Ca2+ signaling in pancreatic acinar cells: physiology and pathophysiology

The pancreatic acinar cell is a classical model for studies of secretion and signal transduction mechanisms. Because of the extensive endoplasmic reticulum and the large granular compartment, it has been possible - by direct measurements - to obtain considerable insights into intracellular Ca2+ handling under both normal and pathological conditions. Recent studies have also revealed important characteristics of stimulus-secretion coupling mechanisms in isolated human pancreatic acinar cells. The acinar cells are potentially dangerous because of the high intra-granular concentration of proteases, which become inappropriately activated in the human disease acute pancreatitis. This disease is due to toxic Ca2+ signals generated by excessive liberation of Ca2+ from both the endoplasmic reticulum and the secretory granules.

Calcium imaging demonstrates colocalization of calcium influx and extrusion in fly photoreceptors

During illumination, Ca2+ enters fly photoreceptor cells through light-activated channels that are located in the rhabdomere, the compartment specialized for phototransduction. From the rhabdomere, Ca2+ diffuses into the cell body. We visualize this process by rapidly imaging the fluorescence in a cross section of a photoreceptor cell injected with a fluorescent Ca2+ indicator in vivo. The free Ca2+ concentration in the rhabdomere shows a very fast and large transient shortly after light onset. The free Ca2+ concentration in the cell body rises more slowly and displays a much smaller transient. After ≈400 ms of light stimulation, the Ca2+ concentration in both compartments reaches a steady state, indicating that thereafter an amount of Ca2+, equivalent to the amount of Ca2+ flowing into the cell, is extruded. Quantitative analysis demonstrates that during the steady state, the free Ca2+ concentration in the rhabdomere and throughout the cell body is the same. This shows that Ca2+ extrusion takes place very close to the location of Ca2+ influx, the rhabdomere, because otherwise gradients in the steady-state distribution of Ca2+ should be measured. The close colocalization of Ca2+ influx and Ca2+ extrusion ensures that, after turning off the light, Ca2+ removal from the rhabdomere is faster than from the cell body. This is functionally significant because it ensures rapid dark adaptation.

Hypertensive effects of the iv administration of picomoles of ouabain

Ouabain, an endogenous digitalis compound, has been detected in nanomolar concentrations in the plasma of several mammals and is associated with the development of hypertension. In addition, plasma ouabain is increased in several hypertension models, and the acute or chronic administration of ouabain increases blood pressure in rodents. These results suggest a possible association between ouabain and the genesis or development and maintenance of arterial hypertension. One explanation for this association is that ouabain binds to the α-subunit of the Na+ pump, inhibiting its activity. Inhibition of this pump increases intracellular Na+, which reduces the activity of the sarcolemmal Na+/Ca2+ exchanger and thereby reduces Ca2+ extrusion. Consequently, intracellular Ca2+ increases and is taken up by the sarcoplasmic reticulum, which, upon activation, releases more calcium and increases the vascular smooth muscle tone. In fact, acute treatment with ouabain enhances the vascular reactivity to vasopressor agents, increases the release of norepinephrine from the perivascular adrenergic nerve endings and promotes increases in the activity of endothelial angiotensin-converting enzyme and the local synthesis of angiotensin II in the tail vascular bed. Additionally, the hypertension induced by ouabain has been associated with central mechanisms that increase sympathetic tone, subsequent to the activation of the cerebral renin-angiotensin system. Thus, the association with peripheral mechanisms and central mechanisms, mainly involving the renin-angiotensin system, may contribute to the acute effects of ouabain-induced elevation of arterial blood pressure.

Peroxynitrite mediates disruption of Ca2+ homeostasis by carbon monoxide via Ca2+ ATPase degradation

CO stimulates formation of NO and reactive oxygen species which, via peroxynitrite formation, inhibit Ca(2+) extrusion via PMCA, leading to disruption of Ca(2+) signaling. We propose this contributes to the neurological damage associated with CO toxicity.

Plasma membrane-associated annexin A6 reduces Ca2+ entry by stabilizing the cortical actin cytoskeleton

The annexins are a family of Ca(2+)- and phospholipid-binding proteins, which interact with membranes upon increase of [Ca(2+)](i) or during cytoplasmic acidification. The transient nature of the membrane binding of annexins complicates the study of their influence on intracellular processes. To address the function of annexins at the plasma membrane (PM), we fused fluorescent protein-tagged annexins A6, A1, and A2 with H- and K-Ras membrane anchors. Stable PM localization of membrane-anchored annexin A6 significantly decreased the store-operated Ca(2+) entry (SOCE), but did not influence the rates of Ca(2+) extrusion. This attenuation was specific for annexin A6 because PM-anchored annexins A1 and A2 did not alter SOCE. Membrane association of annexin A6 was necessary for a measurable decrease of SOCE, because cytoplasmic annexin A6 had no effect on Ca(2+) entry as long as [Ca(2+)](i) was below the threshold of annexin A6-membrane translocation. However, when [Ca(2+)](i) reached the levels necessary for the Ca(2+)-dependent PM association of ectopically expressed wild-type annexin A6, SOCE was also inhibited. Conversely, knockdown of the endogenous annexin A6 in HEK293 cells resulted in an elevated Ca(2+) entry. Constitutive PM localization of annexin A6 caused a rearrangement and accumulation of F-actin at the PM, indicating a stabilized cortical cytoskeleton. Consistent with these findings, disruption of the actin cytoskeleton using latrunculin A abolished the inhibitory effect of PM-anchored annexin A6 on SOCE. In agreement with the inhibitory effect of annexin A6 on SOCE, constitutive PM localization of annexin A6 inhibited cell proliferation. Taken together, our results implicate annexin A6 in the actin-dependent regulation of Ca(2+) entry, with consequences for the rates of cell proliferation.

Taurine Supplementation Increases K(atp) Channel Protein Content, Improving Ca2+ Handling And Insulin Secretion In Islets From Malnourished Mice Fed On A High-fat Diet.

Pancreatic β-cells are highly sensitive to suboptimal or excess nutrients, as occurs in protein-malnutrition and obesity. Taurine (Tau) improves insulin secretion in response to nutrients and depolarizing agents. Here, we assessed the expression and function of Cav and KATP channels in islets from malnourished mice fed on a high-fat diet (HFD) and supplemented with Tau. Weaned mice received a normal (C) or a low-protein diet (R) for 6 weeks. Half of each group were fed a HFD for 8 weeks without (CH, RH) or with 5% Tau since weaning (CHT, RHT). Isolated islets from R mice showed lower insulin release with glucose and depolarizing stimuli. In CH islets, insulin secretion was increased and this was associated with enhanced KATP inhibition and Cav activity. RH islets secreted less insulin at high K(+) concentration and showed enhanced KATP activity. Tau supplementation normalized K(+)-induced secretion and enhanced glucose-induced Ca(2+) influx in RHT islets. R islets presented lower Ca(2+) influx in response to tolbutamide, and higher protein content and activity of the Kir6.2 subunit of the KATP. Tau increased the protein content of the α1.2 subunit of the Cav channels and the SNARE proteins SNAP-25 and Synt-1 in CHT islets, whereas in RHT, Kir6.2 and Synt-1 proteins were increased. In conclusion, impaired islet function in R islets is related to higher content and activity of the KATP channels. Tau treatment enhanced RHT islet secretory capacity by improving the protein expression and inhibition of the KATP channels and enhancing Synt-1 islet content.

Resistência mecânica de hidrogéis termo-sensíveis constituídos de Alginato-Ca2+ / PNIPAAm, tipo Semi-IPN

Thermosensitive hydrogels were synthesized using alginate-Ca2+ in association with a thermosensitive polymer, such as PNIPAAm. The mechanical properties of the hydrogels were determined measuring the maximum tension of deformation. With the increase of the temperature by 25 to 40 ºC above the LCST the chains of PNIPAAm collapsed, dragging the alginate net and diminishing the size of the pores. The decrease in the size of the pores of the hydrogel was followed by an increase in the mechanicals resistance of the material.

Cation size effects-modified phase and PTCR development in Er3+ and Ca2+ co-doped BaTiO3 ceramics during sintering

Development of the positive temperature coefficient of resistivity (PTCR) in Er3+ and Ca2+ co-doped ferroelectric BaTiO3 was studied in this work, with Er3+ being used to act as a donor doping. Irrespective of all the materials showing high densities after sintering at 1200 to 1300 ºC, these revealed insulator at the lowest sintering temperature, changing to semiconducting and PTCR-type materials only when the sintering temperature was further increased. Observations from X-ray diffraction help correlating this effect with phase development in this formulated (Ba,Ca,Er)TiO3 system, considering the formation of initially two separated major (Ba,Ca)TiO3- and minor (Ca,Er)TiO3-based compounds, as a consequence of cation size-induced stress energy effects. Thus, appearance and enhancement here of the semiconducting and PTCR responses towards higher sintering temperatures particularly involve the incorporation of Er3+ into the major phase, rendering finally possible the generation and "percolative-like" migration of electrons throughout the whole material.

Volatile compounds in the thermoplastic extrusion of bovine rumen

The volatile compounds of raw and extruded bovine rumen, extracted by dynamic headspace, were separated by gas chromatography and analyzed by GC-MS. Raw and extruded materials presented thirty-two volatile compounds. The following compounds were identified in raw bovine rumen: heptane, 1-heptene, 4-methyl-2-pentanone, toluene, hexanal, ethyl butyrate, o-xylene, m-xylene, p-xylene, heptanal, limonene, nonanal, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane and octadecane. The following compounds were identified in the extruded material: 1-heptene, 2,4-dimethylhexane, toluene, limonene, undecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane and nonadecane. Mass spectra of some unidentified compounds indicated the presence of hydrocarbons with branched chains or cyclic structure.

Recovery and upgrading bovine rumen protein by extrusion: effect of lipid content on protein disulphide cross-linking, solubility and molecular weight

Bovine rumen protein with two levels of residual lipids (1.9 per cent or 3.8 per cent) was subjected to thermoplastic extrusion under different temperatures and moisture contents. Protein solubility in different buffers, disulphide cross-linking and molecular weight distribution were determined on the extrudates. After extrusion, samples with 1.9 per cent residual lipids content had a higher concentration of protein insoluble by undetermined forces, irrespective of feed moisture and processing temperature used. Lipid content of 3.8 per cent in the feed material resulted in more protein participating in the extrudate network through non-covalent interactions (hydrophobic and electrostatic) and disulphide bonds. A small dependency of the extrusion process on moisture and temperature and a marked dependency on lipid content, especially phospholipid, was observed, Electrophoresis under non-reducing conditions showed that protein extrusion with low feed moisture promoted high molecular breakdown inside the barrel, probably due to intense shear force, and further protein aggregation at the die end

Sugarcane bagasse cellulose/HDPE composites obtained by extrusion

Natural fibers used in this study were both pre-treated and modified residues from sugarcane bagasse. Polymer of high density polyethylene (HDPE) was employed as matrix in to composites, which were prodUced by mixing high density polyethylene with cellulose (10%) and Cell/ZrO(2)center dot nH(2)O (10%), using an extruder and hydraulic press. Tensile tests showed that the Cell/ZrO(2)center dot nH(2)O (10%)/HDPE composites present better tensile strength than cellulose (10%)/HDPE composites. Cellulose agglomerations were responsible for poor adhesion between fiber and matrix in cellulose (10%)/HDPE composites. HDPF/natural fibers composites showed also lower tensile strength in comparison to the polymer. The increase in Young`s modulus is associated to fibers reinforcement. SEM analysis showed that the cellulose fibers insertion in the matrix Caused all increase of defects, which were reduced When modified cellulose fibers were Used. (C) 2008 Elsevier Ltd. All rights reserved.

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment.

Development and Characterization of L-Alanyl-L-Glutamine Containing Pellets employing Extrusion-Spheronization Method and Drying Process in Fluidized Bad Equipment"". In this work, five formulations of L-alanyl-L-glutamine (glutamine dipeptide) containing pellets with different drug concentration were developed and evaluated: F1 (9.07%); F2 (17.70%); F3 (27.98%); F4 (37.74%) e F5 (47.53%). Pellets were prepared by extrusion-spheronization method and, further, dried in fluidized bad equipment. The following assays were carried out with the batches obtained: granulometry, friability, true density and morphologic analysis. Between the five formulations evaluated, pellets obtained from F3 present best yield (75.80%), most uniform particle size distribution (89.67% of pellets with size in the range of 0.80 to 1.18), most high true density (2.1634 g/ml) and best aspect (1.0795 +/- 0.0410). Due to these features, pellets obtained from F3 were considered adequate to further polymeric coating process in order to produce a multiparticulate system to prolong L-alanyl-L-glutamine release.