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11.
Early after-depolarisations induced by noradrenaline may be initiated by calcium released from sarcoplasmic reticulum 总被引:1,自引:0,他引:1
We investigated the effect of 10–8 M noradrenaline (NA) on [Ca2+], and electrical activity of single myocytes of guinea-pig ventricular myocardium loaded with Indo 1-AM. Membrane potential was recorded by means of the patch electrode and patch amplifier set to the current clamp mode. Cells were stimulated at a rate of 30/min by 3 ms pulses of the current injected through the recording electrode. Superfusion of NA resulted in slight shortening of action potentials (APs), increase in rate of rise and amplitude of the respective Ca2+ transients, and appearance of secondary Ca2+ transients of two kinds: 1. appearing before repolarisation of AP and decay of the preceding Ca2+ transient were completed and 2. appearing between the APs. We named them early after-transients (EAT) and delayed after-transients (DAT), respectively. Without any additional intervention EATS caused some prolongation of APs duration and DATs resulted in subthreshold delayed after-depolarisations (DADS). When sarcolemmal K+ conductance was decreased by tetraethylammonium (TEA) in the patch electrode or 20 M BaCl2 in the Tyrode solution, EATs initiated early after depolarizations (EADs) and DATs initiated suprathreshold DADs triggering full-sized APs. Superfusion of 30.0 mM Na+ (replaced with LiCl) resulted in reduction of AP duration by -70% and appearance of DATs. Also, the frequent multiple oscillations of Ca 2+ concentration were often observed. Neither DATs nor the oscillations had any affect on electrical activity of the cells. Their electrogenicity could not be increased by TEA or 20.0 M Ba2+. EATs and DATs and their respective EADs and DADs could not be initiated by NA or low Na+ superfusion in the cells pretreated with 2 × 10–7 M thapsigargin, a selective blocker of Ca2+-ATPase of sarcoplasmic reticulum (SR). We conclude that in contrast to the current hypothesis, EADs can be initiated by Ca2+ released early in the cardiac cycle from the overloaded SR, and that electrogenicity of both types of Ca2+ oscillations critically depends on the sarcolemmal K+ conductance. 相似文献
12.
The effect of increased concentrations of calcium (Ca) (3–24 mM) and boron (B) (100–800 M) in the medium was studied on the occurrence of shoot tip necrosis (STN) in cultures of Pistacia vera L. STN was significantly reduced by application of Ca or B, however media with more than 200 M boron had reduced shoot multiplication. Ca (12–24 mM) supplied as calcium chloride reduced STN without any adverse effect on shoot multiplication or elongation, whereas calcium acetate reduced elongation. It is concluded that STN is a physiological mineral disorder associated with Ca and/or B deficiency in the meristematic regions of actively growing shoots. Application of Ca (up to 24 mM) as calcium chloride to the medium was the best treatment for the control of STN. Reduction of humidity or increased aeration in the culture jars did not have any significant effect on the occurrence of STN.Abbreviations MS
Murashige and Skoog medium
- STN
Shoot tip necrosis 相似文献
13.
The effects of lead on Ca2+ homeostasis in nerve terminals was studied. Incubation with leadin vitro stimulated the activity of calmodulin and the maximum effect was observed at 30 M lead, higher concentrations had an inhibitory effect.In vivo exposure to lead increased the activity of calmodulin by 45%. Lead had an inhibitory effect on Ca2+ ATPase activity in both calmodulin-rich and calmodulin-depleted synaptic plasma membranes, the IC50 values for inhibition being 13.34 and 16.69 M respectively. Exogenous addition of calmodulin (5 g) and glutathione (1 mM) to calmodulin rich synaptic plasma membranes reversed the inhibition by IC50 concentration of lead.In vivo exposure of lead also significantly reduced the Ca2+ ATPase activity, resulting in an increase in intrasynaptosomal calcium. Concomitant with the increase in intrasynaptosomal calcium, lipid peroxidation values also increased significantly in lead-treated animals. In addition lead also had an inhibitory effect on depolarization induced Ca2+ uptake and the inhibition was found to be a competitive one. The results sugest that lead exerts its toxic effects by modifications of the intracellular calcium messenger system which would have serious consequences on neuronal functioning. 相似文献
14.
Effect of shock-loading of heavy metals on total organic carbon and phosphate removal in an anaerobic-aerobic activated sludge process 总被引:1,自引:0,他引:1
The effect of shock-loading of zinc, copper and cadmium ions on the removal of total organic carbon (TOC) and phosphate in an anaerobic-aerobic activated sludge process was investigated. TOC removal was not sensitive to shock-loading of Zn2+ and Cd2+ ions, and complete removal was achieved even at 20 mg Zn2+/l and 20 mg Cd2+/l. However, with over 1 mg Cu2+/1 TOC removal efficiency decreased. PO
inf4
sup3-
removal, in contrast, was extremely sensitive to these metal ions, with the threshold being 1 mg Zn2+/l and 1 mg Cd2+/l. Higher concentrations adversely affected PO
inf4
sup3-
removal. Copper again proved detrimental; no PO
inf4
sup3-
removal was achieved even at 1 mg Cu/l. These results highlight the sensitivity of the removal efficiencies of TOC and PO
inf4
sup3-
to shock loadings of these heavy metals.Y.P. Ting is with the Department of Chemical Engineering, National University of Singapore, Kent Ridge, 0511, Singapore; H. Imai and S. Kinoshita are with the Department of Chemical Process Engineering, Hokkaido University, Sapporo 060, Japan. 相似文献
15.
We have previously shown that volatile anesthetics inhibit glutamate-stimulated [3H]MK-801 binding to the ionophore of NMDA receptor complexes in rat brain. In the present study, we examined the influence of enflurane and halothane on NMDA-stimulated45Ca uptake by a microvesicle fraction isolated from rat brain. NMDA stimulated45Ca uptake (30 sec) by rat brain microvesicles by up to 70% with an EC50 of 1.4±0.5 M. The NMDA-stimulated45Ca uptake was inhibited by MK-801 and D-AP-5 with IC50's of 10 M. Enflurane and halothane inhibited45Ca uptake stimulated by 100 M NMDA by as much as 60–80% with IC50's of 0.2–0.3 mM, concentrations achieved during routine clinical use. Basal45Ca uptake measured in the absence of agonist was not affected by the anesthetics. Glycine did not affect the level of NMDA-stimulated45Ca uptake, but markedly reduced the inhibition of uptake caused by enflurane and halothane. Preincubation of microvesicles with NMDA resulted in a desensitization of NMDA-stimulated45Ca uptake, with a t1/2 of 20 sec. Enflurane and halothane diminished both the extent and rate of development of this desensitization, as did glycine. These findings support the idea that volatile anesthetic interference with neurotransmission at NMDA receptor complexes contributes to the development of the anesthetic state. 相似文献
16.
Anthony P. Fordham-Skelton F. Safadi M. Golovkin A. S. N. Reddy 《Plant Molecular Biology Reporter》1994,12(4):358-366
Calmodulin labeled with125I or34S has been used to screen expression libraries to isolate cDNAs encoding calmodulin-binding proteins (CBPs) from several eukaryotic
systems. The use of radiolabeled calmodulin has, however, several disadvantages. We have developed a nonradiactive method
to isolate cDNAs for CBPs using biotinylated calmodulin. Screening of a cDNA library in an expression vector with biotinylated
calmodulin resulted in the isolation of cDNAs encoding CBPs. Avidin and biotin blocking steps, prior to incubation of the
filters with biotinylated calmodulin, are found to be essential to eliminate the cDNAs that code for biotin-containing polypeptides.
The cDNA clones isolated using this nonradioactive method bound calmodulin in a calcium-dependent manner. The binding of biotinylated
calmodulin to these clones was completely abolished by ethylene glycolbis(\-aminoethylether)-N,N′-tetraacetic acid (EGTA),
a calcium chelator. Furthermore, the isolated cDNAs were confirmed by probing the clones with35S-labeled calmodulin. All the isolated clones bound to radiolabeled calmodulin in the presence of calcium but not in the presence
of EGTA. The method described here is simple, fast, and does not involve preparation and handing of radiolabeled calmodulin.
All the materials used in this method are commercially available; hence, this procedure should be widely applicable to isolate
cDNAs encoding CBPs from any eukaryotic organism. 相似文献
17.
Stephen D. Bird Robert J. Walker Michael J. Hubbard 《In vitro cellular & developmental biology. Animal》1994,30(7):420-424
Summary The effect of a conventional antibiotic (penicillin/streptomycin) mixture on the widely used kidney epithelial cell line,
LLC-PK1, was investigated by measuring growth and intracellular free calcium. Free calcium concentration was the same in cells cultured
for 3 to 7 wk with (“plus”) and without (“minus”) antibiotics both at rest and when challenged with high (14 mM) external calcium. When exposed to vasopressin, minus cells exhibited significantly smaller calcium transients than plus
cells. A similar difference existed for transients elicited by a calcium ionophore, 4-br-A23187. After longer periods of culture
(>20 wk), minus cells grew slower than plus cells but on reaching confluence (minus cells took 1 day longer) the morphologies
and viabilities were indistinguishable. The finding that culture with penicillin/streptomycin reversibly modified some properties
of LLC-PK1 cells, at least partly through altered calcium homeostasis, is of importance for workers using this cell model to study drug
effects and raises the general possibility of similar effects on other cultured cells. 相似文献
18.
The purpose of this study was to make a prognosis of the effects of extended purification of terrestrial waste water, reaching the Wadden Sea by the River Rhine and Lake IJssel, on the phosphate concentration in the western Wadden Sea.The quantities of different phosphorus fractions in intertidal and subtidal sediments of the Marsdiep tidal basin (western Dutch Wadden Sea) were measured. Different methods are applied to determine the amount of phosphorus that can be released from these sediments. The direct bioavailability is determined by inoculating sediment suspensions with a natural mixture of precultured micro-organisms from the sampling area. A second approach is the measurement of the phosphate release under different redox conditions. Sequential extraction of sediment samples with different solvents is also applied. Under the present conditions and compared to the nutrient loads from fresh water (Lake IJssel) and from the North Sea, the phosphorus stored in the sediments of the western Dutch Wadden Sea plays a minor role in the total supply to micro-algae and bacteria. The bulk of the biologically available phosphorus in the sediments originates from the metal-associated fraction. Releasable phosphate may contribute to the local annual primary production to an extent of ca 45 to ca 150 g C m–2 a–1. The total amount of phosphorus in the sediment (mainly calcite associated) is twice to 6 times the biologically available amount. 相似文献
19.
Increased intracellular calcium concentration ([Ca2+]i) is required for smooth muscle contraction. In tracheal and other tonic smooth muscles, contraction and elevated [Ca2+]i are maintained as long as an agonist is present. To evaluate the physiological role of steady-state increases in Ca2+ on tension maintenance, [Ca2+]i was elevated using ionomycin, a Ca2+ ionophore or charybdotoxin, a large-conductance calcium-activated potassium channel (KCa) blocker prior to or during exposure of tracheal smooth muscle strips to Ach (10–9 to 10–4
M). Ionomycin (5 µM) in resting muscles induced increases in [Ca2+]i to 500±230 nM and small increases in force of 2.6±2.3 N/cm2. This tension is only 10% of the maximal tension induced by ACh. Charybdotoxin had no effect on [Ca2+]i or tension in resting muscle. After pretreatment of muscle with ionomycin, the concentration-response relationship for ACh-induced changes in tension shifted to the left (EC50=0.07±0.05 µM ionomycin; 0.17±0.07 µM, control, p<0.05). When applied to the muscles during steady-state responses to submaximal concentrations of ACh, both ionomycin and charybdotoxin induced further increases in tension. The same magnitude increase in tension occurs after ionomycin and charybdotoxin treatment, even though the increase in [Ca2+]i induced by charybdotoxin is much smaller than that induced by ionomycin. We conclude that the resting muscle is much less sensitive to elevation of [Ca2+]i when compared to muscles stimulated with ACh. Steady-state [Ca2+]i limits tension development induced by submaximal concentrations of ACh. The activity of KCa moderates the response of the muscle to ACh at concentrations less than 1 µM. 相似文献
20.
Blackfoot disease is a peripheral vascular disease resulting in gangrene of the lower extremities. Although extensive epidemiological
study has implicated high arsenic content in artesian well water of the endemic area bears some important connection with
the disease, the etiology of the disease is still not clarified. In this study, attention is paid to chemical speciation of
arsenic in order to find out whether the concentrations of arsenic species in urine of Blackfoot disease patients are different
from those of controls. Experimental results indicate that the total arsenic, inorganic arsenic, monomethylarsonic acid, and
other forms of arsenic in the urine of patients are significantly higher than those of the contols. The possible connection
of those arsenic species with the etiology of the disease is discussed. 相似文献