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1.
Wheat leaf growth is known to be spatially affected by salinity. The altered spatial distribution of leaf growth under saline
conditions may be associated with spatial changes in tissue mineral elements. The objective of this study was to evaluate
the spatial distributions of mineral elements and their net deposition rates in the elongating and mature zones of leaf 4
of the main stem of spring wheat (Triticum aestivum L. cv. Lona) during its linear growth phase under saline soil conditions. Plants were grown in an illitic-chloritic silty
loam with 0 and 120 mM NaCl. Three days after emergence of leaf 4, sampling was begun at 3 and 13 h into the 16-h light period.
Spatial distributions of fresh weight (FW), dry weight (DW), and Na+, K+, Cl−, NO−
3, Ca2+, Mg2+, total P, and total N in the elongating and mature tissues were determined on a millimeter scale. The patterns of spatial
distribution of Na+, Cl−, K+, NO3
−, and Ca2+ in the growing leaves were affected by salinity, while those of Mg2+, total P, and total N were not. Sodium, K+, Cl−, Ca2+, Mg2+, and total N concentrations (mmol · kg−1 FW) were consistently higher at 120 mM NaCl than at 0 mM NaCl along the leaf axis from the leaf base, whereas NO3
− concentration was lower at 120 mM NaCl. Deposition rates of all nutrients were greatest in the elongation zone. The elongation
zone was the strongest sink for mineral elements in the leaf tissues. Local net deposition rates of Na+, Cl−, Ca2+, and Mg2+ (mmol · kg−1 FW · h−1) in the most actively elongating zone were enhanced by 120 mM NaCl, whereas for NO3
− this was depressed. The lower supply of NO−
3 to growing leaves may be responsible for the inhibition of growth under saline conditions. Higher tissue concentrations of
Na+ and Cl− may cause ion imbalance but probably did not result in ion toxicity in the growing leaves. Potassium, Ca2+, Mg2+, total P, and total N are less plausibly responsible for the reduction in leaf growth in this study. Higher tissue K+ and Ca2+ concentrations at 120 mM NaCl are probably due to the presence of high Ca2+ in the soil of this study.
Received: 13 March 1997 / Accepted: 9 June 1997 相似文献
2.
Hans Gesser William R. Driedzic Francisco Tadeu Rantin José Carlos de Freitas 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(7):474-480
Isometric force development of electrically paced preparations isolated from the systemic heart of Octopus vulgaris were utilized to examine the regulation of contractility by Ca2+. Increases in extracellular Ca2+, to the physiological level, resulted in enhancement of twitch force. For instance, at 36 beats · min−1 an increase in Ca2+ from 3 to 9 mmol · l−1 resulted in a threefold increase in twitch force development. When steady-state contraction at 12 beats · min−1 was followed by a rest period of either 5 or 10 min, the first contraction always exhibited either an increase in twitch
force or stayed unchanged such that post-rest twitch force was about 133% of the last value in the steady-state train. Ryanodine
(12.5 μmol · l−1), which is considered to be a specific inhibitor of the Ca2+ storage and release capabilities of the sarcoplasmic reticulum (SR), was applied to further assess Ca2+ handling. Twitch force fell to about 22% of the preteatment level in preparations paced at either 12 or 36 beats · min−1. In all preparations the frequency transition from 12 to 36 beats · min−1 was associated with an increase in resting tension. The␣increase␣was 37 ± 14% prior to ryanodine treatment and was significantly
elevated to 127 ± 33% following treatment. When steady-state contraction at 36 beats · min−1 was followed by a rest period of 10 s, the first contraction was not significantly different from the last beat in the train
prior to ryanodine; however, with ryanodine treatment, post-rest twitch force development significantly decreased. Twitch
force development was regular at pacing rates of up to 300 beats · min−1. Twitch force was maintained up to rates of 84 beats · min−1 but␣decreased thereafter and reached a value of about 10% at 300 beats · min−1. Resting tension increased substantially as frequency was elevated from 12 to 36 beats · min−1 and then gradually increased as frequency was further elevated to 180 beats · min−1. In conclusion, the Octopus ventricle is dependent upon extracellular Ca2+ for contraction. A post-rest potentiation of force development, the negative impact of ryanodine, and the ability to respond
regularly at high pacing rates imply a strong reliance on the SR in Ca2+ cycling based on criteria established for vertebrate hearts.
Accepted: 19 January 1997 相似文献
3.
Schröder B Vössing S Breves G 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(7):487-494
From various in vivo and in vitro studies it has been shown that the rumen represents a significant site of Ca2+ absorption in sheep and goats. It was the aim of the present study to further characterize the underlying mechanisms. Unidirectional
flux rates of Ca2+ across rumen wall epithelia of sheep were measured in vitro by applying the Ussing-chamber technique in the absence of electrochemical
gradients. Under these conditions, significant Ca2+ net flux rates (Jnet) clearly indicate the presence of active mechanisms for Ca2+ transport. Short chain fatty acids (SCFAs) caused highest stimulation of Ca2+ Jnet (6.3 ± 1.9 nmol · cm−2 · h−1) when used as a mixture of acetate, proprionate and butyrate in physiological proportions (36, 15, 9 mmol · l−1, respectively). The effect of 30 mmol · l−1 butyrate (3.2 ± 0.6 nmol · cm−2 · h−1) was higher than respective amounts of propionate and acetate (0.6 ± 0.8 nmol · cm−2 · h−1 and 0.9 ± 0.8 nmol · cm−2 · h−1, respectively). Eliminating SCFAs resulted in Ca2+ Jnet of 0.4 ± 1.1 nmol . cm−2 . h−1. Addition of Ca channel blocker verapamil (mucosal 1 mmol · l−1) had no significant effect on SCFA-stimulated Jnet of Ca2+, whereas application of Na+/H+ inhibitor amiloride (mucosal 1 mmol · l−1) further enhanced the Ca2+ Jnet by >65%. The Ca2+-pump inhibitor vanadate had no significant effect on Jnet of Ca2+. Dietary Ca depletion enhanced calcitriol plasma concentrations but had no effect on active Ca2+ absorption across the rumen wall of sheep. In addition, no effect on active Ca2+ absorption could be observed during early lactation. In conclusion, there is clear evidence for the rumen as a main site
for active Ca2+ absorption in sheep. Our results suggest the presence of a Ca2+/H+ exchange mechanism in the apical membrane of rumen epithelial cells which depends on SCFA absorption and which does not seem
to be under the control of calcitriol. Basolateral Ca2+ extrusion occurs independently from Ca2+-pump activity and may be accomplished via Na+/Ca2+ exchange.
Accepted: 29 June 1999 相似文献
4.
K+-conductive pathways were evaluated in isolated surface and crypt colonic cells, by measuring 86Rb efflux. In crypt cells, basal K+ efflux (rate constant: 0.24 ± 0.044 min−1, span: 24 ± 1.3%) was inhibited by 30 mM TEA and 5 mM Ba2+ in an additive way, suggesting the existence of two different conductive pathways. Basal efflux was insensitive to apamin,
iberiotoxin, charybdotoxin and clotrimazole. Ionomycin (5 μM) stimulated K+ efflux, increasing the rate constant to 0.65 ± 0.007 min−1 and the span to 83 ± 3.2%. Ionomycin-induced K+ efflux was inhibited by clotrimazole (IC50 of 25 ± 0.4 μM) and charybdotoxin (IC50 of 65 ± 5.0 nM) and was insensitive to TEA, Ba2+, apamin and iberiotoxin, suggesting that this conductive pathway is related to the Ca2+-activated intermediate-conductance K+ channels (IKca). Absence of extracellular Ca2+ did neither affect basal nor ionomycin-induced K+ efflux. However, intracellular Ca2+ depletion totally inhibited the ionomycin-induced K+ efflux, indicating that the activation of these K+ channels mainly depends on intracellular calcium liberation. K+ efflux was stimulated by intracellular Ca2+ with an EC50 of 1.1 ± 0.04 μM. In surface cells, K+ efflux (rate constant: 0.17 ± 0.027 min−1; span: 25 ± 3.4%) was insensitive to TEA and Ba2+. However, ionomycin induced K+ efflux with characteristics identical to that observed in crypt cells. In conclusion, both surface and crypt cells present
IKCa channels but only crypt cells have TEA- and Ba2+-sensitive conductive pathways, which would determine their participation in colonic K+ secretion. 相似文献
5.
Xue-Qin Xie Jie Wang Bao-Fu Huang Sheng-Hua Ying Ming-Guang Feng 《Applied microbiology and biotechnology》2010,86(5):1543-1553
A superoxide dismutase (SOD) was characterized from Beauveria bassiana, a fungal entomopathogen widely applied to insect control. This 209-aa enzyme (BbSod2) showed no more than 71% sequence identity
to other fungal Mn-SODs, sharing all conserved residues with the Mn-SOD family and lacking a mitochondrial signal. The SOD
activity of purified BbSod2 was significantly elevated by Mn2+, suppressed by Cu2+ and Zn2+ but inhibited by Fe3+. Overexpressing the enzyme in a BbSod2-absent B. bassiana strain enhanced its SOD activity (107.2 ± 6.1 U mg−1 protein) by 4–10-fold in different transformants analyzed. The best BbSod2-transformed strain with the SOD activity of 1,157.9 ± 74.7 U mg−1 was 93% and 61% more tolerant to superoxide-generating menadione in both colony growth (EC50 = 2.41 ± 0.03 versus 1.25 ± 0.01 mM) and conidial germination (EC50 = 0.89 ± 0.06 versus 0.55 ± 0.07 mM), and 23% more tolerant to UV-B irradiation (LD50 = 0.49 ± 0.02 versus 0.39 ± 0.01 J cm−2). Its virulence to Spodoptera litura larvae was enhanced by 26% [LT50 = 4.5 (4.2–4.8) versus 5.7 (5.2–6.4) days]. Our study highlights for the first time that the Mn2+-cofactored, cytosolic BbSod2 contributes significantly to the virulence and stress tolerance of B. bassiana and reveals possible means to improving field persistence and efficacy of a fungal formulation by manipulating the antioxidant
enzymes of a candidate strain. 相似文献
6.
Bernd Schröder Ina Rittmann Ernst Pfeffer Gerhard Breves 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):43-51
Unidirectional flux rates of Ca2+ across gastrointestinal tissues from sheep and goats were measured in vitro by applying the Ussing-chamber technique. Except for the sheep duodenum, mucosal to serosal Ca2+ flux rates (J
ms) exceeded respective flux rates in the opposite direction (J
sm) in both species and in all segments of the intestinal tract. This resulted in net Ca2+ flux rates␣(J
net = J
ms − J
sm) ranging between −2 and 9 nmol · cm−2 · h−1 in sheep and between 10 and 15 nmol cm−2 · h−1 in goats. In sheep, only J
net in jejunum, and in goats, J
netin duodenum and jejunum were significantly different from zero. Using sheep rumen wall epithelia, significant J
net of Ca2+ of around 5 nmol · cm−2 · h−1 could be detected. Since the experiments were carried out in the absence of an electrochemical gradient, significant net
Ca2+ absorption clearly indicates the presence of active mechanisms for Ca2+ transport. Dietary Ca depletion caused increased calcitriol plasma concentrations and induced significant stimulations of
net Ca2+ absorption in goat rumen. J
net of Ca2+ across goat rumen epithelia was significantly reduced by 1 mmol · l −1 verapamil in the mucosal buffer solution. In conclusion, there is clear evidence for the rumen as a main site for active
Ca2+ absorption in small ruminants. Stimulation of active Ca2+ absorption by increased plasma calcitriol levels and inhibition by mucosal verapamil suggest mechanistic and regulatory similarities
to active Ca2+ transport as described for the upper small intestines of monogastric species.
Accepted: 31 July 1996 相似文献
7.
Moni Brauer Wen-Jun Zhong Till Jelitto Christian Schobert Dale Sanders Ewald Komor 《Planta》1998,206(1):103-107
Changes in free Ca2+ in sieve-tube sap have been proposed to be important in the regulation of phloem transport, and Ca2+-activated protein kinase activity has been described in phloem exudate (S.A. Avdiushko et al. 1997 J Plant Physiol 150: 552–559).
Using atomic absorption spectrometry, we have determined that the total Ca2+ concentration in sieve-tube sap from Ricinus seedlings containing the endosperm is about 100 μM (range 80–150 μM). We used
three independent methods to determine the free calcium ion concentration in the phloem sap ([Ca2+]p). The first method was to calculate [Ca2+]p from the total Ca2+ concentration, in combination with the binding constants and concentrations of the ionic solutes in phloem sap. The resultant
estimate of [Ca2+]p was 63 μM. The second method used the Ca-specific fluorescent dye 2-[2-(5-carboxy)oxazole]-5-hydroxy-6-aminobenzofuran-N,N,O-triacetic-acid
(FURAPTRA) on exuded sieve-tube sap. Although the sap interfered severely with the fluorescence properties of the dye, Ca2+ titrations enabled a value of [Ca2+]p = 20 μM to be deduced. The third method used Ca2+-selective microelectrodes on exuded sap samples, which gave an average value for [Ca2+]p = 13 μM. No significant change in this value was observed during the sap exudation period. The Ca2+ buffer capacity was determined and the result of about 0.6 mmol · l−1 · pCa−1 displayed excellent agreement with the measured values of free and total Ca2+ concentration in sieve-tube sap. Since the measured values for free Ca2+ are 20- to 100-fold higher than those usually reported for the cytosol of a range of plant cells in resting conditions, it
is concluded that either regulation of [Ca2+]p is of limited physiological importance, or that the Ca2+-dependent proteins respond only to relatively high [Ca2+]p. The implications for regulation of cytosolic free Ca2+ in symplastically connected companion cells is discussed.
Received: 15 February 1998 / Accepted: 14 March 1998 相似文献
8.
Aldo Viarengo Graziella Mancinelli Bruno Burlando Isabella Panfoli Barbara Marchi 《Polar Biology》1999,21(6):369-375
Cell calcium is accumulated in intracellular stores by sarco-endoplasmic reticulum Ca2+ ATPases functionally interacting with the membrane lipid environment. Cold adaptations of membrane lipids in Antarctic Sea
organisms suggest possible adaptive effects also on sarco-endoplasmic reticulum Ca2+ ATPases. We investigated the SR Ca2+ ATPase of an Antarctic scallop, Adamussium colbecki, by characterising the enzyme activity and studying temperature effects. Ca2+ ATPase, assayed by following ATP hydrolysis, was thapsigargin- and vanadate-sensitive, showed maximum activity under 2 μM
Ca2+, 200 mM KCl and pH 7.2, and had a K
M for ATP of 22 ± 7 μM. Temperature effects showed an Arrhenius inversion between −1.8 and 0°C, indicating cold adaptation,
an Arrhenius break at 10°C, and a collapse above 20°C. A. colbecki accumulates high amounts of cadmium in the digestive gland; heavy metal effects on sarco-endoplasmic reticulum Ca2+ ATPases were therefore tested, finding an IC50 = 0.9 μM for Hg2+ and 3 μM for Cd2+. Finally, SDS-PAGE analysis showed a main band at about 100 kDa, which was identified as sarco-endoplasmic reticulum Ca2+ ATPase after trypsin digestion, and accounted for 60% total protein.
Accepted: 10 December 1998 相似文献
9.
S. M. E. Guirguis J. C. Yee D. F. Stiffler 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(5):328-334
The skin of intact, free-swimming Xenopus laevis transports Ca2+ inwardly in a manner that is proportional to the external [Ca2+] up to about 0.3 mmol · l−1, saturates above 0.3 mmol · l−1, and is opposed to the electrochemical gradient. Efflux is relatively constant at external concentrations between 0.016 and
0.6 mmol · l−1; net flux which is negative below 0.125 mmol · l−1 becomes positive above this external [Ca2+]. Allometric analysis suggests that both Ca2+ influx and efflux scale to the 2/3 power approximately like surface area. There were no significant differences in influx
between summer and fall animals; however, efflux was greater in the fall and this resulted in a change from positive balance
in the summer to negative balance in the fall. Isolated skins were shown to support a Ca2+ uptake rate of nearly 30 nmol · cm−2 · h−1. The phenylalkylamine verapamil in the apical bathing solution significantly inhibited this at 25 μmol · l−1. The benzothiazepine diltiazem was also effective at 50 μmol · l−1 while the dihydropyradine nifedipine was ineffective up to 100 μmol · l−1. The inorganic ion La3+ was effective at blocking Ca2+ uptake at 300 μmol · l−1; Ni2+ was also effective at 500 μmol · l−1 but Co2+ was ineffective up to 500 μmol · l−1. These results suggest that apical calcium channels in Xenopuslaevis skin have properties similar to mammalian L-channels and fish gill Ca2+ channels.
Accepted: 23 January 1997 相似文献
10.
Willem Bintig Judith Baumgart Wilhelm J. Walter Alexander Heisterkamp Holger Lubatschowski Anaclet Ngezahayo 《Journal of bioenergetics and biomembranes》2009,41(1):85-94
Purinergic signalling in rat GFSHR-17 granulosa cells was characterised by Ca2+-imaging and perforated patch-clamp. We observed a resting intracellular Ca2+-concentration ([Ca2+]i) of 100 nM and a membrane potential of −40 mV. This was consistent with high K+− and Cl− permeability and a high intracellular Cl− concentration of 40 mM. Application of ATP for 5–15 s every 3 min induced repeated [Ca2+]i increases and a 30 mV hyperpolarization. The phospholipase C inhibitor U73122 or the IP3-receptor antagonist 2-aminoethoethyl diphenyl borate suppressed ATP responses. Further biochemical and pharmacological experiments
revealed that ATP responses were related to stimulation of P2Y2 and P2Y4 receptors and that the [Ca2+]i increase was a prerequisite for hyperpolarization. Inhibitors of Ca2+-activated channels or K+ channels did not affect the ATP-evoked responses. Conversely, inhibitors of Cl− channels hyperpolarized cells to −70 mV and suppressed further ATP-evoked hyperpolarization. We propose that P2Y2 and P2Y4 receptors in granulosa cells modulate Cl− permeability by regulating Ca2+-release. 相似文献
11.
Aporn Bualuang Kanteera Soontharapirakkul Aran Incharoensakdi 《Journal of applied phycology》2010,22(2):123-129
The activity of Na+/H+ exchanger to remove toxic Na+ is important for growth of organisms under high salinity. In this study, the halotolerant cyanobacterium Aphanothece halophytica was shown to possess Na+/H+ exchange activity since exogenously added Na+ could dissipate a pre-formed pH gradient, and decrease extracellular pH. Kinetic analysis yielded apparent K
m (Na+) and V
max of 20.7 ± 3.1 mM and 3,333 ± 370 nmol H+ min−1 mg−1, respectively. For cells grown under salt-stress condition, the apparent K
m (Na+) and V
max was 18.3 ± 3.5 mM and 3,703 ± 350 nmol H+ min−1 mg−1, respectively. Three cations with decreasing efficiency namely Li+, Ca2+, and K+ were also able to dissipate pH gradient. Only marginal exchange activity was observed for Mg2+. The exchange activity was strongly inhibited by Na+-gradient dissipators, monensin, and sodium ionophore as well as by CCCP, a protonophore. A. halophytica showed high Na+/H+ exchange activity at neutral and alkaline pH up to pH 10. Cells grown at pH 7.6 under high salinity exhibited higher Na+/H+ exchange activity than those grown under low salinity during 15 days of growth suggesting a role of Na+/H+ exchanger for salt tolerance in A. halophytica. Cells grown at alkaline pH of 9.0 also exhibited a progressive increase of Na+/H+ exchange activity during 15 days of growth. 相似文献
12.
CYP102A1 is an efficient medium- to long-chain fatty acid hydroxylase that is able to accept a wide range of non-natural substrates
which bear no resemblance to the natural ones. 4-Hexylbenzoic acid (HBA) and 4-nonyloxybenzoic acid (NOBA) were identified
as CYP102A1 substrates via screening studies using the BD Oxygen Biosensor System. Spectroscopic binding studies showed that
these two substrates bind in the active site of CYP102A1 with K
d values of 2.6 ± 0.1 μM for HBA and 1.9 ± 0.2 μM for NOBA. NADPH consumption rates in the presence of HBA and NOBA were 45 ± 1 min−1 and 61 ± 1 min−1, respectively. The coupling efficiency for NADPH was 57% for NOBA, while it was 77% for HBA. During whole-cell biotransformations,
HBA was converted into ω−1- and ω−2-hydroxyhexylbenzoic acid, whereas NOBA was oxidized to ω−2-hydroxynonyloxybenzoic acid
and ω−2,ω−4-dihydroxynonyloxybenzoic acid. HBA was used as a fatty acid mimic to compare whole-cell biotransformations with
cell-free extracts. Whole-cell biotransformations carried out in a biphasic system resulted in 86% conversion of 5 mM HBA,
producing 3.8 mM ω−2- and 0.5 mM ω−1-hydroxyhexylbenzoic acid in 4 h with a turnover number of 4.1 min−1, whereas 100% conversion of 5 mM HBA was obtained in 1 h with crude cell extracts and a cofactor regeneration system, giving
a turnover number of 10.5 min−1. 相似文献
13.
T. C. Cox 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):344-350
Ion transport measured as short circuit current (Isc) across the skin of larval frogs is activated by amiloride, acetylcholine,
and ATP. In many epithelia, ATP stimulation of Isc involves an increase in intracellular calcium. To define the role of changes
in intracellular calcium in ATP stimulation of Isc in larval frog skin, epithelial cells were loaded with calcium by adding
5 μM ionomycin to a 2 mM calcium apical Ringer's solution. Calcium loading had no observable effect on baseline Isc or on
stimulation by ATP. Minimizing changes in intracellular calcium by loading the cell with the calcium chelator BAPTA also had
no measurable effect on ATP stimulation of Isc. When the apical side was bathed with Ca2+-free Ringer's solution, ionomycin increased Isc up to 15 μA. This increase was partially blocked by 2 mM Ca2+, 2 mM Mg2+, and 10 μM W-7. Other experiments showed that baseline-stimulated and ATP-stimulated Isc were always larger in 2 mM Mg2+ Ringer's compared to 2 mM Ca2+. In dissociated cells bathed in 2 mM Ca2+ Ringer's, ATP had no effect on intracellular calcium as measured by Fluo-LR fluorescence changes. In conclusion, ATP apparently
stimulates Isc without concomitant changes in intracellular calcium. This is consistent with a directly ligand-gated receptor
at the apical membrane with P2X-like characteristics.
Accepted: 21 April 1999 相似文献
14.
Production of hexanoic acid from d-galactitol by a newly isolated Clostridium sp. BS-1 总被引:1,自引:0,他引:1
Byoung Seung Jeon Byung-Chun Kim Youngsoon Um Byoung-In Sang 《Applied microbiology and biotechnology》2010,88(5):1161-1167
In a study screening anaerobic microbes utilizing d-galactitol as a fermentable carbon source, four bacterial strains were isolated from an enrichment culture producing H2, ethanol, butanol, acetic acid, butyric acid, and hexanoic acid. Among these isolates, strain BS-1 produced hexanoic acid
as a major metabolic product of anaerobic fermentation with d-galactitol. Strain BS-1 belonged to the genus Clostridium based on phylogenetic analysis using 16S rRNA gene sequences, and the most closely related strain was Clostridium sporosphaeroides DSM 1294T, with 94.4% 16S rRNA gene similarity. In batch cultures, Clostridium sp. BS-1 produced 550 ± 31 mL L−1 of H2, 0.36 ± 0.01 g L−1 of acetic acid, 0.44 ± 0.01 g L−1 of butyric acid, and 0.98 ± 0.03 g L−1 of hexanoic acid in a 4-day cultivation. The production of hexanoic acid increased to 1.22 and 1.73 g L−1 with the addition of 1.5 g L−1 of sodium acetate and 100 mM 2-(N-morpholino)ethanesulfonic acid (MES), respectively. Especially when 1.5 g L−1 of sodium acetate and 100 mM MES were added simultaneously, the production of hexanoic acid increased up to 2.99 g L−1. Without adding sodium acetate, 2.75 g L−1 of hexanoic acid production from d-galactitol was achieved using a coculture of Clostridium sp. BS-1 and one of the isolates, Clostridium sp. BS-7, in the presence of 100 mM MES. In addition, volatile fatty acid (VFA) production by Clostridium sp. BS-1 from d-galactitol and d-glucose was enhanced when a more reduced culture redox potential (CRP) was applied via addition of Na2S·9H2O. 相似文献
15.
Summary. The fungal toxin cytochalasin D as well as endogenous gelsolin depolymerize filamentous actin which may induce dynamic uncoupling
of membrane ion channels. In vitro application of cytochalasin D reduced NMDA-induced [3H]noradrenaline release from mouse brain neocortical slices by 38%. In gsn deficient neocortical synaptosomes [Ca2+]i increase in response to K+ (30 mM) depolarization was 33% higher than in wild-type. After transient focal cerebral ischemia K+-induced [Ca2+]i increase in neocortical synaptosomes was 56% lower than in synaptosomes prepared from the non-ischemic contralateral hemisphere.
After in vivo pretreatment with cytochalasin D 10 min before MCA occlusion K+-induced [Ca2+]i increase in synaptosomes in vitro prepared 1 h after reperfusion from the ischemic hemisphere was only 25% lower than in contralateral synaptosomes, while
cytochalasin D pretreatment in vivo did not reduce K+-induced [Ca2+]i increase in vitro. Hence, presynaptic Ca2+ influx and subsequently neuronal vulnerability are attenuated by increased and are aggravated by decreased F-actin depolymerization.
Received June 29, 2001 Accepted August 6, 2001 Published online August 9, 2002 相似文献
16.
Endothelin is one of the most potent vasoconstrictors known. It plays an important role in the regulation of vascular tone and in the development of many cardiovascular diseases. This study focuses on the receptor types and the Ca2+ mobilization responsible for endothelin-1 (ET-1) contraction in de-endothelialized pig coronary artery rings. ET-1 contracted the artery rings with an EC50 = 6.5 ± 1 nM and a maximum contraction which was 98.6 ± 9% of the contraction produced by 60 mM KCl. BQ123 (5 µM), an ETA antagonist, reversed 78 ± 3% of the ET-1 contraction (50 nM). IRL1620, a selective ETB agonist, produced 23 ± 3% of the total ET-1 contraction with an EC50 = 12.7 ± 2 nM. More than 85% of the contraction due to 100 nM IRL 1620 was inhibited by 200 nMBQ788, an ETB antagonist. Therefore, approximately 80% of the ET-1 contraction in this artery occurred via ETA receptors, and the other 20% was mediated by ETB receptors. To assess the Ca2+ pools utilized during the ET-1 response, ET-1 contraction was also examined in medium containing an L-type Ca2+ channel blocker nitrendipine, and in Ca2+ free medium containing 0.2 mM EGTA. In Ca2+ containing medium the contraction elicited by ET-1 was 98.6 ± 9% of the KCl contraction, however, in the presence 10 µM nitrendipine the ET-1 induced contraction was 54 ± 7% of the KCl contraction, and in Ca2+-free medium it was 13 ± 2%. Similarly, the IRL 1620 contractions in Ca2+ containing medium, in the presence of nitrendipine and in Ca2+-free medium were 22.4 ± 3%, 12 ± 3% and 11 ± 2% of the KCl response respectively. Thus, both ETA and ETB contractions utilize extracellular Ca2+ pools via L-type Ca2+ channels and other undefined route(s), as well as intracellular Ca2+ pools. In the pig coronary artery smooth muscle, ET-1 contractions occur predominantly via ETA receptors, with ETB receptors using similar Ca2+ mobilization pathways, but the ETB receptors appear to use the intracellular Ca2+ stores to a greater extent. 相似文献
17.
In caulonemal filaments of the moss, Physcomitrella patens, which had been incubated in darkness, 3 s irradiation with blue light (λmax 450 nm) at fluence rates of 100 μmol m−2 s−1 and above caused a transient␣increase in cytosolic calcium ion concentration, [Ca2+]cyt, which was both intensity- and time-dependent. Measurements of [Ca2+]cyt were made using moss transformed with the cDNA for apoaequorin and reconstituting the Ca2+-dependent photoprotein aequorin in the cytosol by incubation in coelenterazine.␣In response to blue light at fluence rates
of 100–1000 μmol photons m−2 s−1, [Ca2+]cyt increased transiently from a basal level of approximately 50 nM to between 200 and 700 nM. Irradiation with red light did
not evoke any measurable change in [Ca2+]cyt. The presence of calcium in the incubating medium was not required for the increase in [Ca2+]cyt to occur. A mutant strain, gad-139, was identified which required an irradiance of only 1 s to evoke a response. The kinetics showed a delay of approximately
6 s from the beginning of illumination before the beginning of the increase in [Ca2+]cyt. The data suggest that the activation of a photoreceptor rather than the direct opening of calcium channels is involved in
this blue-light response.
Received: 4 December 1997 / Accepted: 4 May 1998 相似文献
18.
Wadhwa DR Care AD 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2000,170(8):581-588
Net Ca2+ and Mg2+ absorption rates were measured in vivo from buffer solutions placed in the washed reticulo-rumen, isolated in situ in 30
conscious, trained sheep. An increase in concentration of short chain fatty acids (SCFA) in the buffer, over the range 0–50 mM,
was shown to stimulate the net rates of absorption of Ca2+ and Mg2+ ions from the rumen. Similarly, the results of in vitro experiments, carried out with ovine rumen epithelium mounted in short-circuited
Ussing chambers, showed that the absence of SCFA from the chamber fluid resulted in a reduction in Jnet Ca2+ caused by reduced flux of Ca2+ ions in the mucosal to serosal direction (Jms Ca2+). The addition of 1 mM acetazolamide, an inhibitor of carbonic anhydrase, to the ruminal buffer used in the in vivo experiments
led to significant reductions in the net absorption rates of Ca2+and Mg2+ ions in the presence of SCFA (50 mmol l−1) but not in the absence of SCFA. However, in the in vitro experiments, the addition of 60 μM ethoxyzolamide had no significant
effect on Jnet Ca2+. A reduction in pH of the intraruminal buffer in vivo from 6.8 to 5.4 led to significant increases in the net absorption
rates of Ca2+and Mg2+ ions, an effect which was duplicated for Ca2+ in preliminary in vitro experiments in which the pH of the mucosal buffer was reduced from 7.4 to 5.4. This stimulatory effect
was confined to Jms Ca2+ and Jnet Ca2+. Ussing chambers were also used to demonstrate that Jnet Ca2+ was reduced by a high transmural potential difference (PD), caused by voltage clamping, independently of the mucosal K+ concentration. Both unidirectional Ca2+ fluxes consisted of a PD-dependent and a K+-insensitive PD-independent component. The latter may be represented by a Ca2+/2H+ antiporter. It is postulated that SCFA, and to a lesser extent H2CO3, can stimulate Jms Ca2+ by activation of an apical Ca2+/2H+ antiporter through the provision of protons within the ruminal epithelial cell. A mild reduction in ruminal pH may also lead
to a similar stimulation of this putative electroneutral exchange.
Accepted: 26 July 2000 相似文献
19.
Marina Granado e Sá B. B. Baptista L. S. Farah V. P. Leite F. P. Zanotto 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》2010,180(3):313-321
Crustaceans present a very interesting model system to study the process of calcification and calcium (Ca2+) transport because of molting-related events and the deposition of CaCO3 in the new exoskeleton. Dilocarcinus pagei, a freshwater crab endemic to Brazil, was studied to understand Ca2+ transport in whole gill cells using a fluorescent probe. Cells were dissociated, all of the gill cell types were loaded with
fluo-3 and intracellular Ca2+ change was monitored by adding Ca as CaCl2 (0, 0.1, 0.25, 0.50, 1.0 and 5 mM), with a series of different inhibitors. For control gill cells, Ca2+ transport followed Michaelis–Menten kinetics with K
m = 0.42 ± 0.04 mM and V
max = 0.50 ± 0.02 μM (Ca2+ change × initial intracellular Ca−1 × 180 s−1; N = 14, r
2 = 0.99). Verapamil (a Ca2+ channel inhibitor) and amiloride (a Na+/Ca2+ exchanger [NCX] inhibitor) completely reduced intracellular Ca2+ transport, while nifedipine, another Ca2+ channel inhibitor, did not. Vanadate, a plasma membrane Ca2+-ATPase inhibitor (PMCA), increased intracellular Ca2+ in gill cells through a decrease in the efflux of Ca2+. Ouabain increased intracellular Ca2+, similar to the effect of KB-R, a specific NCX inhibitor for Ca2+ in the influx mode. Alterations in extracellular [Na] in the saline did not affect intracellular Ca2+ transport. Caffeine, responsible for inducing Ca release from sarcoplasmic reticulum in vertebrate muscle, increased intracellular
Ca2+ compared to control, suggesting an effect of this inhibitor in gill epithelial cells of Dilocarcinus pagei, probably through release of intracellular stores. We also demonstrate here that intracellular Ca2+ in gill cells of Dilocarcinus pagei was kept relatively constant in face of an extracellular Ca concentration of 50-fold, suggesting that crustaceans are able
to display Ca2+ homeostasis through various Ca2+ intracellular sequestration mechanisms and/or plasma membrane Ca2+ influx and outflux that are highly regulatory. In summary, studies using whole gill cells are an interesting approach for
working with real regulatory Ca2+ mechanisms in intact cells under physiological Ca levels (mM range), compared to earlier work using isolated vesicles of
various epithelial cells. 相似文献
20.
The ability to measure directly individual protoplast ion fluxes is a valuable addition to patch clamp and other techniques
when using protoplasts to study membrane transporters. Before interpreting observations on protoplasts in terms of behaviour
of intact cells and tissues, some methodological questions should be addressed. These include effects of space and time variations
of transporter activities over the membrane, the osmotic dependence of specific ion transporters and the effect of the regenerating
cell wall. In this study net H+ and Ca2+ fluxes were measured from individual corn (Zea mays L.) coleoptile protoplasts using a non-invasive microelectrode technique for ion flux measurements. For Ca2+, the flux distribution was almost symmetrical, ranging ±30 nmol · m−2 · s−1 around zero. For H+ it was skewed towards efflux ranging from −100 to +10 nmol · m−2 · s−1. The distribution of H+ fluxes through the protoplast surface was a complex mosaic which changed with time, sometimes showing oscillations. These
flux variations with time and position around the surface, apparently driven by endogenous mechanisms, may be relevant to
protoplast pH homeostasis. When the new cell wall was partially regenerated on the next day, the correlation between H+ and Ca2+ fluxes increased, which is consistent with the weak-acid Donnan-Manning model of cell wall ion exchange.
Received: 11 June 1997 / Accepted: 10 July 1997 相似文献