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1.
A specific fraction of immunoglobulin G binds to polymorphonuclear neutrophils and stimulates their phagocytic activity. This phagocytosis-stimulating activity resides solely in a small peptide termed tuftsin, of the sequence Thr-Lys-Pro-Arg, which has been isolated from the leukophilic immunoglobulin G fraction. The physiological significance of tuftsin has been demonstrated in splenectomized patients and patients with a congenital tuftsin abnormality, in whom the low levels of tuftsin in sera (measurable by radioimmunoassay) coincides with a high incidence of infection. Tuftsin has also been shown to enhance bactericidal activity in addition to phagocytosis. Its biological activities appear to be mediated via specific tuftsin receptors which have been found on macrophages, monocytes and granulocytes. In addition, tuftsin possesses chemotactic, migration-enhancing and mitogenic properties for leukocytes and has recently been shown to enhance their anti-tumor activity invitro as well as invivo. Other known activities of tuftsin include effects on the activity of the hexose monophosphate shunt, on the concentrations of intracellular cyclic nucleotides and on the efflux of Ca2+ in leukocytes. Tuftsin has been chemically synthesized in various laboratories using different procedures and also is available commercially. The above features of tuftsin plus the expected low toxicity of this peptide make tuftsin a very attractive agent for immunotherapy against infection and cancer. However, a great deal of caution needs to be exercised when using tuftsin due to inhibitory contaminants found in certain commercial preparations.  相似文献   

2.
Exposure of either alveolar macrophages or blood neutrophils to 0.2 – 1 μM ionophore A23187 in the presence of 0.1 – 1 mM CaCl2 causes a rapid extracellular release of Ca2+, which can be measured by a Ca2+-selective electrode. The initial rate at which the cation is extruded from the cells is about 0.1 – 0.2 μg-ions/min/ml of cell water. ATP depletion, but not replacement of extracellular Na+ with choline, produces a marked inhibition of Ca2+ release from macrophages. When the movements of Ca2+ between neutrophils and the incubation medium are followed by an isotopic technique, a transient increase in cell-associated 45Ca2+ is detected a few seconds after the addition of the ionophore. We suggest that the ionophore A23187 mobilises Ca2+ from intracellular stores, with a subsequent cell extrusion of the bivalent cation catalysed by a pump localised at the cell surface. These and other data are consistent with the conclusion that the peripheral Ca2+ pump system of macrophages and neutrophils is very similar to the well know Ca2+ pump of the red cells with regard to mechanism and capacity.  相似文献   

3.
Staphylococcal serine proteinase (SSP) can influence various functions of human polymorphonuclear leukocytes (PMNL) including chemotaxis and phagocytosis. Since the rise in intracellular free calcium concentration is an important step in signal transduction leading to phagocyte activation, we tested the ability of SSP to increase the intracellular free calcium concentration in human PMNL using the fluorescent calcium indicator Fura-2AM. PMNL isolated from healthy donors responded to SSP in the concentration range of 10 to 100 µg/ml. The highest Ca2+ rise (104 ± 47 nM) was observed for 10 µg/ml SSP. It was mainly dependent (81 ± 11%) on extracellular calcium influx, however, SSP mobilized 68 ± 7% of Ca2+ from intracellular calcium stores. Boiling of SSP or preincubation with phenylmethylsulphonylfluoride (an serine proteinase inhibitor) did not change its ability to increase intracellular free calcium concentration in PMNL. It suggests that active center of SSP is not responsible for Ca2+ mobilization. Finally, PMNL responded to each of three consecutive stimulations with SSP independently of the presence of high or low extracellular Ca2 concentration. This may be an additional mechanism responsible for activation of human PMNL and degradation of alveolar walls during the staphylococcal infection in the lower airways.  相似文献   

4.
A mitochondria-free membrane fraction prepared from rat myometrium accumulated 45Ca2+ in the presence of oxalic acid and ATP. The rate of transport of Ca2+ into the membranous vesicles was increased by greater than 50% in the presence of 3′,5′-cyclic AMP, but not by 2′,3′-cyclic AMP or 5′-AMP. Membrane ATPase activity was stimulated by cyclic AMP in a manner similar to Ca2+-transport. ATPase activity was stimulated by Mg2+; slight additional stimulation was obtained in the presence of Na+ and K+ but not in the presence of Ca2+. Despite the cyclic AMP sensitivity of membrane ATPase activity, the absence of any effect of inhibitors of Ca2+-transport suggest it has little to do with Ca2+ accumulation by the membranes.Cyclic AMP-induced increase in Ca2+-transport and membrane ATPase activity was duplicated in vivo by incubating uteri in 10−4 M isoproterenol prior to membrane isolation. Isoproterenol has been previously shown to increase myometrial cyclic AMP levels, and changes in Ca2+-transport by cell membranes in relation to intracellular cyclic AMP levels may be the mechanism through which hormones modulate uterine contractility.  相似文献   

5.
Summary Thyrotropin releasing hormone (TRH) acutely stimulates release of thyrotropin (TSH) and prolactin from anterior pituitary cells. A considerable number of studies have been performed with neoplastic and nonneoplastic pituitary cells in culture to elucidate the sequence of intracellular events involved in this action. Although cyclic AMP was suggested as an intracellular messenger, it has been demonstrated that TRH stimulation of hormone release can be dissociated from changes in cyclic AMP concentration, thereby supporting the contention that cyclic AMP is not a required mediator. In contrast, stimulation of hormone release by TRH requires Ca2+ and it seems likely that Ca2+ is the intracellular coupling factor between TRH stimulation and hormone secretion. TRH has been shown to stimulate 45Ca2+ efflux from preloaded pituitary cells. Enhanced 45Ca2+ efflux is thought to reflect an increase in the free intracellular Ca2+ concentration which leads to hormone release; however, the source of this Ca2– is uncertain. Results are reviewed from a series of experiments in pituitary cells which attempt to determine the pool (or pools) of Ca2+ that is affected by TRH. These include the following: the effects of decreasing the extracellular Ca2– concentration on hormone release stimulated by TRH; the effect of TRH on cellular Ca2+ as monitored by chlortetracycline; the effects of TRH on Ca2+ influx; the effects of the organic Ca2+ channel blocking agents, verapamil and methoxyverapamil, on TRH-stimulated hormone release; and the effects of TRH on plasma membrane potential difference and on Ca2+-dependent action potentials. Based on these data, separate hypotheses of the early events in TRH stimulation of hormone release in mammotropes and thyrotropes are proposed. In mammotropes, TRH is thought to stimulate prolactin release optimally by elevating the free intracellular Cat+ concentration by mobilizing cellular Ca2– only. In contrast, in thyrotropes under normal physiological conditions, TRH is thought to stimulate TSH release by mobilizing Ca2 from a cellular pool (or pools) and to augment this effect by also inducing influx of extracellular Ca2+ through voltage-dependent channels in the plasma membrane.  相似文献   

6.
Intact human neutrophils produced superoxide (O2 ) by the stimulation with N-formyl-methionyl-leucyl-phenylalanine (fMLP) even when the extracellular Ca2+ was absent (0.56±0.13 nmol/min per 106 cells). The production by fMLP was enhanced more than twice in the presence of the extracellular Ca2+. Moreover, the O2 production by fMLP in the presence of extracellular Ca2+ was enhanced nearly three times by the treatment of cells with H-89, an inhibitor of cyclic AMP-dependent protein kinase (PKA). The enhancement was not observed when the extracellular Ca2+ was depleted from the reaction mixture. In addition, H-89 did not enhance fMLP-induced O2 production of electropermeabilized neutrophils in which the intracellular Ca2+ concentration was fixed to about 100 nM. These observations suggest that not only Ca2+ influx but the inhibition of PKA is necessary for the maximum O2 production by fMLP and that the O2 production is partially suppressed by the activation of PKA induced by fMLP.  相似文献   

7.
Effects of N-formyl chemotactic peptides on the Ca2+ influx and efflux were investigated in guinea-pig peritoneal macrophages using an isotope tracer. fMet-Leu-Phe did not enhance the influx of 45Ca2+ into macrophages, whereas it stimulated the efflux of 45Ca2+ from macrophages at concentrations ranging from 10−10 M to 10−7 M. fMet-Met-Met and fMet-Leu also stimulated the 45Ca2+ efflux, albeit at much higher concentrations, while there was no stimulation with fMet. The mitochondrial inhibitors, oligomycin and NaN3, did not modify the 45Ca2+ efflux induced by the chemoattractants, yet they did induce the release of 45Ca2+ from the mitochondria. On the other hand, higher concentrations of the calmodulin antagonists, chlorpromazine and trifluoperazine, induced the release of 45Ca2+ from the NaN3-insensitive Ca2+ store site and mimicked the enhancement of the 45Ca2+ efflux by N-formyl chemotactic peptides. Thus, N-formyl chemotactic peptides appear to increase the levels of intracellular free Ca2+ in guinea-pig peritoneal macrophages, probably by inducing the release of Ca2+ from the NaN3-insensitive Ca2+ store site.  相似文献   

8.
A boron-containing antibiotic, boromycin (BM), was found to influence the Ca2+ homeostasis in both excitable and non-excitable cells. In non-excitable cells (human erythrocytes and leucocytes) it inhibited the resting passive45Ca2+ transport in 10–6–10–5 mol/L concentrations. In human erythrocytes, the passive 45Ca2+ transport induced by the presence of 1 mmol/L NaVO3 was inhibited by boromycin (90% inhibition) as well. The inhibitory effect of BM on the NaVO3-induced passive 45Ca2+ transport was diminished in the presence of inhibitory concentrations of nifedipine (10 mol/L – 60% inhibition) or of those of K+ o (75 mmol/L – 20% inhibition). On the other hand, in rat brain synaptosomes, and rat cardiomyocytes, BM stimulated the passive 45Ca2+ transport in resting cells at similar concentrations. In rat cardiomyocytes the stimulation was transient. The stimulatory effect on the passive 45Ca2+ transport in rat brain synaptosomes was accompanied with the increase of cytoplasmic Ca2+ concentration measured by means of the entrapped fluorescent Ca2+ chelator fura-2. The stimulatory effect of BM was diminished when synaptosomes were pre-treated with veratridine (10 mol/L) which itself stimulated the passive 45Ca2+ transport. At saturating concentrations of veratridine, no stimulatory effect of BM was observed. These results could be explained by the indirect interaction of BM with both Ca2+ and Na+ transport systems via transmembrane ionic gradients of monovalent cations and could be useful in determining whether the cells belong to excitable, or non-excitable cells.  相似文献   

9.
The effect of adrenocorticotropic hormone and dibutyryl cyclic AMP on the uptake of45Ca2+ by the rat adrenal gland has been investigated. After injection of 45Ca2+ and adrenocorticotropic hormone into rats, the adrenal 45Ca2+ concentration was significantly enhanced 90 to 180 min following hormone administration. The rise in adrenal 45Ca2+ content was accompanied by a marked increase of the serum corticosterone levels. During incubation of rat adrenal glands in the presence of 45Ca2+, adrenocorticotropic hormone and dibutyryl cyclic AMP caused significant accumulation of adrenal 45Ca2+ and increased corticosterone synthesis. The degree of stimulation of both adrenal 45Ca2+ uptake and corticosterone synthesis by adrenocorticotropic hormone or dibutyryl cyclic AMP was dependent upon the concentration of calcium in the incubation medium and upon the amount of adrenocorticotropic hormone or dibutyryl cyclic AMP added. Theophylline mimicked the stimulatory effect of adrenocorticotropic hormone and dibutyryl cyclic AMP and increased the uptake of 45Ca2+ by rat adrenal glands in vitro. Determination of calcium by atomic absorption spectroscopy showed that the adrenocorticotropic hormone-mediated adrenal 45Ca2+ uptake was due to a net accumulation of calcium in the tissue and not only to an increased rate of exchange of extracellular 45Ca2+ with the intracellular calcium pool. Adrenocorticotropic hormone-stimulated adrenal 45Ca2+ uptake was not observed when steroidogenesis was inhibited with elipten. Both adrenocorticotropic hormone-mediated corticosterone synthesis and adrenal 45Ca2+ uptake were abolished after treatment of rats with cycloheximide but not after treatment with actinomycin D, indicating that adrenal 45Ca2+ uptake and steroidogenesis have similar requirements for de novo protein synthesis, but not RNA synthesis.  相似文献   

10.
The effect of adrenocorticotropic hormone and dibutyryl cyclic AMP on the uptake of 45Ca2+ by the rat adrenal gland has been investigated. After injection of 45Ca2+ and adrenocorticotropic hormone into rats, the adrenal 45Ca2+ concentration was significantly enhanced 90 to 180 min following hormone administration. The rise in adrenal 45Ca2+ content was accompanied by a marked increase of the serum corticosterone levels. During incubation of rat adrenal glands in the presence of 45Ca2+, adrenocorticotropic hormone and dibutyryl cyclic AMP caused significant accumulation of adrenal 45Ca2+ and increased corticosterone synthesis. The degree of stimulation of both adrenal 45Ca2+ uptake and corticosterone synthesis by adrenocorticotropic hormone or dibutyryl cyclic AMP was dependent upon the concentration of calcium in the incubation medium and upon the amount of adrenocorticotropic hormone or dibutyryl cyclic AMP added. Theophylline mimicked the stimulatory effect of adrenocorticotropic hormone and dibutyryl cyclic AMP and increased the uptake of 45Ca2+ by rat adrenal glands in vitro. Determination of calcium by atomic absorption spectroscopy showed that the adrenocorticotropic hormone-mediated adrenal 45Ca2+ uptake was due to a net accumulation of calcium in the tissue and not only to an increased rate of exchange of extracellular 45Ca2+ with the intracellular calcium pool. Adrenocorticotropic hormone-stimulated adrenal 45Ca2+ uptake was not observed when steroidogenesis was inhibited with elipten. Both adrenocorticotropic hormone-mediated corticosterone synthesis and adrenal 45Ca2+ uptake were abolished after treatment of rats with cycloheximide but not after treatment with actinomycin D, indicating that adrenal 45Ca2+ uptake and steroidogenesis have similar requirements for de novo protein synthesis, but not RNA synthesis.  相似文献   

11.
The experiments were conducted on intracellularly persfused neurons of the molluskHelix pomatia, in which a serotonin (5-HT)-induced increase in the calcium current (ICa), mediated by cAMP, is observed. It was established that desensitization of the cell to the action of 5-HT is due to an increase in the intracellular Ca2+ concentration ([Ca2+]i). At [Ca2+]i=10–7 and 10–6 M, the effect of 5-HT constituted 60 and 32% of this value in the control (in the presence of 10 mM EGTA in the intracellular solution), respectively; at [Ca2+]i=10–5 M, there was no effect of 5-HT at all. The addition of the calmodulin antagonist trifluoperazine (5·10–5 mM) or blockers of phosphodiesterase (5 mM theophylline or 10–4 M IBMX) to the perfusate sharply weakened the ability of calcium to inhibit the effect of 5-HT; at [Ca2+]i=10–5 M, in the presence of one of these compounds, the effect constituted 60–70% of its control value. It is concluded that the calcium-calmodulin-dependent phosphodiesterase is a key link in the interaction of the two-signal transduction pathway — Ca2+ and cAMP in modulation of the calcium-channel activity.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 3, pp. 306–313, May–June, 1991.  相似文献   

12.
Cells were subjected to a range of 45Ca2+ influx loads with A23187. We measured cell 45Ca2+ with time and A23187 dose, and the apparent 45Ca2+ influxes (≡“J(in,app)”) at Ca2+ steady state. We also measured endogeneous exchangeable and total cell Ca2+, which were 50 and 17–220 μM respectively. The effects of A23187 and Ca2+ on cell ATP, swelling, net Cl permeability, and cell morphology were measured. These were modest and do not affect our conclusions.J(in,app) 3 × 10−4 [A23187]2.9·[Ca2+(o)]μmoles/l·min with 92–552 μM [Ca2+(o)] (≡ external Ca2+ concentration) and 0–7 μM A23187. J(in,app) was increased an order of magnitude by vanadate and is probably much less than the true influx. The least unlikely explanation found for the high [A23187] exponent, 2.9, was that most of the Ca2+ crossing the membrane is expelled by the pump before it can move deeper into the cell.Calcium pumping increased rapidly in response to increased influx, but the steady state cell 45Ca2+ was approximately proportional to J(in,app) rather than approximately constant between 10 and 120 μmoles/l·min with 184 μM [Ca2+(o)]. This is not the result expected from a simple feedback mechanism.At high A23187 doses the pump appears fully activated resulting in a linear relation between cell/medium 45Ca2+ and [A23187]−2. From the plot we calculated α≡free/total exchangeable Ca2+ = 0.38 ± 0.08 (n = 3) and a maximum pump rate, “Pmax” = 78 μmole/l·min. Pmax is underestimated insofar as J(in,app) is less than the true influx.  相似文献   

13.
Summary The localization and basic properties of Ca2+-accumulating sites in crayfish photoreceptors were studied with a novel preparation of peeled retinula cells in suspension. Peeled photoreceptors were obtained by gentle mechanical disruption of the retina, and incubated in media based on a Ca2+-EGTA buffer with ATP and oxalate. Electron microscopy of photoreceptors so treated showed the appearance of peculiar dense deposits inside vesicles of smooth endoplasmic reticulum (SER). EGTA-extraction and energy-dispersive X-ray microanalysis identified Ca as a major constituent of such deposits.45Ca2+ uptake experiments with peeled photoreceptors or with the crude particulate fraction of retinal homogenates revealed a rapid binding of radioactivity over the first 8 min, followed by a slower continued accumulation, which did not occur in the absence of ATP.45Ca2+ uptake is stimulated by an increase in the concentration of free Ca over the range 4×10–7 to 5×10–6 M, and becomes inhibited at higher levels.45Ca2+ uptake is depressed when K+ is replaced by Na+ or Li+ as the main monovalent cation in the medium, but it is not affected by illumination nor by the presence of caffeine or ruthenium red. These findings attest that the SER has a Na+-sensitive capacity for regulating the intracellular concentration of Ca2+ in these photoreceptors, and support the hypothesis of its probable role in the control of pigment granule transport and other structural changes involved in light/dark adaptation.  相似文献   

14.
Regulation of calcium handling by rat parotid acinar cells   总被引:1,自引:1,他引:0  
Summary Salivary gland fluid secretion following neurotransmitter stimulation is Ca2+-dependent. We have studied the control of cellular Ca2+ following secretory stimuli in rat parotid gland acinar cells. After muscarinic-cholinergic receptor activation, cytosolic Ca2+ is elevated 4–5 fold, due to both intracellular Ca2+ pool mobilization and extracellular Ca2+ entry. Fluid movement ensues due to the Ca2+-activated enhancement of membrane permeability to K+ and Cl. Basal cytosolic Ca2+ levels are tightly controlled at 150–200 nM through the action of high affinity and high capacity ATP-dependent Ca2+ transporters in the basolateral and endoplasmic reticulum membranes. Activity of these Ca2+ transporters can be modulated to facilitate rapid responsiveness and a sustained fluid secretory response necessary for alimentary function.  相似文献   

15.
Summary Calcium efflux was measured in desheathed rabbit vagus nerves loaded with45Ca2+. The effects of extracellular calcium, sodium, phosphate, potassium and lanthanum ions on the calcium efflux were investigated and the distribution of intracellular calcium determined by kinetic analysis of45Ca2+ efflux profiles. The45Ca2+ desaturation curve can be adequately described by three exponential terms. The rate constant of the first component (0.2 min–1) corresponds to an efflux from an extracellular compartment. The two slow components had rate constants of 0.03 and 0.08 min–1 and represent the efflux from two intracellular pools. The amounts of exchangeable calcium in these two pools, after a loading period of 150 min, were 0.170 and 0.102 mmol/kg wet weight, respectively. The total calcium efflux in physiological conditions amounted to about 24 fmol cm–2 sec–1. The magnitude of the two intracellular compartments as well as the total calcium efflux were markedly affected by extracellular phosphate, sodium and lanthanum, whereas the corresponding rate constants remained almost unchanged. Phosphate reversed the effect of sodium withdrawal on the calcium efflux: in the absence of phosphate, sodium withdrawal increased the calcium efflux to 224%, but in the presence of phosphate, sodium withdrawal decreased calcium efflux to 44%. Phosphate also affected the increase in calcium efflux produced by inhibitors of mitochondrial calcium uptake, suggesting that two different mitochondrial pools contribute to the control and regulation of intracellular calcium and of the transmembrane calcium transport.Deceased 18 April 1988  相似文献   

16.
The effects of guanine nucleotides and protein kinase C on prolactin-stimulated Ca2+ release from intracellular stores of pig oocytes were studied using the fluorescent dye chlorotetracycline. The effect of prolactin was related to the protein kinase C activation. Inhibition of protein kinase C stimulated Ca2+ release from intracellular stores of the pig oocytes treated with 5 ng/ml prolactin in the presence of extracellular Ca2+ and inhibited Ca2+ release from intracellular stores of the pig oocytes treated with 50 ng/ml prolactin. In a Ca2+-free medium, prolactin did not stimulate Ca2+ release from intracellular stores of the oocytes treated with GDP in the presence of GDP. GTP inhibition of protein kinase C activated Ca2+ release from intracellular stores of the pig oocytes treated with 5 ng/ml prolactin and inhibited Ca2+ release from intracellular stores of the pig oocytes treated with 50 ng/ml prolactin. These data suggest the influence of guanine nucleotides and protein kinase C on calcium metabolism, stimulated by prolactin.__________Translated from Ontogenez, Vol. 36, No. 3, 2005, pp. 199–204.Original Russian Text Copyright © 2005 by Denisenko, Kuzmina.  相似文献   

17.
The main aim of this study was to assess the kinetics of intracellular free calcium (Ca2+ i) handling by isolated rat hearts rendered ischemic for 30 min followed by 30 min of reperfusion analyzing the upstroke and downslope of the Ca2+ i transient. Changes in mechanical performance and degradation of membrane phospholipids – estimated by tissue arachidonic acid content – were correlated with Ca2+ i levels of the heart. The fluorescence ratio technique was applied to estimate Ca2+ i. The disappearance of mechanical activity of the heart preceded that of the Ca2+ i transient in the first 2 min of ischemia. The slope of upstroke of the Ca2+ i transient, reflecting Ca2+ release, decreased by 60%, while the duration of the downslope of the transient, reflecting Ca2+ sequestration, expressed a significant prolongation (105 ± 17 vs. 149 ± 39 msec) during the first 3 min of ischemia. At about 20 min of ischemia end-diastolic pressure expressed a 3.5-fold increase (contracture) when the fluorescence ratio showed a 2-fold elevation. Reperfusion was accompanied with a further precipitous increase in end-diastolic pressure, while resting Ca2+ i remained at end-ischemic levels. Increases in the arachidonic acid (AA) content of the ischemic and postischemic hearts were proportional to Ca2+ i levels. In summary, the present findings indicate that both calcium release and removal are hampered during the early phase of ischemia. Moreover, a critical level of Ca2+ i and a critical duration of ischemia may exist to provoke contracture of the heart. Upon reperfusion the hearts show membrane phospholipid degradation and signs of stunning exemplified by elevated AA levels, partial recovery of Ca2+ i handling and sustained depression of mechanical performance.  相似文献   

18.
We examine how collagen substrate topography, free intracellular calcium ion concentration ([Ca2+]i, and the association of gelsolin with nonmuscle myosin IIA (NMMIIA) at collagen adhesions are regulated to enable collagen phagocytosis. Fibroblasts plated on planar, collagen-coated substrates show minimal increase of [Ca2+]i, minimal colocalization of gelsolin and NMMIIA in focal adhesions, and minimal intracellular collagen degradation. In fibroblasts plated on collagen-coated latex beads there are large increases of [Ca2+]i, time- and Ca2+-dependent enrichment of NMMIIA and gelsolin at collagen adhesions, and abundant intracellular collagen degradation. NMMIIA knockdown retards gelsolin recruitment to adhesions and blocks collagen phagocytosis. Gelsolin exhibits tight, Ca2+-dependent binding to full-length NMMIIA. Gelsolin domains G4–G6 selectively require Ca2+ to interact with NMMIIA, which is restricted to residues 1339–1899 of NMMIIA. We conclude that cell adhesion to collagen presented on beads activates Ca2+ entry and promotes the formation of phagosomes enriched with NMMIIA and gelsolin. The Ca2+ -dependent interaction of gelsolin and NMMIIA in turn enables actin remodeling and enhances collagen degradation by phagocytosis.  相似文献   

19.
E. A. C. MacRobbie 《Planta》1989,178(2):231-241
The influx of 45Ca into isolated guard cells of Commelina communis L. has been measured, using short uptake times, and washing in ice-cold La3+-containing solutions to remove extracellular tracer after the loading period. Over 0.5–4 min the uptake was linear with time, through the origin. Over 20–200M external Ca2+ the influx measured with 10–20 mM external KCl was in the range 0.3–2.3 pmol·cm-2·s-1 (on the basis of estimated guard-cell area); with only 1 mM KCl externally the 45Ca influx was significantly reduced, in the range 0.3–1.1 pmol·cm-2·s-1 for external Ca2+ of 50–100 M. The results indicate that the Ca-channel is voltage-sensitive, opening with depolarisation. No consistent effect of the addition of abscisic acid could be found. In different experiments, on the addition of 0.1 mM abscisic acid the Ca2+ influx was sometimes stimulated by 28–79%, was sometimes unaffected, and was sometimes inhibited by 16–29%. The results rule out a long-lasting stimulation of 45Ca influx by ABA, but they do not rule out a transient stimulation followed by inhibition, perphaps as a consequence of down-regulation of Ca2+ influx by increasing cytoplasmic Ca2+. The hypothesis that ABA may act via an action on Ca2+ influx, increasing cytoplasmic Ca2+, with consequent effects on voltage-dependent and Ca2+-dependent ion channels in both plasmalemma and tonoplast, is neither proved nor disproved by these results.Abbreviations ABA abscisic acid - Cao, Ko external Ca and K concentrations  相似文献   

20.
Macrophage polykaryons associated with the foreign body granuloma display several electrophysiological properties when studied with intracellular microelectrodes. One of the most evident properties is the slow hyperpolarization (2–5 s long, 10–60 mV amplitude), due to transient openings of Ca2+-dependent K+ channels, that is similar to those observed in macrophages. How this oscillation of membrane potential is triggered is not well known and the only way to repeatedly activate it under experimental control is through the intracellular injection of Ca2+. Although this technique is important for understanding the properties of the K+ channels, no information has been obtained about the way Ca2+ levels are raised and controlled in the cytosol. Slow hyperpolarizations can also be triggered by electrical stimulation, but reproducibility is low with cells bathed in physiological solutions. We then decided to investigate the effect of depolarization on the electrophysiological properties of macrophage polykaryons exposed to bathing solutions of several ionic compositions. We show in this paper that cell membrane depolarization induced by a long current pulse can trigger several patterns of membrane potential changes and that, in the absence of extracellular Na+, repetitive oscillations of decaying amplitudes are observed in almost all the cells. They are very similar to the slow hyperpolarizations, are dependent on the presence of extracellular Ca2+, and are blocked by quinine and D-600. Whole-cell patch clamp recording under voltage clamp conditions showed an outward current that oscillates and that also exhibits decaying amplitudes. The data presented here indicate that these oscillations are a consequence of the cyclic opening of the Ca2+-activated K+ channels and support the hypothesis that favors the participation of Ca2+ channels and of the Ca2+/Na+ exchange system in their triggering. These two mechanisms are not enough to explain either why the K+ channels close or why the membrane potential returns to the original level at the end of each cycle. The possibility of using these oscillations as a model to study the slow hyperpolarization is discussed.  相似文献   

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