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1.
l-Glutamic acid actively loaded into resealed brain synaptic membrane vesicles was rapidly released into the incubation medium following the introduction of KCl and CaCl2, or nigericin, or veratridine into the external medium. The KCl-induced release was enhanced by the presence of low (0.1 mM), extravesicular [Ca2+]. Neither the KCl-induced nor the veratridine-stimulated l-glutamate efflux were carrier-mediated processes. Finally, the KCl-stimulated l-glutamate efflux was dependent on the ratio of intra- to extravesicular [K+]. The observations described in this study were indicative of depolarization-induced l-glutamate release from isolated synaptic plasma membrane vesicles. 相似文献
2.
Chinopoulos C Starkov AA Grigoriev S Dejean LM Kinnally KW Liu X Ambudkar IS Fiskum G 《Journal of bioenergetics and biomembranes》2005,37(4):237-247
Mitochondria contribute to cytosolic Ca2+ homeostasis through several uptake and release pathways. Here we report that 1,2-sn-diacylglycerols (DAGs) induce Ca2+ release from Ca2+-loaded mammalian mitochondria. Release is not mediated by the uniporter or the Na+/Ca2+ exchanger, nor is it attributed to putative catabolites. DAGs-induced Ca2+ efflux is biphasic. Initial release is rapid and transient, insensitive to permeability transition inhibitors, and not accompanied by mitochondrial swelling. Following initial rapid release of Ca2+ and relatively slow reuptake, a secondary progressive release of Ca2+ occurs, associated with swelling, and mitigated by permeability transition inhibitors. The initial peak of DAGs-induced Ca2+ efflux is abolished by La3+ (1 mM) and potentiated by protein kinase C inhibitors. Phorbol esters, 1,3-diacylglycerols and 1-monoacylglycerols do not induce mitochondrial Ca2+ efflux. Ca2+-loaded mitoplasts devoid of outer mitochondrial membrane also exhibit DAGs-induced Ca2+ release, indicating that this mechanism resides at the inner mitochondrial membrane. Patch clamping brain mitoplasts reveal DAGs-induced slightly cation-selective channel activity that is insensitive to bongkrekic acid and abolished by La3+. The presence of a second messenger-sensitive Ca2+ release mechanism in mitochondria could have an important impact on intracellular Ca2+ homeostasis. 相似文献
3.
Rilmenidine Elevates Cytosolic Free Calcium Concentration in Suspended Cerebral Astrocytes 总被引:1,自引:0,他引:1
Mark A. Ozog John X. Wilson †S. Jeffrey Dixon David F. Cechetto 《Journal of neurochemistry》1998,71(4):1429-1435
Abstract: Rilmenidine, a ligand for imidazoline and α2-adrenergic receptors, is neuroprotective following focal cerebral ischemia. We investigated the effects of rilmenidine on cytosolic free Ca2+ concentration ([Ca2+]i) in rat astrocytes. Rilmenidine caused concentration-dependent elevation of [Ca2+]i, consisting of a transient increase (1–100 µM rilmenidine) or a transient increase followed by sustained elevation above basal levels (1–10 mM rilmenidine). A similar elevation in [Ca2+]i was induced by the imidazoline ligand cirazoline. The transient response to rilmenidine was observed in Ca2+-free medium, indicating that rilmenidine evokes release of Ca2+ from intracellular stores. However, the sustained elevation of Ca2+ was completely dependent on extracellular Ca2+, consistent with rilmenidine activating Ca2+ influx.Pretreatment with thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, abolished the response to rilmenidine, confirming the involvement of intracellular stores and suggesting that rilmenidine and thapsigargin activate a common Ca2+ influx pathway. The α2-adrenergic antagonist rauwolscine attenuated the increase in [Ca2+]i induced by clonidine (a selective α2 agonist), but not the response to rilmenidine. These results indicate that rilmenidine stimulates both Ca2+ release from intracellular stores and Ca2+ influx by a mechanism independent of α2-adrenergic receptors. In vivo, rilmenidine may enhance uptake of Ca2+ from the extracellular fluid by astrocytes, a process that may contribute to the neuroprotective effects of this agent. 相似文献
4.
When guinea pig spermatozoa are preincubated for 1 hr in Ca2+?free medium containing a low concentration of lysolecithin (LC, 85 μg/ml) and then exposed to 2 mM Ca2+ by diluting the preincubation medium with an equal volume of LC?free, 4 mM Ca2+?containing medium, the majority of the spermatozoa undergo acrosome reaction promptly. On the other hand, when the preincubated spermatozoa are exposed to 2 mM Ca2+ without reducing the original concentration of LC in the medium, none of them undergo acrosome reaction. These spermatoza can acrosome?react if they are transferred to an LC?free medium. These results and those of some other experiments suggest that in the presistent presence of a high concentration of LC in the medium, exogenous Ca2+ essential for the acrosome reaction either does not penetrate the sperm plasma membrane or, if it does, it cannot alter the membrane for the acrosome reaction, at least under the experimental conditions employed. Freeze?fracture examination of the sperm plasma membrane has revealed that small areas or patches free of intramembranous paarticles (IMPs) appear in the membrance during sperm preincubation, and these IMP?free areas expand drastically in response to Ca2+ when the LC conccentration in the medium is reduced at the time Ca2+ is added to the medium. In contrast, IMP?free areas remain unchanged even after exposure of spermatozoa to Ca2+ if the concentration of LC remains at its original level of 85 μg/ml. 相似文献
5.
Luowei Li Robert W. Tucker Henry Hennings Stuart H. Yuspa 《Journal of cellular physiology》1995,163(1):105-114
The role of intracellular Ca2+ in the regulation of Ca2+-induced terminal differentiation of mouse keratinocytes was investigated using the intracellular Ca2+ chelator 1,2-bis(o-aminophenoxy)-ethane-N, N, N′, N′-tetraacetic acid (BAPTA). A cell permeable acetoxymethyl (AM) ester derivative BAPTA (BAPTA/AM) was loaded into primary mouse keratinocytes in 0.05 mM Ca2+ medium, and then the cells were induced to differentiate by medium containing 0.12 or 0.5 mM Ca2+. Intracellular BAPTA loaded by BAPTA/AM (15–30 μM) inhibited the expression of epidermal differentiation-specific proteins keratin 1 (K1), keratin 10 (K10), filaggrin and loricrin as detected by immunoblotting. The differentiation-associated redistribution of E-cadherin on the cell membrane was delayed but not inhibited as determined by immunofluorescence. BAPTA also inhibited the expression of K1, K10 and Ioricrin mRNA. Furthermore, BAPTA prevented the decrease in DNA synthesis induced by 0.12 and 0.5 mM Ca2+, indicating the drug was inhibiting differentiation but was not toxic to keratinocytes. To evaluate the influence of BAPTA on intracellular Ca2+, the concentration of intracellular free Ca2+ (Cai) in BAPTA-loaded keratinocytes was examined by digital image analysis using the Ca2+-sensitive fluorescent probe fura-2, and Ca2+ influx was measured by 45Ca2+ uptake studies. Increase in extracellular Ca2+ (Cao) in the culture medium of keratinocytes caused a sustained increase in both Cai and Ca2+ localized to ionomycin-sensitive intracellular stores in keratinocytes. BAPTA lowered basal Cai concentration and prevented the Cai increase. After 12 hours of BAPTA treatment, the basal level of Cai returned to the control value, but the Ca2+ localized in intracellular stores was substantially decreased. 45Ca2+ uptake was initially (within 30 min) increased in BAPTA-loaded cells. However, the total 45Ca2+ accumulation over 24 hours in BAPTA-loaded cells remained unchanged from control values. These results indicate that keratinocytes can maintain Cai and total cellular Ca2+ content in the presence of increased amount of intracellular Ca2+ buffer (e.g., BAPTA) by depleting intracellular Ca2+ stores over a long period. The inhibition by BAPTA of keratinocyte differentiation marker expression may result from depletion of the Ca2+-stores since this is the major change in intracellular Ca2+ detected at the time keratinocytes express the differentiation markers. In contrast, the redistribution of E-cadherin on the cell membrane may be more directly associated with Cai change. © 1995 Wiley-Liss, Inc. 相似文献
6.
The possible role of metalloendoproteinase in stimulus-secretion coupling in adrenal chromaffin cells was examined using the metalloendoproteinase inhibitors 1,10-phenanthroline and carbobenzoxy-Gly-Phe-NH2. Catecholamine release elicited by nicotine or by depolarisation with 55 mM K+ was almost completely abolished by 0.5 mM 1,10-phenanthroline. Carbobenzoxy-Gly-Phe-NH2 (2.5 mM) inhibited catecholamine release in response to nicotine but enhanced that due to 55 mM K+. The rise in intracellular free calcium, [Ca2+]i, in response to either nicotine or 55 mM was inhibited by about 50% by both inhibitors. One site of action of metalloendoproteinase inhibitors may, therefore, be at the level of the regulation of [Ca2+]i. Catecholamine release and the rise in [Ca2+]i elicited by the calcium ionophore ionomycin were not reduced by the inhibitors. These results show that metalloendoproteinase inhibitors have complex effects on chromaffin cells including effects on the regulation of [Ca2+]i but do not inhibit calcium-activated exocytosis itself. 相似文献
7.
《Cell communication & adhesion》2013,20(4):343-353
The intracellular free Ca2+ ion concentration ([Ca2+]i) was measured using fura-2 microspec-trofluorimetry in individual rat pancreatic β-cells prepared by enzymatic digestion and fluorescence-activated cell sorting. The mean basal concentration of [Ca2+]i in β-cells in the presence of 4.4 mM glucose and 1.8 mM Ca2+ was 112±1.6 nM (n=207). The action of acetylcholine (ACh) was concentration-dependent, and raising the concentration resulted in [Ca2+]i spikes of increasing amplitude and duration in some, but not all of the β-cells. In addition, the β-cells demonstrated variable sensitivity to ACh. The increases in [Ca2+]i were rapid, transient and were blocked by atropine at 10?6M. A brief exposure to 50 mM K+ resulted in a transient increase in [Ca2+]i similar to that induced by ACh, but resistant to atropine. A high concentration of ACh (100μL 10?4M or 10?3M) induced [Ca2+]i oscillations in 11 out of 57 β-cells in the presence of 4.4 mM glucose. Using calcium channel blockers and Ca2+ free medium, the source of the increase in [Ca2+]i was deduced to be from extracellular spaces. Changing the temperature from 22 to 37°C did not affect the action of ACh on [Ca2+]i. These data strongly suggest that ACh exerted a direct action on [Ca2+]i in normal rat pancreatic β-cells and support a role for Ca2+ as a second messenger in the action of ACh. 相似文献
8.
Dimethyl sulfoxide (DMSO) initiates a coordinated differentiation program in various cell types but the mechanism(s) by which DMSO does this is not understood. In this study, the effect of DMSO on intracellular calcium ion concentration ([Ca2+]i) was determined in primary cultures of chicken ovarian granulosa cells from the two largest preovulatory follicles of laying hens, and in three cell lines: undifferentiated P19 embryonal carcinoma cells, 3T3-L1 fibroblasts, and Friend murine erythroleukemia (MEL) cells. [Ca2+]i was measured in cells loaded with the Ca2+ -specific fluoroprobe Fura-2. There was an immediate (i.e., within 5 sec), transient, two to sixfold increase in [Ca2+]i after exposing all cell types to 1% DMSO. DMSO was effective between 0.2 and 1%. The prompt DMSO-induced [Ca2+]i spike in all of the cell types was not prevented by incubating the cells in Ca2+ -free medium containing 2 mM EGTA or by pretreating them with the Ca2+-channel blockers methoxyverapamil (D600; 100 μM), nifedipine (20 μM), or cobalt (5 mM). However, when granulosa cells, 3T3-L1 cells, or MEL cells were pretreated with lanthanum (La3+; 1 mM), which blocks both Ca2+ channels and membrane Ca2+ pumps, there was a sustained increase in [Ca2+]i in response to 1% DMSO. By contrast, pretreating P19 cells with La3+ (1 mM) did not prolong the DMSO-triggered [Ca2+]i transient. In all cases, the DMSO-induced [Ca2+]i surge was unaffected by pretreating the cells with the inhibitors of inositol phospholipid hydrolysis, neomycin (1.5 mM) or U-73, 122 (2.5 μM). These results suggest that DMSO almost instantaneously triggers the release of Ca2+ from intracellular stores through a common mechanism in cells in primary cultures and in cells of a variety of established lines, but, this release is not mediated through phosphoinositide breakdown. This large, DMSO-induced Ca2+ spike may play a role in the induction of cell differentiation by DMSO. © 1993 Wiley-Liss, Inc. 相似文献
9.
We evaluated mechanisms which mediate alterations in intracellular biochemical events in response to transient mechanical
stimulation of colonic smooth muscle cells. Cultured myocytes from the circular muscle layer of the rabbit distal colon responded
to brief focal mechanical deformation of the plasma membrane with a transient increase in intracellular calcium concentration
([Ca2+]
i
) with peak of 422.7 ± 43.8 nm above an average resting [Ca2+]
i
of 104.8 ± 10.9 nm (n= 57) followed by both rapid and prolonged recovery phases. The peak [Ca2+]
i
increase was reduced by 50% in the absence of extracellular Ca2+, while the prolonged [Ca2+]
i
recovery was either abolished or reduced to ≤15% of control values. In contrast, no significant effect of gadolinium chloride
(100 μm) or lanthanum chloride (25 μm) on either peak transient or prolonged [Ca2+]
i
recovery was observed. Pretreatment of cells with thapsigargin (1 μm) resulted in a 25% reduction of the mechanically induced peak [Ca2+]
i
response, while the phospholipase C inhibitor U-73122 had no effect on the [Ca2+]
i
transient peak. [Ca2+]
i
transients were abolished when cells previously treated with thapsigargin were mechanically stimulated in Ca2+-free solution, or when Ca2+ stores were depleted by thapsigargin in Ca2+-free solution. Pretreatment with the microfilament disrupting drug cytochalasin D (10 μm) or microinjection of myocytes with an intracellular saline resulted in complete inhibition of the transient. The effect
of cytochalasin D was reversible and did not prevent the [Ca2+]
i
increases in response to thapsigargin. These results suggest a communication, which may be mediated by direct mechanical
link via actin filaments, between the plasma membrane and an internal Ca2+ store.
Received: 24 March 1997/Revised: 21 July 1997 相似文献
10.
Yuji Shono Masahiro Kamouchi Takanari Kitazono Junya Kuroda Kuniyuki Nakamura Noriko Hagiwara Hiroaki Ooboshi Setsuro Ibayashi Mitsuo Iida 《Cellular and molecular neurobiology》2010,30(3):453-460
Brain hypoxia or ischemia causes acidosis and the intracellular accumulation of Ca2+ in neuron. The aims of the present study were to elucidate the interaction between intracellular pH and Ca2+ during transient acidosis and its effects on the viability of neuronal and glial cells. Intracellular Ca2+ and pH were measured using the fluorescence of fura-2 and 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl
ester in neuroblastoma (IMR-32), glioblastoma (T98G), and astrocytoma (CCF-STTG1) cell lines. The administration of 5 mM propionate
caused intracellular acidification in IMR-32 and T98G cells but not in CCF-STTG1 cells. After the removal of propionate, the
intracellular pH recovered to the resting level. The intracellular Ca2+ transiently increased upon the removal of propionate in IMR-32 and T98G cells but not in CCF-STTG1 cells. The transient Ca2+ increase caused by the withdrawal of intracellular acidification was abolished by the removal of external Ca2+, diminished by a reduction of external Na+, and inhibited by benzamil. Transient acidosis caused cell death, whereas the cells were more viable in the absence of external
Ca2+. Benzamil alleviated cell death caused by transient acidosis in IMR-32 and T98G cells but not in CCF-STTG1 cells. These results
suggest that recovery from intracellular acidosis causes a transient increase in cytosolic Ca2+ due to reversal of Ca2+ transport via Na+/Ca2+ exchanger coactivated with Na+/H+ exchanger, which can cause cell death. 相似文献
11.
Pazdernik NJ Matzke EA Jessen-Marshall AE Brooker RJ 《The Journal of membrane biology》2000,176(1):31-40
Patients with cerebral tumors often present with elevated levels of acetylcholine (ACh) in their cerebrospinal fluid. This
motivated us to investigate physiological effects of ACh on cultured human astrocytoma cells (U373) using a combination of
videomicroscopy, calcium microspectrofluorimetry and perforated patch-clamp recording. Astrocytoma cells exhibited the typical
morphological changes associated with cell migration; polarized cells displayed prominent lamellipodia and associated membrane
ruffling at the anterior of the cell, and a long tail region that periodically contracted into the cell body as the cell moved
forward. Bath application of the ACh receptor agonist, muscarine, reversibly inhibited cell migration. In conjunction with
this inhibition, ACh induced a dose-dependent, biphasic increase in resting intracellular free calcium concentration ([Ca2+]
i
) associated with periodic Ca2+ oscillations during prolonged ACh applications. The early transient rise in [Ca2+]
i
was abolished by ionomycin and thapsigargin but was insensitive to caffeine and ryanodine while the plateau phase was strictly
dependent on external calcium. The Ca2+ response to ACh was mimicked by muscarine and abolished by the muscarinic antagonists, atropine or 4-DAMP, but not by pirenzepine.
Using perforated patch-clamp recordings combined with fluorescent imaging, we demonstrated that ACh-induced [Ca2+]
i
oscillations triggered membrane voltage oscillations that were due to the activation of voltage-dependent, Ca2+-sensitive K+ currents. These K+ currents were blocked by intracellular injection of EGTA, or by extracellular application of TEA, quinine, or charybdotoxin,
but not by apamin. These studies suggest that activation of muscarinic receptors on glioma cells induce the release of Ca2+ from intracellular stores which in turn activate Ca2+-dependent (BK-type) K+ channels. Furthermore, this effect was associated with inhibition of cell migration, suggesting an interaction of this pathway
with glioma cell migration.
Received: 17 December/Revised: 17 March 2000 相似文献
12.
《Insect Biochemistry》1988,18(4):359-362
The effect of taurine has been studied on 45Ca2+ efflux from mitochondria obtained from the flight muscle and thoracic ganglia of the desert locust. Mitochondria from both tissues readily accumulated 45Ca2+ and this uptake was stimulated by the presence of phosphate 45Ca2+ accumulation was abolished by ruthenium red (5 μ M). Only in the presence of 10 mM Na+ and either ruthenium red (5 μ M) or EGTA (500 μ M), was an efflux of 45Ca2+ observed. Taurine (20 mM) abolished the Na+-dependent 45Ca2+ efflux but had no effect in the absence of Na+. These results suggest that taurine may contribute to the control of the concentration of intracellular free calcium. 相似文献
13.
《Free radical research》2013,47(5):307-313
A self-referencing and non-invasive Ca2+-sensitive vibrating electrode was used to assess the effects of hydrogen peroxide-induced oxidative challenges on the efflux and influx of calcium across the plasma membrane of single nerve cells cultured from abdominal ganglion of Aplysia californica. A reduced net efflux of Ca2+ from the cell soma occurred immediately after the addition of hydrogen peroxide (0.0025 mM, 0.005 mM or 0.01 mM) to the culture medium, indicating damage to the cell membrane or Ca2+ transport mechanism. There then followed a marked efflux, the extent and duration of which was related to the concentration of hydrogen peroxide used and which may reflect compensatory activity by the Ca2+ regulatory mechanisms in the plasmalemma. No morphological changes were observed in cells challenged with 0.0025 mM hydrogen peroxide and the enhanced rate of Ca2+ efflux rapidly decreased to pre-exposure values. Sustained and enhanced Ca2+ effluxes from those cells exposed to 0.005 mM or 0.01 mM hydrogen peroxide were also consistent with regulatory pumping of Ca2+ out of the cell although contraction and blebbing of neurites and swelling of the soma may indicate that a proportion of the efflux arose from release of Ca2+ from disrupted intracellular stores. The vibrating electrode is a useful additional technique for the study of the pathogenesis of neurological conditions, as ionic fluxes across single nerve cells exposed to physiologically-relevant concentrations of free radicals can be monitored non-invasively for prolonged periods. 相似文献
14.
Abstract: Modes of Ca2+ activation by bradykinin, serotonin, and ATP and the possible receptor cross-talk were investigated in mouse neuroblastoma × rat glioma hybrid cells (108CC15) by monitoring fura-2 fluorescence in single cells. A transient rise of cytosolic Ca2+ activity was induced by short pulses of the hormones. Brief exposure of cells to ionomycin, which depletes intracellular Ca2+ stores, reduced the size of subsequent responses to bradykinin or ATP, but not to serotonin. Superfusion of the cells with Ca2+-free medium abolished the Ca2+ response to serotonin, whereas the responses to bradykinin and to ATP were only slightly reduced. This indicates that ATP, like bradykinin, Induces the release of Ca2+ from intracellular stores. Serotonin, in contrast, activates Ca2+ entry from the extracellular space. To investigate whether ATP releases Ca2+ from the same stores as bradykinin, we examined the interaction of the hormones by applying them consecutively. When ATP was applied after bradykinin, the nucleotide did not evoke any response, irrespective of the presence or absence of extracellular Ca2+. The application of ATP before that of bradykinin reduced the size of a following bradykinin-induced Ca2+ response in Ca2+-free medium, but not in Ca2+-containing medium. This suggests that bradykinin may interact with the ATP-activated mechanism by cross-desensitization. Possibly, bradykinin receptors are coupled to additional Ca2+ stores not accessible to ATP that are refilled by extracellular Ca2+. Cyclic AMP and cyclic GMP apparently do not affect the Ca2+ responses to bradykinin and serotonin, as shown by the lack of influence of preincubation of the cells with forskolin or sodium nitroprusside. 相似文献
15.
Summary The mechanism of Ca2+-dependent control of hypotonic cell volume regulation was investigated in the isolated, nonperfused renal proximal straight tubule. When proximal tubules were exposed to hypotonic solution with 1 mM Ca2+, cells swelled rapidly and then underwent regulatory volume decrease (RVD). This treatment resulted in an increase in intracellular free calcium concentration ([Ca2+]i) by a mechanism that had two phases: the first was a transient increase from baseline (136 nM) to a peak (413 nM) that occurred in the first 15–20 sec, but was followed by a rapid decay toward the pre-swelling levels. The second phase was characterized by a sustained elevation of [Ca2+]i above the baseline (269 nM), which was maintained over several minutes. The dependence of these two phases on extracellular Ca2+ was determined. Reduction of bath [Ca2+] to 10 or 1 M partially diminished the transient phase, but abolished the sustained phase completely, such that [Ca2+]i fell below the base-line levels during RVD. It was concluded that the transient increase resulted predominantly from swelling-activated release of intracellular Ca2+ stores and that the sustained phase was due to swelling-activated Ca2+ entry across the plasma membrane. Ca2+ entry probably also contributed to the transient increase in [Ca2+]i. The time dependence of swelling-activated Ca2+ entry was also investigated, since it was previously shown that RVD was characterized by a calcium window period (<60 sec). during which extracellular Ca2+ was required. Outside of this time period, RVD would inactivate and could not be reactivated by subsequent addition of Ca2+. It was found that the Ca2+ permeability did not inactivate over several minutes, indicating that the temporal dependence of RVD on extracellular Ca2+ is not due to the transient activation of a Ca2+ entry pathway. 相似文献
16.
Mateusz Koselski Kazimierz Trebacz Halina Dziubinska Elzbieta Krol 《Plant signaling & behavior》2008,3(1):13-18
Glass microelectrodes were inserted into Physcomitrella patens gametophyte leaves and action potentials (APs) were recorded in response to sudden illumination as well as after darkening, i.e., when the dark-induced membrane depolarization crossed a threshold. Application of 5 mM La3+ (a calcium channel inhibitor), 10 mM TEA+ (a potassium channel inhibitor) and increased free Ca2+ resulted in a loss of excitability. Lack of Ca2+ in the external medium did not prevent APs from occurring. It was concluded that during light- dark-induced excitation of Physcomitrella patens, APs might rely upon calcium influxes from the intracellular compartments. APs were not blocked by the proton pump inhibitors (DES, DCCD), although the resting potential (RP) diminished significantly.Key words: action potential, calcium, moss, Physcomitrella patens, plant 相似文献
17.
In the present study, the bombesin-induced changes in cytosolic free Ca2+ ([Ca2+]i) were investigated in single Fura-2 loaded SV-40 transformed hamster β-cells (HIT). Bombesin (50–500 pM) caused frequency-modulated repetitive Ca2+ transients. The average frequency of the Ca2+ transients induced by bombesin (200 pM) was 0.58 ± 0.02 min−1 (n = 121 cells). High concentrations of bombesin (≥ 2 nM) triggered a large initial Ca2+ transient followed by a sustained plateau or by a decrease to basal levels. In Ca2+- free medium, bombesin caused only one or two Ca2+ transients and withdrawal of extracellular Ca2+ abolished the Ca2+ transients. The voltage-dependent Ca2+ channel (VDCC) blockers, verapamil (50 μM) and nifedipine (10 μM), reduced amplitude and frequency of the Ca2+ transients and stopped the Ca2+ transients in some cells. Thapsigargin caused a sustained rise in [Ca2+]i) in the presence of extracellular Ca2+ while in its absence the rise in [Ca2+]i) was transient. Verapamil (50 μM) inhibited the thapsigargin-induced increase in [Ca2+], by about 50%. Depletion of intracellular Ca2+ stores by repetitive stimulation with increasing concentrations of bombesin or thapsigargin in Ca2+-free medium caused an agonist-independent increase in [Ca2+]i) when extracellular Ca2+ was restored, which was larger than in control cells that had been incubated in Ca2+-free medium for the same period of time. This rise in [Ca2+]i and the thapsigargin-induced increase in [Ca2+]i) were only partly inhibited by VDCC-blockers. Thus, depletion of the agonist-sensitive Ca2+ pool enhances Ca2+ influx through VDCC and voltage-independent Ca2+ channels (VICC). In conclusion, the bombesin-induced Ca2+ response in single HIT cells is periodic in nature with frequency-modulated repetitive Ca2+ transients. Intracellular Ca2+ is mobilized during each Ca2+ transient, but Ca2+ influx through VDCC and VICC is required for maintaining the sustained nature of the Ca2+ response. Ca2+ influx in whole or part is activated by a capacitative Ca2+ entry mechanism. 相似文献
18.
Experiments were carried out on isolated neurons of the thalamic nucleus lateralis dorsalis (LD) from 12-day-old rats. According to the morphological characteristics, LD neurons were classified as relay thalamo-cortical units and interneurons. The concentration of free Ca2+ ions in the cytoplasm ([Ca2+]
i
) was measured by a fluorescent calcium indicator, fura-2AM. Application of 30 mM caffeine caused a transient change in the [Ca2+]
i
in 8 of 15 and in 6 of 11 of the thalamo-cortical units and interneurons under study, respectively. After stimulation of a cell with application of 50 mM KCl, a caffeine-induced increase in the [Ca2+]
i
was observed in all tested neurons. To study the contribution of Ca2+-induced Ca2+ release (CICR) to the calcium transient evoked by depolarization of the neuronal membrane, caffeine in a subthreshold concentration was pre-applied. After 50 mM KCl had been added to the medium following pre-application of 0.5 mM caffeine, the calcium transient amplitude in thalamo-cortical neurons increased by 51 ± 7% (n = 16). In interneurons this effect was not observed (n = 11). The data obtained allow us to hypothesize that CICR contributes to the depolarization-evoked calcium transient only in the relay (thalamo-cortical) neurons. Differences in the pattern of calcium signalling, which were detected in two types of neurons of the thalamic LD, can be a factor determining distinctions in the physiological characteristics of these neurons. 相似文献
19.
We characterized the effects of histamine on intracellular Ca2+ and activation of ionic currents in human capillary endothelial cells. Histamine produced both a transient and sustained
increase in intracellular Ca2+. The transient response was mediated largely through intracellular Ca2+ release and the sustained response was due to extracellular Ca2+ entry. The increase in intracellular Ca2+ by histamine was not affected by the H2 blocker cimetidine. But was entirely blocked by the H1 antagonist diphenhydramine
showing that the histamine response in these cells is mediated through the H1 receptor. A transient ionic current is coactivated
with the histamine-induced increase in intracellular Ca2+ and this current has several properties of a nonselective, Ca2+ permeable, cation channel (NSC). The magnitude of the NSC current does not strictly correlate with intracellular Ca2+ levels. A Ca2+-activated K+ current (BKCA) is activated by the increase in intracellular Ca2+ and this current is blocked by the selective BKCA blocker iberiotoxin.
Received: 16 June 1999/Revised: 22 September 1999 相似文献
20.
《Journal of Physiology》1998,92(1):31-35
Perifused rat pancreatic islets, prelabelled with 45Ca, were exposed for 90 min to a medium containing 30 mM K+, 0.25 mM diazoxide and 0.5 mM EGTA, but deprived of CaCl2. Either verapamil (0.05 mM) or Cd2+ (0.05 mM) were also present in the perifusate. Under these conditions a rise in D-glucose concentrations from either 2.8 to 16.7 mM or zero to 8.3 mM increased both 45Ca outflow and insulin release, after an initial and transient decrease in effluent radioactivity. These findings suggest that, in islets depolarised by exposure to a high extracellular concentration of K+, D-glucose provokes an intracellular redistribution of Ca2+ ions and subsequent stimulation of insulin release. The functional response to D-glucose is apparently not attributable to either the closing of ATP-sensitive K+ channels, which were actually activated by diazoxide, or stimulation of Ca2+ influx, which was prevented by the absence of extracellular Ca2+. The present experimental design thus reveals a novel component of the glucose-induced remodelling of Ca2+ fluxes in islet cells. Such an effect might also be operative under physiological conditions, when the hexose leads to depolarisation of the islet B-cells. 相似文献