in intracellular free-Ca(2+) concentration determinations

Resveratrol (3,4',5-trihydroxy-trans-stilbene) is an antioxidant widely employed in cell physiology studies. It has been reported that it interferes with fura-2-derived fluorescence, making the employment of this dye nonviable. In this work, the interference of resveratrol with fura-2 determinations of intracellular free-Ca(2+) concentration ([Ca(2+)]c) was examined. Solutions containing different concentrations of resveratrol, with or without fura-2, in the presence or in the absence of Ca(2+), were analyzed by spectrofluorimetry. AR42J tumor cells were employed to study the influence of resveratrol on fura-2 fluorescence in living cells, by single cell fluorimetry. Resveratrol impaired the detection of fura-2-fluorescence emission (510 nm) at the 340, 360 and 380 nm excitation wavelengths. Resveratrol emitted fluorescence at 510 nm when lighted at all three excitation wavelengths. In addition, resveratrol emitted fluorescence at 380 nm when excited at 340 nm. Our observations suggest that the employment of the ratiometric properties of fura-2 to follow changes in [Ca(2+)]c in the presence of resveratrol is not viable. However, we think that the 380 nm excitation light could be employed. Results could be expressed as F0/F380, where F0 is the resting fluorescence and F380 is the value of fluoresce at a certain time point. We could follow changes in [Ca(2+)]c evoked by CCK-8, and we also detected Ca(2+) mobilization by 100 µM resveratrol in AR42J cells. This investigation presents evidence demonstrating that resveratrol interferes with fura-2 fluorescence spectra. Nevertheless, a chance still exists if the 380 nm excitation wavelength is employed in the middle or low micromolar concentrations of resveratrol.

Melatonin modulates metabolic adaptation of pancreatic stellate cells subjected to hypoxia

Pancreatic stellate cells (PSCs), the main cell type responsible for the development of fibrosis in pancreatic cancer, proliferate actively under hypoxia. Melatonin has received attention as a potential antifibrotic agent due to its anti-proliferative actions on PSCs. In this work, we investigated the activation of the PI3K/Akt/mTOR pathway and the metabolic adaptations that PSCs undergo under hypoxic conditions, as well as the probable modulation by melatonin. Incubation of cells under hypoxia induced an increase in cell proliferation, and in the expression of alpha-smooth muscle actin and of collagen type 1. In addition, an increase in the phosphorylation of Akt was observed, whereas a decrease in the phosphorylation of PTEN and GSK-3b was noted. The phosphorylation of mTOR and its substrate p70 S6K was decreased under hypoxia. Treatment of PSCs with melatonin under hypoxia diminished cell proliferation, the levels of alpha-smooth muscle actin and of collagen type 1, the phosphorylation of Akt and increased phosphorylation of mTOR. Mitochondrial activity decreased in PSCs under hypoxia. A glycolytic shift was observed. Melatonin further decreased mitochondrial activity. Under hypoxia, no increase in autophagic flux was noted. However, melatonin treatment induced autophagy activation. Nevertheless, inhibition of this process did not induce detectable changes in the viability of cells treated with melatonin. We conclude that PSCs undergo metabolic adaptation under hypoxia that might help them survive and that pharmacological concentrations of melatonin modulate cell responses to hypoxia. Our results contribute to the knowledge of the mechanisms by which melatonin could modulate fibrosis within the pancreas.

Melatonin controls cell proliferation and modulates mitochondrial physiology in pancreatic stellate cells

We have investigated the effects of melatonin on major pathways related with cellular proliferation and energetic metabolism in pancreatic stellate cells. In the presence of melatonin (1 mM, 100 µM, 10 µM, or 1 µM), decreases in the phosphorylation of c-Jun N-terminal kinase and of p44/42 and an increase in the phosphorylation of p38 were observed. Cell viability dropped in the presence of melatonin. A rise in the phosphorylation of AMP-activated protein kinase was detected in the presence of 1 mM and 100 µM melatonin. Treatment with 1 mM melatonin decreased the phosphorylation of protein kinase B, whereas 100 µM and 10 µM melatonin increased its phosphorylation. An increase in the generation of mitochondrial reactive oxygen species and a decrease of mitochondrial membrane potential were noted following melatonin treatment. Basal and maximal respiration, ATP production by oxidative phosphorylation, spare capacity, and proton leak dropped in the presence of melatonin. The expression of complex I of the mitochondrial respiratory chain was augmented in the presence of melatonin. Conversely, in the presence of 1 mM melatonin, decreases in the expression of mitofusins 1 and 2 were detected. The glycolysis and the glycolytic capacity were diminished in cells treated with 1 mM or 100 µM melatonin. Increases in the expression of phosphofructokinase-1 and lactate dehydrogenase were noted in cells incubated with 100 µM, 10 µM, or 1 µM melatonin. The expression of glucose transporter 1 was increased in cells incubated with 10 µM or 1 µM melatonin. Conversely, 1 mM melatonin decreased the expression of all three proteins. Our results suggest that melatonin, at pharmacological concentrations, might modulate mitochondrial physiology and energy metabolism in addition to major pathways involved in pancreatic stellate cell proliferation.

Dietary virgin olive oil enhances secretagogue-evoked calcium signaling in rat pancreatic acinar cells

OBJECTIVE

We evaluated the long-term effects of a fat-enriched diet (virgin olive oil) on calcium mobilization and amylase secretion induced by cholecystokinin-octapeptide (CCK-8) in rat pancreatic acinar cells. Olive oil is a major component of the Mediterranean diet, and its role in human health is actively being debated.

METHODS

Weaning male Wistar rats (21 d old) were assigned to one of two experimental groups and fed for 8 wk with a commercial chow (control group) or an experimental diet (olive group) containing 100 g/kg of virgin olive oil as dietary fat. Intracellular free calcium [Ca(2+)](i) levels were determined by loading the pancreatic cells with the fluorescent ratio-metric calcium indicator Fura-2 on an inverted fluorescent microscope. For measurement of amylase secretion, cells were incubated with the appropriate secretagogue for 30 min, and amylase activities in the supernatant were determined by the Phadebas blue starch method. Analysis of variance was used to test differences between groups.

RESULTS

Compared with the control group, the CCK-8-induced increase in [Ca(2+)](i) occurred in cells from rats in the olive group (P < 0.05). This stimulatory effect of dietary virgin olive oil was observed in calcium oscillations and large [Ca(2+)](i) transients induced by low (20 pM/L) and high (10 nM/L) concentrations of CCK-8, respectively. In addition to the effects of dietary virgin olive oil on calcium mobilization, it increased (P < 0.05) amylase secretion in response to CCK-8. Olive oil treatment did not significantly alter resting [Ca(2+)](i) or amylase release values compared with the control group. Similar results were obtained when pancreatic acinar cells were stimulated with a high concentration of acetylcholine (10 microM/L).

CONCLUSION

The present results demonstrate that a diet supplemented with virgin olive oil can modify pancreatic cell function as assessed by [Ca(2+)](i) mobilization and amylase release evoked by secretagogues in rat pancreatic acinar cells. A role for fatty acids in calcium signaling is suggested.

The melatonin receptor antagonist luzindole induces the activation of cellular stress responses and decreases viability of rat pancreatic stellate cells

In this study, we have examined the effects of luzindole, a melatonin receptor-antagonist, on cultured pancreatic stellate cells. Intracellular free-Ca2+ concentration, production of reactive oxygen species (ROS), activation of mitogen-activated protein kinases (MAPK), endoplasmic reticulum stress and cell viability were analyzed. Stimulation of cells with the luzindole (1, 5, 10 and 50 μm) evoked a slow and progressive increase in intracellular free Ca2+ ([Ca2+ ]i ) towards a plateau. The effect of the compound on Ca2+ mobilization depended on the concentration used. Incubation of cells with the sarcoendoplasmic reticulum Ca2+ -ATPase inhibitor thapsigargin (1 μm), in the absence of Ca2+ in the extracellular medium, induced a transient increase in [Ca2+ ]i . In the presence of thapsigargin, the addition of luzindole to the cells failed to induce further mobilization of Ca2+ . Luzindole induced a concentration-dependent increase in ROS generation, both in the cytosol and in the mitochondria. This effect was smaller in the absence of extracellular Ca2+ . In the presence of luzindole the phosphorylation of p44/42 and p38 MAPKs was increased, whereas no changes in the phosphorylation of JNK could be noted. Moreover, the detection of the endoplasmic reticulum stress-sensor BiP was increased in the presence of luzindole. Finally, viability was decreased in cells treated with luzindole. Because cellular membrane receptors for melatonin have not been detected in pancreatic stellate cells, we conclude that luzindole could exert direct effects that are not mediated through its action on melatonin membrane receptors.

Regulator of G-protein signaling 14 protein modulates Ca²+ influx through Cav1 channels

Calcium flux through L-type voltage-activated calcium (Cav1) channels is crucial for regulating brain functions including memory formation and behavior. Alterations in Ca²+ homeostasis have been linked to many cognitive disorders, and understanding the regulation of this process is crucial for their remedy. Therefore, here, we have evaluated the effect of a multifunctional protein known to be involved in memory functions called regulator of G-protein signaling 14 (RGS-14) on Cav1 channel activity in neuronal cell lines NG108-15 and SH-SY5Y. RGS-14 protein produced significant reduction in Ca²+ influx in both cell lines and this effect was dependent on nifedipine-sensitive Cav1 channels. Thus, our results provide evidence supporting the idea that RGS-14 may facilitate the cognitive processing by modulating Cav1 channel-mediated intracellular Ca²+ transients.

Effect of tartrazine on digestive enzymatic activities: in vivo and in vitro studies

Tartrazine (E102) is a synthetic food coloring, which belongs to the class of mono azo dyes and is known to cause numerous health problems. The current research aimed to evaluate the effect of this food dye on the enzymatic activity of amylase, lipase and proteases after a subchronic ingestion in Swiss mice. Additionally, an in vitro digestion model was used to highlight the relationship between the probable toxicity of tartrazine and the nature of the food ingested. The results show that there were no adverse effects of tartrazine on the body weight gain, and on amylase or lipase activities. However, in the high dose of tartrazine (0.05%) group, a significant decrease in trypsin and chymotrypsin enzymatic activities were observed. Regarding the in vitro digestion model, our findings show that there were no changes in the trypsin and chymotrypsin enzymatic activities either using 7.5 or 75 mg of tartrazine mixed with rice, butter or milk. We conclude that excessive consumption of tartrazine appears to alter the enzymatic activity of proteases in vivo which may have deleterious consequences on digestion. Even thought the dose close to the acceptable daily intake does not affect those activities, a strict control of tartrazine dose in high-consumption foods especially among children is an indispensable task.

Histamine does not potentiate cyclic AMP-mediated amylase secretion in the guinea-pig pancreatic acinar cells

1. This study investigates the interaction between histamine and the adenylate cyclase systems involved in the secretion of amylase in isolated guinea-pig pancreatic acinar cells. 2. Histamine caused does-related enhancement of amylase release. Similarly, incubation of acini with increasing concentrations of vasoactive intestinal peptide (VIP) resulted in a typical dose-dependent increase in amylase output. 3. When pancreatic acinar cells were incubated with histamine in combination with VIP, amylase secretion did not differ statistically from secretion induced by histamine or VIP alone and was significantly lower than theoretical additivity. Additionally, amylase secretion in the presence of histamine plus forskolin was significantly less than additive. The action of histamine was equally effective as VIP in causing cyclic adenosine monophosphate (cAMP) increase. 4. These results indicate that histamine may exert its secretory effects via the cyclic AMP pathway in the exocrine guinea-pig pancreas.

Reciprocal changes in intracellular and extracellular magnesium in rat pancreatic acinar cells in response to different secretagogues

This study employs the fluorescent bioprobe Mag-fura-2 to measure the mobilisation of magnesium (Mg2+) in rat pancreatic acinar cells at rest and during stimulation with either cholecystokinin-octapeptide (CCK-8; 10(-8) M), acetylcholine (ACh; 10(-5) M) or histamine (10(-4) M). In Mag-fura-2 loaded acini suspended in normal Krebs-Ringer-Hepes (KRH) solution containing (mMol/litre) NaCL, 130; KCI, 5; HEPES, 20; KH2PO4, 1.2; CaCl2, 1.0; MgSO4, 1.0; glucose, 10; minimum essential medium, 1.0 ml/Litre and pH 7.4, both CCK-8 and ACh evoked a transient rise in intracellular free Mg2+ concentration ([Mg2+]i) followed by a sustained and prolonged decrease. Addition of CCK-8 to acinar cell suspension previously stimulated with ACh resulted in little or no change in [Mg2+]i indicating that the two secretagogues are mobilising magnesium from the same intracellular pool. Histamine had no significant effect on [Mg2+]i or on the CCK-8 evoked response. When acini were challenged in the presence of the cell-impermeant form of Mag-fura-2 (the tetrapotassium salt) in a Ca(2+)-free KRH solution containing 1-mM EGTA, CCK-8 and ACh, stimulation resulted in a gradual release of magnesium reaching a maximum after 300-350 s following application of the secretagogues (magnesium efflux). Again histamine had no effect on magnesium release. Incubation of acinar cells in a nominally magnesium-free KRH solution had no effect on basal [Mg2+]o. When challenged with CCK-8, [Mg2+]i rose transiently, followed by a sustained decrease. In contrast, ACh stimulation resulted in a triphasic response comprising an initial rise followed by a decrease, superceded by a small rise in [Mg2+]i. Again histamine had no effect on [Mg2+]i in nominally magnesium-free solution. Addition of either ACh or CCK-8 to cells placed in KRH solution with no added Mg2+ caused a small efflux of magnesium, as measured in the presence of the tetrapotassium salt of Mag-fura-2 (cell-impermeant form). These results, employing two different forms of a fluorescent bioprobe for the measurement of magnesium, indicate that unlike histamine, CCK-8 and ACh can evoke marked changes in intracellular free magnesium concentration during the stimulus-secretion coupling process.

In vitro digestion and culture in Caco-2 cells to assess the bioavailability of fatty acids: A case study in meat matrix enriched with ω-3 microcapsules

This work aimed to evaluate the Caco-2 cells as a model to study the epithelial transport of intestinal lipid extracts subjected to in vitro digestion, to establish a standard protocol for the determination of bioaccessibility and bioavailability of fatty acids in meat matrix, especially in those enriched with ω-3 (eicosapentaenoic (EPA) and docosahexaenoic acids (DHA)). Samples were first subjected to in vitro digestion, and then, the intestinal extract was incubated with Caco-2 cells. A first trial was conducted to select the most influencing variables on the fatty acid transport during Caco-2 cell incubation: fat quantity on the intestinal extract, incubation time, and shaking. Then, a second experiment was carried out to determine the influence of these variables, being the fat quantity and the incubation time the most influencing factors on the transport and bioavailability of fatty acids. The effect of shaking was not so marked but seemed to improve the bioavailability of saturated fatty acids. This study also allows establishing the most suitable conditions: intestinal extracts with 30 mg of fat, longer incubation times (8 h), and shaking, achieving active and passive fatty acid transport without compromising the integrity of the Caco-2 cell monolayer. The accurate results obtained for major and minor fatty acids, especially EPA and DHA are remarkable, due to the interest in these bioactive compounds. Thus, this study provides a combined protocol based on static in vitro digestion followed by Caco-2 cell incubation to assess the bioaccessibility and bioavailability of fatty acids in meat samples.