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1.
In response to stimuli, secretary cells secrete a variety of signaling molecules packed in vesicles (e.g., neurotransmitters
and peptide hormones) into the extracellular space by exocytosis. The vesicle secretion is often triggered by calcium ion
(Ca2+) entered into secretary cells and achieved by the fusion of secretory vesicles with the plasma membrane. Recent accumulating
evidence has indicated that members of the synaptotagmin (Syt) family play a major role in Ca2+-dependent exocytosis, and Syt I, in particular, is now widely accepted as the major Ca2+-sensor for synchronous neurotransmitter release. Involvement of other Syt isoforms in Ca2+-dependent exocytotic events other than neurotransmitter release has also been reported, and the Syt IV isoform is of particular
interest, because Syt IV has several unique features not found in Syt I (e.g., immediate early gene product induced by deporalization
and postsynaptic localization). In this article, we summarize the literature on the multi-functional role of Syt IV in Ca2+-dependent exocytosis. 相似文献
2.
Zhen Zhang Enfu Hui Edwin R. Chapman Meyer B. Jackson 《Molecular biology of the cell》2009,20(24):5086-5095
The synaptic vesicle protein synaptotagmin I (Syt I) binds phosphatidylserine (PS) in a Ca2+-dependent manner. This interaction is thought to play a role in exocytosis, but its precise functions remain unclear. To determine potential roles for Syt I-PS binding, we varied the PS content in PC12 cells and liposomes and studied the effects on the kinetics of exocytosis and Syt I binding in parallel. Raising PS produced a steeply nonlinear, saturating increase in Ca2+-triggered fusion, and a graded slowing of the rate of fusion pore dilation. Ca2+-Syt I bound liposomes more tightly as PS content was raised, with a steep increase in binding at low PS, and a further gradual increase at higher PS. These two phases in the PS dependence of Ca2+-dependent Syt I binding to lipid may correspond to the two distinct and opposing kinetic effects of PS on exocytosis. PS influences exocytosis in two ways, enhancing an early step leading to fusion pore opening, and slowing a later step when fusion pores dilate. The possible relevance of these results to Ca2+-triggered Syt I binding is discussed along with other possible roles of PS. 相似文献
3.
Zhu D Zhou W Liang T Yang F Zhang RY Wu ZX Xu T 《Biochemical and biophysical research communications》2007,361(4):922-927
Synaptotagmins (Syts) constitute a large family of at least 16 members and individual Syt isoforms exhibit distinct Ca2+-binding properties and subcellular localization. It remains to be demonstrated whether multiple Syt isoforms can function independently or cooperatively on certain type of vesicle. In the current study, we have developed NPY-pHluorin to specifically assess exocytosis of large dense core vesicles (LDCVs) and studied the requirement of Syt I and Syt IX for LDCV exocytosis in PC12 cells. We found that down-regulation of both Syt I and Syt IX resulted in a significant loss of Ca2+-dependent LDCV exocytosis. Moreover, our results suggest Syt I and Syt IX play redundant role in controlling the choice of fusion modes. Down-regulation of both Syt I and Syt IX renders more fusion in the kiss-and-run mode. We conclude that Syt I and Syt IX function redundantly in Ca2+-sensing and fusion pore dilation on LDCVs in PC12 cells. 相似文献
4.
Hu ZT Chen MR Ping Z Dong YM Zhang RY Xu T Wu ZX 《Biochemical and biophysical research communications》2008,371(4):781-786
Synaptotagmins (Syts) are calcium-binding proteins which are conserved from nematodes to humans. Fifteen Syts have been identified in mammalian species. Syt I is recognized as a Ca2+ sensor for the synchronized release of synaptic vesicles in some types of neurons, but its role in the secretion of dense core vesicles (DCVs) remains unclear. The function of Syt IV is of particular interest because it is rapidly up-regulated by chronic depolarization and seizures. Using RNAi-mediated gene silencing, we have explored the role of Syt I and IV on secretion in a pituitary gonadotrope cell line. Downregulation of Syt IV clearly reduced Ca2+-triggered exocytosis of dense core vesicles (DCVs) in LβT2 cells. Syt I silencing, however, had no effect on vesicular release. 相似文献
5.
Regulation of exocytosis by purinergic receptors in pancreatic duct epithelial cells 总被引:2,自引:0,他引:2
Jung SR Kim MH Hille B Nguyen TD Koh DS 《American journal of physiology. Cell physiology》2004,286(3):C573-C579
In epithelial cells, several intracellular signals regulate the secretion of large molecules such as mucin via exocytosis and the transport of ions through channels and transporters. Using carbon fiber amperometry, we previously reported that exocytosis of secretory granules in dog pancreatic duct epithelial cells (PDEC) can be stimulated by pharmacological activation of cAMP-dependent protein kinase (PKA) or protein kinase C (PKC), as well as by an increase of intracellular free Ca2+ concentration ([Ca2+]i). In this study, we examined whether exocytosis in these cells is modulated by activation of endogenous P2Y receptors, which increase cAMP and [Ca2+]i. Low concentrations of ATP (<10 µM) induced intracellular Ca2+ oscillation but no significant exocytosis. In contrast, 100 µM ATP induced a sustained [Ca2+]i rise and increased the exocytosis rate sevenfold. The contribution of Ca2+ or cAMP pathways to exocytosis was tested by using the Ca2+ chelator BAPTA or the PKA inhibitors H-89 or Rp-8-bromoadenosine 3',5'-cyclic monophosphorothioate. Removal of [Ca2+]i rise or inhibition of PKA each partially reduced exocytosis; when combined, they abolished exocytosis. In conclusion, ATP at concentrations >10 µM stimulates exocytosis from PDEC through both Ca2+ and cAMP pathways. secretion; amperometry; photometry; calcium, adenosine 3',5'-cyclic monophosphate 相似文献
6.
Lei Li Haowen Liu Mia Krout Janet E. Richmond Yu Wang Jihong Bai Saroja Weeratunga Brett M. Collins Donovan Ventimiglia Yi Yu Jingyao Xia Jing Tang Jie Liu Zhitao Hu 《The Journal of cell biology》2021,220(4)
Ca2+-dependent neurotransmitter release requires synaptotagmins as Ca2+ sensors to trigger synaptic vesicle (SV) exocytosis via binding of their tandem C2 domains—C2A and C2B—to Ca2+. We have previously demonstrated that SNT-1, a mouse synaptotagmin-1 (Syt1) homologue, functions as the fast Ca2+ sensor in Caenorhabditis elegans. Here, we report a new Ca2+ sensor, SNT-3, which triggers delayed Ca2+-dependent neurotransmitter release. snt-1;snt-3 double mutants abolish evoked synaptic transmission, demonstrating that C. elegans NMJs use a dual Ca2+ sensor system. SNT-3 possesses canonical aspartate residues in both C2 domains, but lacks an N-terminal transmembrane (TM) domain. Biochemical evidence demonstrates that SNT-3 binds both Ca2+ and the plasma membrane. Functional analysis shows that SNT-3 is activated when SNT-1 function is impaired, triggering SV release that is loosely coupled to Ca2+ entry. Compared with SNT-1, which is tethered to SVs, SNT-3 is not associated with SV. Eliminating the SV tethering of SNT-1 by removing the TM domain or the whole N terminus rescues fast release kinetics, demonstrating that cytoplasmic SNT-1 is still functional and triggers fast neurotransmitter release, but also exhibits decreased evoked amplitude and release probability. These results suggest that the fast and slow properties of SV release are determined by the intrinsically different C2 domains in SNT-1 and SNT-3, rather than their N-termini–mediated membrane tethering. Our findings therefore reveal a novel dual Ca2+ sensor system in C. elegans and provide significant insights into Ca2+-regulated exocytosis. 相似文献
7.
Mari Nojiri Kelly M. Loyet Vadim A. Klenchin Gregory Kabachinski Thomas F. J. Martin 《The Journal of biological chemistry》2009,284(28):18707-18714
CAPS (Ca2+-dependent activator protein for secretion) functions in priming Ca2+-dependent vesicle exocytosis, but the regulation of CAPS activity has not been characterized. Here we show that phosphorylation by protein kinase CK2 is required for CAPS activity. Dephosphorylation eliminated CAPS activity in reconstituting Ca2+-dependent vesicle exocytosis in permeable and intact PC12 cells. Ser-5, -6, and -7 and Ser-1281 were identified by mass spectrometry as the major phosphorylation sites in the 1289 residue protein. Ser-5, -6, and -7 but not Ser-1281 to Ala substitutions abolished CAPS activity. Protein kinase CK2 phosphorylated CAPS in vitro at these sites and restored the activity of dephosphorylated CAPS. CK2 is the likely in vivo CAPS protein kinase based on inhibition of phosphorylation by tetrabromo-2-benzotriazole in PC12 cells and by the identity of in vivo and in vitro phosphorylation sites. CAPS phosphorylation by CK2 was constitutive, but the elevation of Ca2+ in synaptosomes increased CAPS Ser-5 and -6 dephosphorylation, which terminates CAPS activity. These results identify a functionally important N-terminal phosphorylation site that regulates CAPS activity in priming vesicle exocytosis.Regulated neurotransmitter secretion is central to intercellular communication in the nervous system. Two types of secretory vesicles mediate neurotransmitter release; that is, synaptic vesicles that release transmitters such as glutamate at synapses and dense-core vesicles that release modulatory transmitters and neuropeptides at non-synaptic sites. Both types of secretory vesicles are recruited to docking sites on the plasma membrane where they are primed to a ready release state to undergo fusion in response to Ca2+ elevations. Many of the proteins that mediate the targeting, docking, priming, and Ca2+-dependent fusion of vesicles with the plasma membrane function in both synaptic vesicle and dense-core vesicle pathways (1). CAPS-12 (also known as Cadps1) is a 1289-residue protein that reconstitutes Ca2+-triggered dense-core vesicle exocytosis in permeable neuroendocrine cells at a priming step (2–4). CAPS is required for secretion of a subset of transmitters in Caenorhabditis elegans (5) and Drosophila melanogaster (6) and for priming dense-core vesicle exocytosis in neuroendocrine cells (7) and synaptic vesicle exocytosis in neurons (8). Vesicle priming reactions are extensively modulated during physiological demand (9), but mechanisms that regulate CAPS function remain to be identified.Reversible protein phosphorylation is a major mechanism for the regulation of cellular processes including vesicle exocytosis. Many proteins that function in evoked vesicle exocytosis are phosphoproteins (10, 11). The neuronal SNARE proteins syntaxin 1A, VAMP-2, and SNAP-25 are phosphorylated by several protein kinases in vitro (12–14). Protein kinase C and protein kinase A sites on SNAP-25 affect refilling rates and size, respectively, of the primed pool of vesicles in chromaffin cells (15, 16). Several SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor)-binding proteins such as munc18, RIM1, and rabphilin undergo regulated phosphorylation, but it is not known whether phosphorylation affects function (10, 11, 17).Because the function of CAPS at a priming step in vesicle exocytosis may be regulated, we determined whether CAPS is phosphorylated. We show that CAPS is a phosphoprotein with functionally essential N-terminal phosphorylated Ser residues. Ser-5, -6, and -7 in CAPS were substrates for protein kinase CK2 in vitro and in vivo as well as for a Ca2+-dependent dephosphorylation mechanism. The results indicate that phosphorylation by protein kinase CK2 is necessary for CAPS activity in priming vesicle exocytosis and that regulated dephosphorylation may constitute a mechanism for terminating CAPS activity. 相似文献
8.
Ca2+ and protein kinase C activation of mucin granule exocytosis in permeabilized SPOC1 cells 总被引:2,自引:0,他引:2
Scott C. E.; Abdullah Lubna H.; Davis C. William 《American journal of physiology. Cell physiology》1998,275(1):C285
Mucin secretion by airway goblet cells is under the control ofapical P2Y2, phospholipaseC-coupled purinergic receptors. In SPOC1 cells, the mobilization ofintracellular Ca2+ by ionomycin orthe activation of protein kinase C (PKC) by phorbol 12-myristate13-acetate (PMA) stimulates mucin secretion in a fully additive fashion[L. H. Abdullah, J. D. Conway, J. A. Cohn, and C. W. Davis.Am. J. Physiol. 273 (Lung Cell. Mol. Physiol. 17):L201-L210, 1997]. This apparent independence between PKC andCa2+ in the stimulation of mucinsecretion was tested in streptolysin O-permeabilized SPOC1 cells. Thesecells were fully competent to secrete mucin whenCa2+ was elevated from 100 nM to3.1 µM for 2 min following permeabilization; theCa2+EC50 was 2.29 ± 0.07 µM.Permeabilized SPOC1 cells were exposed to PMA or 4-phorbol atCa2+ activities ranging from 10 nMto 10 µM. PMA, but not 4-phorbol, increased mucin release at allCa2+ activities tested: at 10 nMCa2+ mucin release was 2.1-foldgreater than control and at 4.7 µM Ca2+ mucin release was maximal(3.6-fold increase). PMA stimulated 27% more mucin release at 4.7 µMthan at 10 nM Ca2+. Hence, SPOC1cells possess Ca2+-insensitive,PKC-dependent, and Ca2+-dependentPKC-potentiated pathways for mucin granule exocytosis. 相似文献
9.
Greg Kabachinski Masaki Yamaga D. Michelle Kielar-Grevstad Stephen Bruinsma Thomas F. J. Martin 《Molecular biology of the cell》2014,25(4):508-521
Phosphoinositides provide compartment-specific signals for membrane trafficking. Plasma membrane phosphatidylinositol 4,5-bisphosphate (PIP2) is required for Ca2+-triggered vesicle exocytosis, but whether vesicles fuse into PIP2-rich membrane domains in live cells and whether PIP2 is metabolized during Ca2+-triggered fusion were unknown. Ca2+-dependent activator protein in secretion 1 (CAPS-1; CADPS/UNC31) and ubMunc13-2 (UNC13B) are PIP2-binding proteins required for Ca2+-triggered vesicle exocytosis in neuroendocrine PC12 cells. These proteins are likely effectors for PIP2, but their localization during exocytosis had not been determined. Using total internal reflection fluorescence microscopy in live cells, we identify PIP2-rich membrane domains at sites of vesicle fusion. CAPS is found to reside on vesicles but depends on plasma membrane PIP2 for its activity. Munc13 is cytoplasmic, but Ca2+-dependent translocation to PIP2-rich plasma membrane domains is required for its activity. The results reveal that vesicle fusion into PIP2-rich membrane domains is facilitated by sequential PIP2-dependent activation of CAPS and PIP2-dependent recruitment of Munc13. PIP2 hydrolysis only occurs under strong Ca2+ influx conditions sufficient to activate phospholipase Cη2 (PLCη2). Such conditions reduce CAPS activity and enhance Munc13 activity, establishing PLCη2 as a Ca2+-dependent modulator of exocytosis. These studies provide a direct view of the spatial distribution of PIP2 linked to vesicle exocytosis via regulation of lipid-dependent protein effectors CAPS and Munc13. 相似文献
10.
Prinz Christian; Zanner Robert; Gerhard Markus; Mahr Sabine; Neumayer Nina; Hohne-Zell Barbara; Gratzl Manfred 《American journal of physiology. Cell physiology》1999,277(5):C845
Enterochromaffin-like (ECL) cells play a pivotal role in theperipheral regulation of gastric acid secretion as they respond to thefunctionally important gastrointestinal hormones gastrin andsomatostatin and neural mediators such as pituitary adenylate cyclase-activating peptide and galanin. Gastrin is the keystimulus of histamine release from ECL cells in vivo and in vitro.Voltage-gated K+ andCa2+ channels have been detectedon isolated ECL cells. Exocytosis of histamine following gastrinstimulation and Ca2+ entry acrossthe plasma membrane is catalyzed by synaptobrevin andsynaptosomal-associated protein of 25 kDa, both characterized as asoluble N-ethylmaleimide-sensitivefactor attachment protein receptor protein. Histamine release occursfrom different cellular pools: preexisting vacuolar histamineimmediately released by Ca2+ entryor newly synthesized histamine following induction of histidine decarboxylase (HDC) by gastrin stimulation. Histamine is synthesized bycytoplasmic HDC and accumulated in secretory vesicles byproton-histamine countertransport via the vesicular monoaminetransporter subtype 2 (VMAT-2). The promoter region of HDC containsCa2+-, cAMP-, and protein kinaseC-responsive elements. The gene promoter for VMAT-2, however, lacksTATA boxes but contains regulatory elements for the hormones glucagonand somatostatin. Histamine secretion from ECL cells is thereby under acomplex regulation of hormonal signals and can be targeted at severalsteps during the process of exocytosis. 相似文献
11.
Zhen Zhang Enfu Hui Edwin R. Chapman Meyer B. Jackson 《Molecular biology of the cell》2010,21(16):2821-2831
Synaptotagmin (syt) serves as a Ca2+ sensor in the release of neurotransmitters and hormones. This function depends on the ability of syt to interact with other molecules. Syt binds to phosphatidylserine (PS)-containing lipid bilayers as well as to soluble N-ethylmaleimide sensitive factor receptors (SNAREs) and promotes SNARE assembly. All these interactions are regulated by Ca2+, but their specific roles in distinct kinetic steps of exocytosis are not well understood. To explore these questions we used amperometry recording from PC12 cells to investigate the kinetics of exocytosis. Syt isoforms and syt I mutants were overexpressed to perturb syt-PS and syt-SNARE interactions to varying degrees and evaluate the effects on fusion event frequency and the rates of fusion pore transitions. Syt I produced more rapid dilation of fusion pores than syt VII or syt IX, consistent with its role in synchronous synaptic release. Stronger syt-PS interactions were accompanied by a higher frequency of fusion events and more stable fusion pores. By contrast, syt-SNARE interactions and syt-induced SNARE assembly were uncorrelated with rates of exocytosis. This associates the syt-PS interaction with two distinct kinetic steps in Ca2+ triggered exocytosis and supports a role for the syt-PS interaction in stabilizing open fusion pores. 相似文献
12.
Adams KL Maxson MM Mellander L Westerink RH Ewing AG 《Cellular and molecular neurobiology》2010,30(8):1235-1242
Fast neuromodulatory effects of 17-β-estradiol (E2) on cytosolic calcium concentration ([Ca2+]
i
) have been reported in many cell types, but little is known about its direct effects on vesicular neurotransmitter secretion
(exocytosis). We examined the effects of E2 on depolarization-evoked [Ca2+]
i
in PC12 cells using fluorescence measurements. Imaging of [Ca2+]
i
with FURA-2 revealed that depolarization-evoked calcium entry is inhibited after exposure to 10 nM and 10 μM E2. Calcium
entry after exposure to 50 μM E2 decreases slightly, but insignificantly. To relate E2-induced changes in [Ca2+]
i
to functional effects, we measured exocytosis using amperometry. It was observed that E2 in some cells elicits exocytosis
upon exposure. In addition, E2 inhibits depolarization-evoked exocytosis with a complex concentration dependence, with inhibition
at both physiological and pharmacological concentrations. This rapid inhibition amounts to 45% at a near physiological level
(10 nM E2), and 50% at a possible pharmacological concentration of 50 μM. A small percentage (22%) of cells show exocytosis
during E2 exposure (“Estrogen stimulated”), thus vesicle depletion could possibly account (at least partly) for the E2-induced
inhibition of depolarization-evoked exocytosis. In cells that do not exhibit E2-stimulated release (“Estrogen quiet”), the
E2-induced inhibition of exocytosis is abolished by a treatment that eliminates the contribution of N-type voltage-gated calcium
channels (VGCCs) to exocytosis. Overall, the data suggest that E2 can act on N-type VGCCs to affect secretion of neurotransmitters.
This provides an additional mechanism for the modulation of neuronal communication and plasticity by steroids. 相似文献
13.
Ikebuchi Yoshihide; Masumoto Nobuyuki; Matsuoka Tetsu; Yokoi Takeshi; Tahara Masahiro; Tasaka Keiichi; Miyake Akira; Murata Yuji 《American journal of physiology. Cell physiology》1998,274(6):C1496
Synaptosome-associated protein of 25 kDa (SNAP-25) has beenshown to play an important role inCa2+-dependent exocytosis inneurons and endocrine cells. During fertilization, sperm-egg fusioninduces cytosolic Ca2+mobilization and subsequentlyCa2+-dependent cortical granule(CG) exocytosis in eggs. However, it is not yet clear whether SNAP-25is involved in this process. In this study, we determined theexpression and function of SNAP-25 in mouse eggs. mRNA and SNAP-25 weredetected in metaphase II (MII) mouse eggs by RT-PCR and immunoblotanalysis, respectively. Next, to determine the function of SNAP-25, weevaluated the change in CG exocytosis with a membrane dye,tetramethylammonium-1,6-diphenyl-1,3,5-hexatriene, after microinjectionof a botulinum neurotoxin A (BoNT/A), which selectively cleaves SNAP-25in MII eggs. Sperm-induced CG exocytosis was significantly inhibited inthe BoNT/A-treated eggs. The inhibition was attenuated by coinjectionof SNAP-25. These results suggest that SNAP-25 may be involved inCa2+-dependent CG exocytosisduring fertilization in mouse eggs. 相似文献
14.
Greg Kabachinski D. Michelle Kielar-Grevstad Xingmin Zhang Declan J. James Thomas F. J. Martin 《Molecular biology of the cell》2016,27(4):654-668
The Ca2+-dependent exocytosis of dense-core vesicles in neuroendocrine cells requires a priming step during which SNARE protein complexes assemble. CAPS (aka CADPS) is one of several factors required for vesicle priming; however, the localization and dynamics of CAPS at sites of exocytosis in live neuroendocrine cells has not been determined. We imaged CAPS before, during, and after single-vesicle fusion events in PC12 cells by TIRF microscopy. In addition to being a resident on cytoplasmic dense-core vesicles, CAPS was present in clusters of approximately nine molecules near the plasma membrane that corresponded to docked/tethered vesicles. CAPS accompanied vesicles to the plasma membrane and was present at all vesicle exocytic events. The knockdown of CAPS by shRNA eliminated the VAMP-2–dependent docking and evoked exocytosis of fusion-competent vesicles. A CAPS(ΔC135) protein that does not localize to vesicles failed to rescue vesicle docking and evoked exocytosis in CAPS-depleted cells, showing that CAPS residence on vesicles is essential. Our results indicate that dense-core vesicles carry CAPS to sites of exocytosis, where CAPS promotes vesicle docking and fusion competence, probably by initiating SNARE complex assembly. 相似文献
15.
Moore JM Papke JB Cahill AL Harkins AB 《American journal of physiology. Cell physiology》2006,291(2):C270-C281
Synaptotagmin (syt) I is a Ca2+-binding protein that is well accepted as a major sensor for Ca2+-regulated release of transmitter. However, controversy remains as to whether syt I is the only protein that can function in this role and whether the remaining syt family members also function as Ca2+ sensors. In this study, we generated a PC12 cell line that continuously expresses a short hairpin RNA (shRNA) to silence expression of syt I by RNA interference. Immunoblot and immunocytochemistry experiments demonstrate that expression of syt I was specifically silenced in cells that stably integrate the shRNA-syt I compared with control cells stably transfected with the empty shRNA vector. The other predominantly expressed syt isoform, syt IX, was not affected, nor was the expression of the SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) proteins when syt I levels were knocked down. Resting Ca2+ and stimulated Ca2+ influx imaged with fura-2 were not altered in syt I knockdown cells. However, evoked release of catecholamine detected by carbon fiber amperometry and HPLC was significantly reduced, although not abolished. Human syt I rescued the release events in the syt I knockdown cells. The reduction of stimulated catecholamine release in the syt I knockdown cells strongly suggests that although syt I is clearly involved in catecholamine release, it is not the only protein to regulate stimulated release in PC12 cells, and another protein likely has a role as a Ca2+ sensor for regulated release of transmitter. RNA interference; amperometry; exocytosis 相似文献
16.
The effect of a protein kinase inhibitor, staurosporine, on Ca2+-dependent and Ca2+-independent release of [14C]GABA in isolated rat brain synaptosomes was studied. Calcium-dependent [14C]GABA release was stimulated by depolarization with a K+ channel blocker, 4-aminopyridine (4-AP), or high K+ concentration. It has been shown that the effect of 4-AP is Ca2+-dependent, while high K+ is able to evoke [14C]GABA release in both Ca2+-dependent and Ca2+-independent manners. In addition, Ca2+-independent [14C]GABA release was studied using α-latrotoxin (LTX) as a tool. Pretreatment of synaptosomes with staurosporine resulted in
pronounced inhibition of 4-AP-stimulated Ca2+-dependent [14C]GABA release. The inhibitory effect of staurosporine on [14C]GABA release was not due to modulation of 4-AP-promoted45Ca2+ influx into synaptosomes. If the process of [14C]GABA release occurred in the Ca2+-independent manner irrespectively of what, LTX or high K+, stimulated this process, it was not inhibited by staurosporine. Considering the above findings, it is reasonable to assume
that the absence of Ca2+ in the extracellular medium created conditions for activation of the process of neurotransmitter release without Ca2+-dependent dephosphorylation of neuronal phosphoproteins; as a consequence, regulation of exocytotic process was modulated
in such a manner that inhibition of protein kinases did not disturb exocytosis. 相似文献
17.
Palmer Bradley M.; Lynch Joshua M.; Snyder Steven M.; Moore Russell L. 《Journal of applied physiology》1999,86(2):584-591
The effects ofendurance run training onNa+-dependentCa2+ regulation in rat leftventricular myocytes were examined. Myocytes were isolated fromsedentary and trained rats and loaded with fura 2. Contractile dynamicsand fluorescence ratio transients were recorded during electricalpacing at 0.5 Hz, 2 mM extracellular Ca2+ concentration, and 29°C.Resting and peak cytosolic Ca2+concentration([Ca2+]c)did not change with exercise training. However, resting and peak[Ca2+]cincreased significantly in both groups during 5 min of continuous pacing, although diastolic[Ca2+]cin the trained group was less susceptible to this elevation ofintracellular Ca2+. Run trainingalso significantly reduced the rate of[Ca2+]cdecay during relaxation. Myocytes were then exposed to 10 mM caffeinein the absence of external Na+ orCa2+ to trigger sarcoplasmicreticular Ca2+ release and tosuppress cellular Ca2+ efflux.This maneuver elicited an elevated steady-state[Ca2+]c.External Na+ was then added, andthe rate of[Ca2+]cclearance was determined. Run training significantly reduced the rateof Na+-dependent clearance of[Ca2+]cduring the caffeine-induced contractures. These data demonstrate thatthe removal of cytosolic Ca2+ wasdepressed with exercise training under these experimental conditionsand may be specifically reflective of a training-induced decrease inthe rate of cytosolic Ca2+ removalviaNa+/Ca2+exchange and/or in the amount ofCa2+ moved across the sarcolemmaduring a contraction. 相似文献
18.
Cyclic ADP-ribose activates caffeine-sensitive calcium channels from sea urchin egg microsomes 总被引:1,自引:0,他引:1
Perez Claudio F.; Marengo Juan Jose; Bull Ricardo; Hidalgo Cecilia 《American journal of physiology. Cell physiology》1998,274(2):C430
Adenosine 5'-cyclic diphosphoribose [cyclicADP-ribose (cADPR)], a metabolite ofNAD+ that promotesCa2+ release from sea urchin egghomogenates and microsomal fractions, has been proposed to act as anendogenous agonist of Ca2+ releasein sea urchin eggs. We describe experiments showing that a microsomalfraction isolated from Tetrapigusnyger sea urchin eggs displayedCa2+-selective single channelswith conductances of 155.0 ± 8.0 pS in asymmetricCs+ solutions and 47.5 ± 1.1 pS in asymmetric Ca2+ solutions.These channels were sensitive to stimulation byCa2+, ATP, and caffeine, but notinositol 1,4,5-trisphosphate, and were inhibited by ruthenium red. Thechannels were also activated by cADP-ribose in aCa2+-dependent fashion. Calmodulinand Mg2+, but not heparin,modulated channel activity in the presence of cADP-ribose. We proposethat these Ca2+ channelsconstitute the intracellularCa2+-inducedCa2+ release pathway that isactivated by cADP-ribose in sea urchin eggs. 相似文献
19.
Synaptotagmin-2 Controls Regulated Exocytosis but Not Other Secretory Responses of Mast Cells 总被引:1,自引:0,他引:1
Ernestina Melicoff Leticia Sansores-Garcia Alejandra Gomez Daniel C. Moreira Proleta Datta Pratima Thakur Youlia Petrova Tanya Siddiqi Jayasimha N. Murthy Burton F. Dickey Ruth Heidelberger Roberto Adachi 《The Journal of biological chemistry》2009,284(29):19445-19451
20.
Noll T Schäfer M Schavier-Schmitz U Piper HM 《American journal of physiology. Cell physiology》2000,279(3):C717-C723
In cultured porcine aortic endothelial monolayers, theeffect of ATP on myosin light chain (MLC) phosphorylation, whichcontrols the endothelial contractile machinery, was studied. ATP (10 µM) reduced MLC phosphorylation but increased cytosolicCa2+ concentration ([Ca2+]i).Inhibition of the ATP-evoked [Ca2+]i rise byxestospongin C (10 µM), an inhibitor of the inositol trisphosphate-dependent Ca2+ release from endoplasmicreticulum, did not affect the ATP-induced dephosphorylation of MLC. MLCdephosphorylation was prevented in the presence of calyculin A (10 nM),an inhibitor of protein phosphatases PP-1 and PP-2A. Thus ATP activatesMLC dephosphorylation in a Ca2+-independent manner. In thepresence of calyculin A, MLC phosphorylation was incremented afteraddition of ATP, an effect that could be abolished when cellswere loaded with the Ca2+ chelator1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acidacetoxymethyl ester (10 µM). Thus ATP also activates aCa2+-dependent kinase acting on MLC. In summary, ATPsimultaneously stimulates a functional antagonism toward bothphosphorylation and dephosphorylation of MLC in which thedephosphorylation prevails. In endothelial cells, ATP is the firstphysiological mediator identified to activate MLC dephosphorylation bya Ca2+-independent mechanism. 相似文献