95/05032 Nonpremixed turbulent reacting flow near extinction

95/05039 Propagation and extinction of forced opposed flow smolder waves

Does Injected CO2 Affect (Chemical) Reservoir System Integrity? - A Comprehensive Experimental Approach

Chemical weathering in a tropical watershed, Luquillo Mountains, Puerto Rico III: quartz dissolution rates

Dissolution Kinetics of Iron Carbonate, Illite and Labradorite – CO2-Saline Fluid-mineral Experiments within the GaMin’11 Inter-laboratory Comparison Exercise

SO2–CO2 and pure CO2 reactivity of ferroan carbonates at carbon storage conditions

Smooth muscle cells were cultured from rat thoracic aorta and labeled to a stable specific activity with 45Ca2+, myo-[2-3H]inositol, or 32Pi. The efflux of 45Ca2+ was monitored over 10-sec intervals. Angiotensin II (AII) increased the amount of 45Ca2+ lost by 5-fold in the first 10-sec interval after the addition of AII and by 10-fold in the second 10-sec interval. AII-stimulated 45Ca2+ release was blocked by the angiotensin antagonist [1-sarcosine, 8-leucine]AII and by La3+. The removal of external Ca2+ had no effect on AII-stimulated 45Ca2+ release. Depolarization with high external K+ only slightly increased 45Ca2+ efflux and had no effect on AII-induced 45Ca2+ release. AII had no effect on the initial rate of 45Ca2+ influx. These results indicate that the rapid 45Ca2+ efflux evoked by AII is probably due to the release of 45Ca2+ sequestered intracellularly rather than to an increase in the Ca2+ permeability of the plasma membrane. AII provoked rapid increases in the levels of phosphatidic acid and phosphoinositides in the cells. These increases in phospholipids were associated with increases in phospholipase C-generated inositol phosphates (tri-, di-, and mono-). It appears that AII simultaneously increases phosphoinositide hydrolysis and synthesis in vascular smooth muscle, and both phospholipid effects may contribute to inositol triphosphate generation, which was sufficiently rapid to have a role in intracellular Ca2+ mobilization.

Hydrogen gas (H2) has a possible signaling role in many developmental and adaptive plant responses, including mitigating the harmful effects of cadmium (Cd) uptake from soil. We used electrophysiological and molecular approaches to understand how H2 ameliorates Cd toxicity in pak choi (Brassica campestrisssp. chinensis). Exposure of pak choi roots to Cd resulted in a rapid increase in the intracellular H2 production. Exogenous application of hydrogen-rich water (HRW) resulted in a Cd-tolerant phenotype, with reduced net Cd uptake and accumulation. We showed that this is dependent upon the transport of calcium ions (Ca2+) across the plasma membrane and apoplastic generation of hydrogen peroxide (H2O2) by respiratory burst oxidase homolog (BcRbohD). The reduction in root Cd uptake was associated with the application of exogenous HRW or H2O2 This reduction was abolished in the iron-regulated transporter1 (Atirt1) mutant of Arabidopsis (Arabidopsis thaliana), and pak choi pretreated with HRW showed decreased BcIRT1 transcript levels. Roots exposed to HRW had rapid Ca2+ influx, and Cd-induced Ca2+ leakage was alleviated. Two Ca2+ channel blockers, gadolinium ion (Gd3+) and lanthanum ion (La3+), eliminated the HRW-induced increase in BcRbohD expression, H2O2 production, and Cd2+ influx inhibition. Collectively, our results suggest that the Cd-protective effect of H2 in plants may be explained by its control of the plasma membrane-based NADPH oxidase encoded by RbohD, which operates upstream of IRT1 and regulates root Cd uptake at both the transcriptional and functional levels. These findings provide a mechanistic explanation for the alleviatory role of H2 in Cd accumulation and toxicity in plants.

Mitochondrial (m) Ca2+ influx is largely dependent on membrane potential (ΔΨm), whereas mCa2+ efflux occurs primarily via Ca2+ ion exchangers. We probed the kinetics of Ca2+/H+ exchange (CHEm) in guinea pig cardiac muscle mitochondria. We tested if net mCa2+ flux is altered during a matrix inward H+ leak that is dependent on matrix H+ pumping by ATPm hydrolysis at complex V (FOF1-ATPase). We measured [Ca2+]m, extra-mitochondrial (e) [Ca2+]e, ΔΨm, pHm, pHe, NADH, respiration, ADP/ATP ratios, and total [ATP]m in the presence or absence of protonophore dinitrophenol (DNP), mitochondrial uniporter (MCU) blocker Ru360, and complex V blocker oligomycin (OMN). We proposed that net slow influx/efflux of Ca2+ after adding DNP and CaCl2 is dependent on whether the ΔpHm gradient is/is not maintained by reciprocal outward H+ pumping by complex V. We found that adding CaCl2 enhanced DNP-induced increases in respiration and decreases in ΔΨm while [ATP]m decreased, ΔpHm gradient was maintained, and [Ca2+]m continued to increase slowly, indicating net mCa2+ influx via MCU. In contrast, with complex V blocked by OMN, adding DNP and CaCl2 caused larger declines in ΔΨm as well as a slow fall in pHm to near pHe while [Ca2+]m continued to decrease slowly, indicating net mCa2+ efflux in exchange for H+ influx (CHEm) until the ΔpHm gradient was abolished. The kinetics of slow mCa2+ efflux with slow H+ influx via CHEm was also observed at pHe 6.9 vs. 7.6 by the slow fall in pHm until ΔpHm was abolished; if Ca2+ reuptake via the MCU was also blocked, mCa2+ efflux via CHEm became more evident. Of the two components of the proton electrochemical gradient, our results indicate that CHEm activity is driven largely by the ΔpHm chemical gradient with H+ leak, while mCa2+ entry via MCU depends largely on the charge gradient ΔΨm. A fall in ΔΨm with excess mCa2+ loading can occur during cardiac cell stress. Cardiac cell injury due to mCa2+ overload may be reduced by temporarily inhibiting FOF1-ATPase from pumping H+ due to ΔΨm depolarization. This action would prevent additional slow mCa2+ loading via MCU and permit activation of CHEm to mediate efflux of mCa2+.HIGHLIGHTS-We examined how slow mitochondrial (m) Ca2+ efflux via Ca2+/H+ exchange (CHEm) is triggered by matrix acidity after a rapid increase in [Ca2+]m by adding CaCl2 in the presence of dinitrophenol (DNP) to permit H+ influx, and oligomycin (OMN) to block H+ pumping via FOF1-ATP synthase/ase (complex V).-Declines in ΔΨm and pHm after DNP and added CaCl2 were larger when complex V was blocked.-[Ca2+]m slowly increased despite a fall in ΔΨm but maintained pHm when H+ pumping by complex V was permitted.-[Ca2+]m slowly decreased and external [Ca2+]e increased with declines in both ΔΨm and pHm when complex V was blocked.-ATPm hydrolysis supports a falling pHm and redox state and promotes a slow increase in [Ca2+]m.-After rapid Ca2+ influx due to a bolus of CaCl2, slow mCa2+ efflux by CHEm occurs directly if pHe is low.

Growth hormone (GH) is an important mitogenic stimulus for the insulin-producing beta-cell. We investigated the effects of GH on Ca(2+) handling and diacylglycerol (DAG) and cAMP formation in the beta-cell. GH elicited a rapid increase in the cytoplasmic free [Ca(2+)], which required extracellular Ca(2+) and was also blocked by pertussis toxin or protein kinase C (PKC) inhibition. GH also elevated islet DAG content, which should lead to PKC activation. Pertussis toxin and PKC inhibitors obliterated the mitogenicity of GH, suggesting involvement of GTP-binding proteins. PKC activation stimulated beta-cell proliferation, and it also activated phospholipase D. Islet cAMP content was not elevated by GH. Addition of a specific protein kinase A antagonist failed to influence the mitogenicity of GH, whereas a stimulatory cAMP agonist stimulated beta-cell replication. We conclude that GH rapidly increases the beta-cell cytoplasmic free [Ca(2+)] and also evokes a similar increase in DAG content via a phosphatidylcholine-specific phospholipase C, but does not affect mitogen-activated protein kinases, phospholipase D, or the cAMP signaling pathway. This rise in DAG may be of importance in translation of the stimulatory signal of GH into a proliferative response by the beta-cell, which seems to occur through GTP-binding proteins and PKC-dependent mechanisms.

Rapid Ca 2+-dependent increase in oxygen consumption by mitochondria in single mammalian central neurons

Formyl-Met-Leu-Phe induces calcium-dependent tyrosine phosphorylation of Rel-1 in neutrophils

PhTX2, one of the components of the venom of the South American spider Phoneutria nigriventer, inhibits the closure of voltage-sensitive Na+ channels. Incubation of cerebral-cortical synaptosomes with PhTX2 causes a rapid increase in the intrasynaptosomal free Ca2+ concentration and a dose-dependent release of glutamate. This release is made up of a slow component, which appears to be due to reversal of Na(+)-dependent glutamate uptake, and more rapid component that is dependent on the entry of extrasynaptosomal Ca2+. It has previously been shown that membrane depolarization using KCl can cause rapid Ca(2+)-dependent release of glutamate from synaptosomes. This requires Ca2+ entry through a specific type of Ca2+ channel that is sensitive to Aga-GI, a toxic component of the venom of the spider Agelenopsis aperta. We have compared the effects of PhTX2 and KCl on elevation of intrasynaptosomal free Ca2+ and glutamate release, and a number of differences have emerged. Firstly, PhTX2-mediated Ca2+ influx and glutamate release, but not those caused by KCl, are inhibited by tetrodotoxin. Secondly, KCl produces a clear additional increase in Ca2+ and glutamate release following those elicited by PhTX2. Finally, 500 microM MnCl2 abolishes PhTX2-mediated, but not KCl-mediated, glutamate release. These findings suggest that more than one mechanism of Ca2+ entry may be coupled to glutamate release from nerve endings.

Stimulation of hepatocytes with vasopressin evokes increases in cytosolic free Ca2+ ([Ca2+]c) that are relayed into the mitochondria, where the resulting mitochondrial Ca2+ ([Ca2+]m) increase regulates intramitochondrial Ca2+-sensitive targets. To understand how mitochondria integrate the [Ca2+]c signals into a final metabolic response, we stimulated hepatocytes with high vasopressin doses that generate a sustained increase in [Ca2+]c. This elicited a synchronous, single spike of [Ca2+]m and consequent NAD(P)H formation, which could be related to changes in the activity state of pyruvate dehydrogenase (PDH) measured in parallel. The vasopressin-induced [Ca2+]m spike evoked a transient increase in NAD(P)H that persisted longer than the [Ca2+]m increase. In contrast, PDH activity increased biphasically, with an initial rapid phase accompanying the rise in [Ca2+]m, followed by a sustained secondary activation phase associated with a decline in cellular ATP. The decline of NAD(P)H in the face of elevated PDH activity occurred as a result of respiratory chain activation, which was also manifest in a calcium-dependent increase in the membrane potential and pH gradient components of the proton motive force (PMF). This is the first direct demonstration that Ca2+-mobilizing hormones increase the PMF in intact cells. Thus, Ca2+ plays an important role in signal transduction from cytosol to mitochondria, with a single [Ca2+]m spike evoking a complex series of changes to activate mitochondrial oxidative metabolism.

Rapid Ca2+ refilling system of intracellular store(s) in human vascular endothelial cells

Channel adaptation is a basic property of the sarcoplasmic reticulum Ca2+-release channels/ryanodine receptors (RyRs). It allows channel activity to decay during sustained increases in the concentration of activating Ca2+. Despite the potential physiological importance of this self-confining process, its molecular mechanism is not well understood. To define the mechanism of adaptation we studied the dynamics of cardiac Ca2+-release channel (RyR) gating using the planar lipid bilayer technique in combination with photolysis of caged Ca2+ (DM-nitrophen). Channels activated by rapid and sustained increases in Ca2+ concentration (from 0.1 to 0.5 micromol/l) displayed three distinct gating modes, manifested as current records with frequent and long openings (H-mode), with rare and short openings (L-mode), and with no openings (I-mode). H-mode channel activity occurred primarily at early times while L- and I-modes predominated at late times after the rapid Ca2+ concentration increase. The decrease in probability of H-mode, mirrored by an increase in the probability of the I-mode, proceeded with a time constant similar to that observed for spontaneous decay in channel activity (i.e., adaptation) in ensemble average records. These results indicate that RyR adaptation transpires by a shift of channel gating from a high open probability mode to low open probability and inactivated modes of the channel.