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1.
We obtained a polyclonal antibody against the WGA-binding protein (WGAbp) of Strongylocentrotus intermedius sperm, which is a membrane glycoprotein of 260 kD under non-reducing condition. Anti-WGAbp antibody induced increases in both intracellular Ca2+ ([Ca2+ ]i) and intracellular pH (pHi), resulting in the onset of the AR. The increases in [Ca2+ ]i and pHi required extracellular Ca2+ and Na+ , respectively, and were suppressed by the pretreatment with WGA, resulting in the inhibition of the AR. Anti-WGAbp antibody-induced AR was inhibited also by lowered extracellular pH. elevated K+ , removal of Na+ from seawater and the treatment with verapamil, a Ca2+ channel inhibitor. These inhibitory conditions are identical with those of the egg jelly-induced AR. Monovalent Fab fragments from anti-WGAbp antibody also induced the AR at relatively high concentration. These results suggest that the WGAbp on the sperm plasma membrane is involved in the regulation of Ca2+ influx and Na+ /H+ exchange associated with the AR of S. intermedius sperm. It is a strong candidate for the receptor of the AR-inducing substance in the egg jelly. 相似文献
2.
The lectin wheat germ agglutinin (WGA) inhibited the egg jelly-induced acrosome reaction (AR) of sperm of the sea urchin, Strongylocentrotus intermedius . Fluorescein-conjugated WGA applied to sperm bound to the acrosomal region, to the midpiece, and to the tip of the flagellum. These effects were not observed in the presence of N-acetly-D-glucosamine. When the egg jelly was replaced by artificial AR inducers such as A23187 or nigericin, the AR was not inhibited by WGA. Results obtained using a Ca2+ indicator fura-2, a pH indicator 2',7'-bis(carboxyethyl)carboxyfluorescein (BCECF) and a membrane potential sensitive dye 3,3'-dipentyl 2,2'-dioxacarbocyanine [diO-C5 (3)] showed that WGA suppresses the egg jelly-induced influx of Ca2+ and slightly suppresses the efflux of H+ caused by the egg jelly, whereas the depolarization of the plasma membrane by the egg jelly is remarkably amplified by the treatment with WGA. These results suggest that WGA affects the regulatory system of the ion fluxes associated with the AR. The target protein of WGA (WGA-binding protein) was a membrane glycoprotein of 260 kD under non-reducing condition. 相似文献
3.
Katsuaki Hoshino Takeshi Shimizu Yutaka Sendai Tatsuo Harumi Norio Suzuki 《Development, growth & differentiation》1992,34(4):403-411
We examined the effects of two egg jelly components, a fucose sulfate glycoconjugate (FSG) and sperm-activating peptide I (SAP-I: Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly), on the intracellular pH (pHi ) and Ca2+ ([Ca2+ ]i ) of spermatozoa of the sea urchin Hemicentrotus pulcherrimus . FSG and/or SAP-I induced elevations of [Ca2+ ]; and pHi in the spermatozoa at pH 8.0. At pH 8.0, a second addition of FSG did not induced further elevation of the [Ca2+ ]i or pHi of spermatozoa treated with FSG, but addition or FSG after SAP-I or of SAP-I after FSG induced further increases of [Ca2+ ]i and pHi , At pH 6.6, FSG and/or SAP-I did not induce significant elevation of the [Ca2+ ]i , although SAP-I elevated the pHi , its half-maximal effective concentration being 10 to 100 pM. At pH 8.0, tetraethyl-ammonium, a voltage-sensitive K+ -channel blocker, inhibited induction of the acrosome reaction and elevations of [Ca2+ ]i and pHi by FSG, but did not affect those by SAP-I. These results suggest that FSG and SAP-I activate different Ca2+ and H+ transport systems. 相似文献
4.
Abstract: Increasing extracellular pH from 7.4 to 8.5 caused a dramatic increase in the time required to recover from a glutamate (3 µ M , for 15 s)-induced increase in intracellular Ca2+ concentration ([Ca2+ ]i ) in indo-1-loaded cultured cortical neurons. Recovery time in pH 7.4 HEPES-buffered saline solution (HBSS) was 126 ± 30 s, whereas recovery time was 216 ± 19 s when the pH was increased to 8.5. Removal of extracellular Ca2+ did not inhibit the prolongation of recovery caused by increasing pH. Extracellular alkalinization caused rapid intracellular alkalinization following glutamate exposure, suggesting that pH 8.5 HBSS may delay Ca2+ recovery by affecting intraneuronal Ca2+ buffering mechanisms, rather than an exclusively extracellular effect. The effect of pH 8.5 HBSS on Ca2+ recovery was similar to the effect of the mitochondrial uncoupler carbonyl cyanide p -(trifluoromethoxyphenyl)hydrazone (FCCP; 750 n M ). However, pH 8.5 HBSS did not have a quantitative effect on mitochondrial membrane potential comparable to that of FCCP in neurons loaded with a potential-sensitive fluorescent indicator, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbocyanine iodide (JC-1). We found that the effect of pH 8.5 HBSS on Ca2+ recovery was completely inhibited by the mitochondrial Na+ /Ca2+ exchange inhibitor CGP-37157 (25 µ M ). This suggests that increased mitochondrial Ca2+ efflux via the mitochondrial Na2+ /Ca2+ exchanger is responsible for the prolongation of [Ca2+ ]i recovery caused by alkaline pH following glutamate exposure. 相似文献
5.
Abstract: The role of the Na+ /Ca2+ exchanger and intracellular nonmitochondrial Ca2+ pool in the regulation of cytosolic free calcium concentration ([Ca2+ ]i ) during catecholamine secretion was investigated. Catecholamine secretion and [Ca2+ ]i were simultaneously monitored in a single chromaffin cell. After high-K+ stimulation, control cells and cells in which the Na+ /Ca2+ exchange activity was inhibited showed similar rates of [Ca2+ ]i elevation. However, the recovery of [Ca2+ ]i to resting levels was slower in the inhibited cells. Inhibition of the exchanger increased the total catecholamine secretion by prolonging the secretion. Inhibition of the Ca2+ pump of the intracellular Ca2+ pool with thapsigargin caused a significant delay in the recovery of [Ca2+ ]i and greatly enhanced the secretory events. These data suggest that both the Na+ /Ca2+ exchanger and the thapsigargin-sensitive Ca2+ pool are important in the regulation of [Ca2+ ]i and, by modulating the time course of secretion, are important in determining the extent of secretion. 相似文献
6.
Tosikazu Amano Yoshihito Okita Motonori Hoshi 《Development, growth & differentiation》1993,35(5):521-529
Egg jelly induces the degradation of histones as well as the acrosome reaction in the spermatozoa of Asterina pectinifera . Much similar degradation of histones without any apparent morphological changes such as the acrosome reaction was induced in the spermatozoa by merely dispersing them into Na+ -free seawater. It required external Ca2+ much less than the jelly-induced one in normal seawater, and was not susceptible to Ca2+ -channel antagonists, verapamil and diltiazem. Once spermatozoa were incubated with egg jelly in Ca2+ -free seawater, they did not undergo the histone degradation even after subsequent addition of Ca2+ , but Na+ -free seawater rescued such blockage. Spontaneous acrosome reaction occurred in seawater containing 10–30 mM Na+ in a Ca2+ -dependent manner. This reaction was accompanied by a rapid increase in intracellular pH (pHi) followed by a large pHi decrease. Diltiazem blocked a large decrease in pHi but scarcely inhibited the acrosome reaction induced by low-Na+ seawater. Increasing K+ inhibited both pHi changes and the acrosome reaction induced by low-Na+ seawater. Decreasing pH of seawater also inhibited the pHi changes but did not affect the acrosome reaction. Strontium was also effective to induce a rapid increase, followed by a gradual decrease, in pHi and the acrosome reaction. 相似文献
7.
Abstract: Nitric oxide has been recognized in recent years as an important mediator of neuronal toxicity, which in many cases involves alterations of the cytoplasmic Ca2+ concentration ([Ca2+ ]i ). In [Ca2+ ]i fluorimetric experiments on cultured hippocampal neurons, the nitric oxide-releasing agent S -nitrosocysteine produced a delayed rise in [Ca2+ ]i over a 20-min exposure, which was accompanied by a progressive slowing of the kinetics of recovery from depolarization-induced [Ca2+ ]i transients. These effects were blocked by oxyhemoglobin and by superoxide dismutase, confirming nitric oxide as the responsible agent, and suggesting that they involved peroxynitrite formation. Similar alterations of [Ca2+ ]i homeostasis were produced by the mitochondrial ATP synthase inhibitor oligomycin, and when an ATP-regenerating system was supplied via the patch pipette in combined whole-cell patch-clamp-[Ca2+ ]i fluorimetry experiments, S -nitrosocysteine had no effect on the resting [Ca2+ ]i or on the recovery kinetics of [Ca2+ ]i transients induced by direct depolarization. We conclude that prolonged exposure to nitric oxide disrupts [Ca2+ ]i homeostasis in hippocampal neurons by impairing Ca2+ removal from the cytoplasm, possibly as a result of ATP depletion. The resulting persistent alterations in [Ca2+ ]i may contribute to the delayed neurotoxicity of nitric oxide. 相似文献
8.
Upon fertilization, the sea urchin egg synthesizes proteins which impart a Ca2+ dependence to M-phase onset. A potential target of this Ca2+ dependence may be CaM kinase-II (the multifunctional [type II] Ca2+ /calmodulin [CaM]-dependent protein kinase) which is necessary for nuclear envelope breakdown in fertilized sea urchin eggs. This study was intended to determine whether sea urchin CaMK-II is activated after fertilization and whether it interacts with other known M-phase regulators, such as p34cdc2 . We report that total CaMK-II activity, measured by solution assays, increases after fertilization, peaking just prior to cleavage. Interestingly, total CaMK-II activity continues to fluctuate, peaking again prior to second and third cleavage. Gel assays also reveal enhanced levels of the 56 and 62 kDa potential CaMK-II phosphoproteins after fertilization. Finally, CaMK-II activity and only the 62 kDa phosphoprotein physically associate with p34cdc2 , but again only after fertilization. These changes in CaMK-II activity and p34cdc2 -association after fertilization may ensure that Ca2+ signals are targeted to the M-phase machinery at the appropriate developmental times. 相似文献
9.
Tadashi Tojo Yasuyuki Kamata Akiko Fujiwara Ikuo Yasumasu 《Development, growth & differentiation》1995,37(1):49-56
In sea urchin eggs, 10 μg/mL melittin was found to induce fertilization envelope formation without any increase in [Ca2+ ]i (the intracellular free Ca2+ level). On the other hand, 10 μmol/L Br-A23187 and 100 μg/mL SDS induced fertilization envelope formation associated with [Ca2+ ]i increase. If EGTA was injected into eggs to make an intracellular concentration of 2 mmol/L, [Ca2+ ]i became quite low and was not altered by melittin, or by Br-A23187 and SDS. In eggs containing EGTA, fertilization envelope formation was induced by melittin even in Ca2+ -free artificial sea water, but not by Br-A23187 or SDS. Thus [Ca2+ ]i is essential for induction of a fertilization envelope in sea urchin eggs by Br-A23187 or SDS but not by melittin. Melittin probably activates some Ca2+ -independent reaction downstream of Ca2+ -dependent reactions in a sequential reaction system that finally results in fertilization envelope formation. 相似文献
10.
Abstract: Human NT2-N neurons express Ca2+ -permeable α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid glutamate receptors (AMPA-GluRs) and become vulnerable to excitotoxicity when AMPA-GluR desensitization is blocked with cyclothiazide. Although the initial increase in intracellular Ca2+ levels ([Ca2+ ]i ) was 1.9-fold greater in the presence than in the absence of cyclothiazide, Ca2+ entry via AMPA-GluRs in an early phase of the exposure was not necessary to elicit excitotoxicity in these neurons. Rather, subsequent necrosis was caused by a >40-fold rise in [Na+ ]i , which induced a delayed [Ca2+ ]i rise. Transfer of the neurons to a 5 m M Na+ medium after AMPA-GluR activation accelerated the delayed [Ca2+ ]i rise and intensified excitotoxicity. Low-Na+ medium-enhanced excitotoxicity was partially blocked by amiloride or dizocilpine (MK-801), and completely blocked by removal of extracellular Ca2+ , suggesting that Ca2+ entry by reverse operation of Na+ /Ca2+ exchangers and via NMDA glutamate receptors was responsible for the neuronal death after excessive Na+ loading. Our results serve to emphasize the central role of neuronal Na+ loading in AMPA-GluR-mediated excitotoxicity in human neurons. 相似文献
11.
Talvinder S. Sihra Daniele Piomelli Robert A. Nichols 《Journal of neurochemistry》1993,61(4):1220-1230
Abstract: During K+ -induced depolarization of isolated rat brain nerve terminals (synaptosomes), 1 m M Ba2+ could substitute for 1 m M Ca2+ in evoking the release of endogenous glutamate. In addition, Ba2+ was found to evoke glutamate release in the absence of K+ -induced depolarization. Ba2+ (1–10 m M ) depolarized synaptosomes, as measured by voltage-sensitive dye fluorescence and [3 H]-tetraphenylphosphonium cation distribution. Ba2+ partially inhibited the increase in synaptosomal K+ efflux produced by depolarization, as reflected by the redistribution of radiolabeled 86 Rb+ . The release evoked by Ba2+ was inhibited by tetrodotoxin (TTX). Using the divalent cation indicator fura-2, cytosolic [Ca2+ ] increased during stimulation by approximately 200 n M , but cytosolic [Ba2+ ] increased by more than 1 μ M . Taken together, our results indicate that Ba2+ initially depolarizes synaptosomes most likely by blocking a K+ channel, which then activates TTX-sensitive Na+ channels, causing further depolarization, and finally enters synaptosomes through voltage-sensitive Ca2+ channels to evoke neurotransmitter release directly. Though Ba2+ -evoked glutamate release was comparable in level to that obtained with K+ -induced depolarization in the presence of Ca2+ , the apparent intrasynaptosomal level of Ba2+ required for a given amount of glutamate release was found to be several-fold higher than that required of Ca2+ . 相似文献
12.
Kari R. Hoyt Sunita Rajdev Cheryl L. Fattman Ian J. Reynolds 《Journal of neurochemistry》1995,64(5):2049-2056
Abstract: We investigated the modulation of (±)-α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)-induced increases in intracellular free Ca2+ ([Ca2+ ]i ) and intracellular free Mg2+ ([Mg2+ ]i ) by cyclothiazide and GYKI 52466 using microspectrofluorimetry in single cultured rat brain neurons. AMPA-induced changes in [Ca2+ ]i were increased by 0.3–100 µ M cyclothiazide, with an EC50 value of 2.40 µ M and a maximum potentiation of 428% of control values. [Ca2+ ]i responses to glutamate in the presence of N -methyl- d -aspartate (NMDA) receptor antagonists were also potentiated by 10 µ M cyclothiazide. The response to NMDA was not affected, demonstrating specificity of cyclothiazide for non-NMDA receptors. Almost all neurons responded with an increase in [Ca2+ ]i to both kainate and AMPA in the absence of extracellular Na+ , and these Na+ -free responses were also potentiated by cyclothiazide. GYKI 52466 inhibited responses to AMPA with an IC50 value of 12.0 µ M . Ten micromolar cyclothiazide significantly decreased the potency of GYKI 52466. However, the magnitude of this decrease in potency was not consistent with a competitive interaction between the two ligands. Cyclothiazide also potentiated AMPA- and glutamate-induced increases in [Mg2+ ]i . These results are consistent with the ability of cyclothiazide to decrease desensitization of non-NMDA glutamate receptors and may provide the basis for the increase in non-NMDA receptor-mediated excitotoxicity produced by cyclothiazide. 相似文献
13.
Masaru Sorimachi Yumiko Abe †Katsutoshi Furukawa ‡Norio Akaike 《Journal of neurochemistry》1995,64(3):1169-1174
Abstract: We examined the mechanism underlying the ATP-induced increase in the cytosolic Ca2+ concentration ([Ca]in ) in acutely isolated chick ciliary ganglion neurons, using fura-2 microfluorometry. The ATP-induced increase in [Ca]in was dependent on external Ca2+ , was blocked in a dose-dependent manner by reactive blue 2, and was substantially inhibited by both L- and N-type Ca2+ channel blockers. ATP was effective in increasing [Ca]in in the presence of a desensitizing concentration of nicotine (100 µ M ), and simultaneous addition of maximal doses of ATP and nicotine caused an additive increase in [Ca]in , suggesting that ATP acts on a site distinct from nicotinic acetylcholine receptors. ATP also increased the cytosolic Na+ concentration as determined by sodium-binding benzofuran isophthalate microfluorometry. These results suggest that ATP increases Na+ influx through P2 purinoceptor-associated channels resulting in membrane depolarization, which in turn increases Ca2+ influx through voltage-dependent Ca2+ channels. However, ATP still caused a small increase in [Ca]in under Na+ -free conditions, and this [Ca]in increase was little affected by Ca2+ channel blockers. ATP also increased Mn2+ influx under Na+ -free conditions, as indicated by quenching of fura-2 fluorescence. These results suggest that nonselective cationic channels activated by ATP are permeable not only to Ca2+ but also to Mn2+ , in addition to monovalent cations. 相似文献
14.
† Noriko Mochizuki-Oda †Yuko Takeuchi †‡Kiyoshi Matsumura Yoshio Oosawa †‡Yasuyoshi Watanabe 《Journal of neurochemistry》1997,69(1):377-387
Abstract: Hypoxia (5% O2 ) enhanced catecholamine release in cultured rat adrenal chromaffin cells. Also, the intracellular free Ca2+ concentration ([Ca2+ ]i ) increased within 3 min in ∼50% of the chromaffin cells under hypoxic stimulation. The increase depended on the presence of extracellular Ca2+ . Nifedipine and ω-conotoxin decreased the population of the cells that showed the hypoxia-induced [Ca2+ ]i increase, showing that the Ca2+ influx was attributable to L- and N-type voltage-dependent Ca2+ channels. The membrane potential was depolarized during the perfusion with the hypoxic solution and returned to the basal level following the change to the normoxic solution (20% O2 ). Membrane resistance increased twofold under the hypoxic condition. The current-voltage relationship showed a hypoxia-induced decrease in the outward K+ current. Among the K+ channel openers tested, cromakalim and levcromakalim, both of which interact with ATP-sensitive K+ channels, inhibited the hypoxia-induced [Ca2+ ]i increase and catecholamine release. The inhibitory effects of cromakalim and levcromakalim were reversed by glibenclamide and tolbutamide, potent blockers of ATP-sensitive K+ channels. These results suggest that some fractions of adrenal chromaffin cells are reactive to hypoxia and that K+ channels sensitive to cromakalim and glibenclamide might have a crucial role in hypoxia-induced responses. Adrenal chromaffin cells could thus be a useful model for the study of oxygen-sensing mechanisms. 相似文献
15.
In freshwater (FW) rainbow trout Oncorhynchus mykiss of spontaneously low plasma calcium concentrations ([Ca2+ ]pl ), plasma melatonin at night was significantly lower than that measured in FW fish with the highest [Ca2+ ]pl . In brackish water adapted rainbow trout with originally high [Ca2+ ]pl , plasma melatonin concentration at night was elevated. In cannulated flounder Platichthys flesus , night plasma melatonin increases (ΔMel) corresponded to [Ca2+ ]pl . It is postulated that in physiological steady-state conditions, melatonin synthesis capacity is coupled to free calcium concentration in plasma of O. mykiss and P. flesus . 相似文献
16.
Abstract: Nitric oxide (NO) has been shown to be an important mediator in several forms of neurotoxicity. We previously reported that NO alters intracellular Ca2+ concentration ([Ca2+ ]i ) homeostasis in cultured hippocampal neurons during 20-min exposures. In this study, we examine the relationship between late alterations of [Ca2+ ]i homeostasis and the delayed toxicity produced by NO. The NO-releasing agent S -nitrosocysteine (SNOC; 300 µ M ) reduced survival by about one half 1 day after 20-min exposures, as did other NO-releasing agents. SNOC also was found to produce prolonged elevations of [Ca2+ ]i , persisting at 2 and 6 h. Hemoglobin, a scavenger of NO, blocked both the late [Ca2+ ]i elevation and the delayed toxicity of SNOC. Removal of extracellular Ca2+ during the 20-min SNOC treatment failed to prevent the late [Ca2+ ]i elevations and did not prevent the delayed toxicity, but removal of extracellular Ca2+ for the 6 h after exposure as well blocked most of the toxicity. Western blots showed that SNOC exposure resulted in an increased proteolytic breakdown of the structural protein spectrin, generating a fragment with immunoreactivity suggesting activity of the Ca2+ -activated protease calpain. The spectrin breakdown and the toxicity of SNOC were inhibited by treatment with calpain antagonists. We conclude that exposures to toxic levels of NO cause prolonged disruption of [Ca2+ ]i homeostatic mechanisms, and that the resulting persistent [Ca2+ ]i elevations contribute to the delayed neurotoxicity of NO. 相似文献
17.
Abstract: The Na+ /Ca2+ exchanger is an important element in the maintenance of calcium homeostasis in bovine chromaffin cells. The Na+ /Ca2+ exchanger from other cell types has been extensively studied, but little is known about its regulation in the cell. We have investigated the role of reversible protein phosphorylation in the activity of the Na+ /Ca2+ exchanger of these cells. Cells treated with 1 m M dibutyryl cyclic AMP (dbcAMP), 1 µ M phorbol 12,13-dibutyrate, 1 µ M okadaic acid, or 100 n M calyculin A showed lowered Na+ /Ca2+ exchange activity and prolonged cytosolic Ca2+ transients caused by depolarization. A combination of 10 n M okadaic acid and 1 µ M dbcAMP synergistically inhibited Na+ /Ca2+ exchange activity. Conversely, 50 µ M 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, a protein kinase inhibitor, enhanced Na+ /Ca2+ exchange activity. Moreover, we used cyclic AMP-dependent protein kinase and calcium phospholipid-dependent protein kinase catalytic subunits to phosphorylate isolated membrane vesicles and found that the Na+ /Ca2+ exchange activity was inhibited by this treatment. These results indicate that reversible protein phosphorylation modulates the activity of the Na+ /Ca2+ exchanger and suggest that modulation of the exchanger may play a role in the regulation of secretion. 相似文献
18.
Abstract: The effects of peroxides were investigated on the membrane potential, intracellular Na+ ([Na+ ]i ) and intracellular Ca2+ ([Ca2+ ]i ) concentrations, and basal glutamate release of synaptosomes. Both H2 O2 and the organic cumene hydroperoxide produced a slow and continuous depolarization, parallel to an increase of [Na+ ]i over an incubation period of 15 min. A steady rise of the [Ca2+ ]i due to peroxides was also observed that was external Ca2+ dependent and detected only at an inwardly directed Ca2+ gradient of the plasma membrane. These changes did not correlate with lipid peroxidation, which was elicited by cumene hydroperoxide but not by H2 O2 . Resting release of glutamate remained unchanged during the first 15 min of incubation in the presence of peroxides. These alterations may indicate early dysfunctions in the sequence of events occurring in the nerve terminals in response to oxidative stress. 相似文献
19.
Ludger Johannes Pierre-Marie Lledo †Pascal Chameau Jean-Didier Vincent Jean-Pierre Henry François Darchen 《Journal of neurochemistry》1998,71(3):1127-1133
Abstract: Ca2+ ions trigger the release of hormones and neurotransmitters and contribute to making the secretory vesicles competent for fusion. Here, we present evidence for the involvement of the GTP-binding protein Rab3a in the sensitivity of the exocytotic process to internal [Ca2+ ]. The secretory activity of bovine adrenal chromaffin cells was elicited by Ca2+ dialysis through a patch-clamp pipette and assayed by monitoring changes in cell membrane capacitance. Microinjection of antisense oligonucleotides directed to rab3a mRNA increased the secretory activity observed at low (0.2–4 µ M ) [Ca2+ ], but did not change the maximal activity observed at 10 µ M free [Ca2+ ]. Moreover, after a train of depolarizing stimuli, the secretory activity of antisense-injected cells dialyzed with 10 µ M [Ca2+ ] was increased significantly compared with that of control cells. This result suggests that the activity of either Rab3a or its partners might change upon stimulation. We conclude that Rab3a, together with its partners, participates in the Ca2+ dependence of exocytosis and that its activity is modulated further in a stimulus-dependent manner. These findings should provide some clues to elucidate the role of Rab3a in synaptic plasticity. 相似文献
20.
Peter B. Simpson R. A. John Challiss Stefan R. Nahorski 《Journal of neurochemistry》1993,61(2):760-763
Abstract: The [Ca2+ ]1 of cerebellar granule cells can be increased in a biphasic manner by addition of NMDA or by depolarization (induced by elevating the extracellular K+ level), which both activate Ca2+ influx. The possibility that these stimuli activate Ca2+ -induced Ca2+ release was investigated using granule cells loaded with fura 2-AM. Dantrolene, perfused onto groups of cells during the sustained plateau phase of the [Ca2+ ]1 response to K+ or NMDA, was found to reduce the response to both agents in a concentration-dependent manner. Preincubation with thapsigargm (10 μ M ) substantially reduced the plateau phase of the [Ca2+ ], response to K+ and both the peak and plateau phases of the NMDA response. Preincubation with ryanodine (10 μ M ) also reduced both the K+ -evoked plateau response and both phases of the NMDA response. Neither had a consistent effect on the peak response to K+ . The effects of thapsigargin and ryanodine on the NMDA response were partially additive. These results demonstrate that in cerebellar granule cells a major component of both K+ - and NMDA-induced elevation of [Ca2+ ]1 appears to be due to release from intracellular stores. The partial additivity of the effects of thapsigargin and ryanodine suggests that these agents affect two overlapping but nonidentical Ca2+ pools. 相似文献