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1.
The basic mechanisms of regulation of Ca2+ influx have been studied in murine myoblasts proliferating and differentiating in culture. The presence of L-type Ca2+ channels in proliferating myoblasts is shown for the first time. It is also shown that the influx of Ca2+ through these channels is regulated by the adrenergic system. The influx of Ca2+ after activation of the adrenergic system by addition of adrenaline has been estimated in comparison with the contribution of reticular stocks exhausted by ATP in calcium-free medium. The Ca2+ influx in proliferating myoblasts is regulated by β-2 adrenergic receptors whose action is mediated by adenylate cyclase through L-type calcium channels. In differentiating myoblasts, the adrenaline-induced Ca2+ influx is substantially lower than in proliferating cells, and maximal influx of Ca2+ may be reached only upon exhaustion of reticular stocks.  相似文献   

2.
Using Fura-2AM microfluorimetry, it was shown for the first time that neuroleptic chlorpromazine causes intracellular Ca2+ concentration increase in macrophages due to Ca2+ mobilization from intracellular Ca2+ stores and subsequent Ca2+ entry from the external medium. Chlorpromazine-induced Ca2+ entry is inhibited by La3+ and 2-aminoethoxydiphenyl borate and is associated with Ca2+ store depletion.  相似文献   

3.
We studied store-dependent (activated by depletion of the endoplasmic reticulum, ER, store) entry of Ca2+ from the extracellular medium into neurons of the rat spinal ganglia (small- and medium-sized cells; diameter, 18 to 36 μm). Activation of ryanodine-sensitive receptors of the ER in the studied neurons superfused by Tyrode solutions containing Ca2+ or with no Ca2+ was provided by application of 10 mM caffeine. The decay phase of caffeine-induced calcium transients in a Ca2+-containing solution was significantly longer than that in a Ca2+-free solution. This fact allows us to suppose that such a phenomenon is determined by Ca2+ entry into the neuron from the extracellular medium activated by caffeine-induced depletion of the ER store. Substitution of Ca2+-free extracellular solution by Ca2+-containing Tyrode solution, after depletion of the ER stores induced by applications of 100 nM ryanodine, 200 μM ATP, or 1 μM thapsigargin, resulted in increases in the concentration of intracellular Ca2+. These observations allow us to postulate that store-dependent Ca2+ entry into the studied neurons is activated after depletion not only of the inositol trisphosphate-sensitive ER store but also of the ryanodine-sensitive store. This entry also occurs after blocking of ATPases of the ER by thapsigargin. The kinetic characteristics of the rising phase of store-dependent Ca2+ entry induced by depletion of the ER stores under the influence of various agents are dissimilar; this can be related to different mechanisms of activation of such signals and/or to a compartmental organization of the ER. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 277–283, May–June, 2005.  相似文献   

4.
Phosphorylation of the cardiac ryanodine receptor (RyR2) is thought to be important not only for normal cardiac excitation-contraction coupling but also in exacerbating abnormalities in Ca2+ homeostasis in heart failure. Linking phosphorylation to specific changes in the single-channel function of RyR2 has proved very difficult, yielding much controversy within the field. We therefore investigated the mechanistic changes that take place at the single-channel level after phosphorylating RyR2 and, in particular, the idea that PKA-dependent phosphorylation increases RyR2 sensitivity to cytosolic Ca2+. We show that hyperphosphorylation by exogenous PKA increases open probability (P o) but, crucially, RyR2 becomes uncoupled from the influence of cytosolic Ca2+; lowering [Ca2+] to subactivating levels no longer closes the channels. Phosphatase (PP1) treatment reverses these gating changes, returning the channels to a Ca2+-sensitive mode of gating. We additionally found that cytosolic incubation with Mg2+/ATP in the absence of exogenously added kinase could phosphorylate RyR2 in approximately 50% of channels, thereby indicating that an endogenous kinase incorporates into the bilayer together with RyR2. Channels activated by the endogenous kinase exhibited identical changes in gating behavior to those activated by exogenous PKA, including uncoupling from the influence of cytosolic Ca2+. We show that the endogenous kinase is both Ca2+-dependent and sensitive to inhibitors of PKC. Moreover, the Ca2+-dependent, endogenous kinase–induced changes in RyR2 gating do not appear to be related to phosphorylation of serine-2809. Further work is required to investigate the identity and physiological role of this Ca2+-dependent endogenous kinase that can uncouple RyR2 gating from direct cytosolic Ca2+ regulation.  相似文献   

5.
Much less attention has been paid to Zn2+ in artificial cerebrospinal fluid (ACSF), i.e., extracellular medium, used for in vitro slice experiments than divalent cations such as Ca2+. Approximately 2 mM Ca2+ is added to conventional ACSF from essentiality of Ca2+ signaling in neurons and glial cells. However, no Zn2+ is added to it, even though the importance of Zn2+ signaling in them is recognizing. On the other hand, synaptic Zn2+ homeostasis is changed during brain slice preparation. Therefore, it is possible that not only neuronal excitation but also synaptic plasticity such as long-term potentiation is modified in ACSF without Zn2+, in which original physiology might not appear. The basal (static) levels of intracellular (cytosolic) Zn2+ and Ca2+ are not significantly different between brain slices prepared with conventional ACSF without Zn2+ and pretreated with ACSF containing 20 nM ZnCl2 for 1 h. In the case of mossy fiber excitation, however, presynaptic activity assessed with FM 4–64 is significantly suppressed in the stratum lucidum of brain slices pretreated with ACSF containing Zn2+, indicating that hippocampal excitability is enhanced in brain slices prepared with ACSF without Zn2+. The evidence suggests that low nanomolar concentration of Zn2+ is necessary for ACSF. Furthermore, exogenous Zn2+ has opposite effect on LTP induction between in vitro and in vivo experiments. It is required to pay attention to extracellular Zn2+ concentration to understand synaptic function precisely.  相似文献   

6.
Our understanding of vascular endothelial cell physiology is based on studies of endothelial cells cultured from various vascular beds of different species for varying periods of time. Systematic analysis of the properties of endothelial cells from different parts of the vasculature is lacking. Here, we compare Ca2+ homeostasis in primary cultures of endothelial cells from human internal mammary artery and saphenous vein and how this is modified by hypoxia, an inevitable consequence of bypass grafting (2.5% O2, 24 h). Basal [Ca2+] i and store depletion-mediated Ca2+ entry were significantly different between the two cell types, yet agonist (ATP)–mediated mobilization from endoplasmic reticulum stores was similar. Hypoxia potentiated agonist-evoked responses in arterial, but not venous, cells but augmented store depletion-mediated Ca2+ entry only in venous cells. Clearly, Ca2+ signaling and its remodeling by hypoxia are strikingly different in arterial vs. venous endothelial cells. Our data have important implications for the interpretation of data obtained from endothelial cells of varying sources.  相似文献   

7.
Calcium signaling is a key regulator of processes important in differentiation. In colon cancer cells differentiation is associated with altered expression of specific isoforms of calcium pumps of the endoplasmic reticulum and the plasma membrane, suggesting that differentiation of colon cancer cells is associated with a major remodeling of calcium homeostasis. Purinergic and neurotensin receptor activation are known regulators of cytosolic free Ca2+ levels in colon cancer cells. This study aimed to assess changes in cytosolic free Ca2+ levels in response to ATP and neurotensin with differentiation induced by sodium butyrate or culturing post-confluence. Parameters assessed included peak cytosolic free Ca2+ level after activation; time to reach peak cytosolic free Ca2+ and the EC50 of dose response curves. Our results demonstrate that differentiation of HT-29 colon cancer cells is associated with a remodeling of both ATP and neurotensin mediated Ca2+ signaling. Neurotensin-mediated calcium signaling appeared more sensitive to differentiation than ATP-mediated Ca2+ signaling.  相似文献   

8.
The characteristics and properties of the increase in cytosolic [Ca2+] that occurs in bovine adrenal medullary chromaffin cells on exposure to histamine have been investigated. Specifically, these experiments were conducted to determine how much external Ca2+ enters the cell through a (capacitative) Ca2+ entry pathway activated as a consequence of intracellular Ca2+ store mobilization, relative to that which enters independently of store depletion via other channels activated by histamine. In Fura-2 loaded cells continued exposure to histamine (10 μM) caused a rapid but transient increase in cytosolic [Ca2+] followed by a lower plateau that was sustained as long as external Ca2+ was present. In the absence of external Ca2+ only the initial brief transient was observed. In cells previously treated with thapsigargin (100 nM) in Ca2+-free medium to deplete the internal Ca2+ stores, histamine caused no increase in cytosolic [Ca2+] when external Ca2+ was absent. Re-introduction of external Ca2+ to thapsigargin-treated store-depleted cells caused a sustained increase in cytosolic [Ca2+] that was further increased (P < 0.0002) upon exposure to histamine. The histamine-evoked increase was prevented by the H1-receptor antagonist, mepyramine (2 μM). A comparison was made between store-dependent Ca2+ entry consequent upon store mobilization with histamine in Ca2+-free medium and plateau phase Ca2+ entry resulting from stimulation with histamine in Ca2+-containing medium. The latter was found to be approximately 3 times greater in magnitude than the former (P ? 0.0001) at the same concentration of histamine (10 μM). It is concluded that histamine causes Ca2+ entry not only via a capacitative entry pathway secondary to internal store mobilization, but also causes substantial Ca2+ entry through other pathways.  相似文献   

9.
The anoxia-dependent elevation of cytosolic Ca2+ concentration, [Ca2+]cyt, was investigated in plants differing in tolerance to hypoxia. The [Ca2+]cyt was measured by fluorescence microscopy in single protoplasts loaded with the calcium-fluoroprobe Fura 2-AM. Imposition of anoxia led to a fast (within 3 min) significant elevation of [Ca2+]cyt in rice leaf protoplasts. A tenfold drop in the external Ca2+ concentration (to 0.1 mM) resulted in considerable decrease of the [Ca2+]cyt shift. Rice root protoplasts reacted upon anoxia with higher amplitude. Addition of plasma membrane (verapamil, La3+ and EGTA) and intracellular membrane Ca2+-channel antagonists (Li+, ruthenium red and cyclosporine A) reduced the anoxic Ca2+-accumulation in rice. Wheat protoplasts responded to anoxia by smaller changes of [Ca2+]cyt. In wheat leaf protoplasts, the amplitude of the Ca2+-shift little depended on the external level of Ca2+. Wheat root protoplasts were characterized by a small shift of [Ca2+]cyt under anoxia. Plasmalemma Ca2+-channel blockers had little effect on the elevation of cytosolic Ca2+ in wheat protoplasts. Intact rice seedlings absorbed Ca2+ from the external medium under anoxic treatment. On the contrary, wheat seedlings were characterized by leakage of Ca2+. Verapamil abolished the Ca2+ influx in rice roots and Ca2+ efflux from wheat roots. Anoxia-induced [Ca2+]cyt elevation was high particularly in rice, a hypoxia-tolerant species. In conclusion, both external and internal Ca2+ stores are important for anoxic [Ca2+]cyt elevation in rice, whereas the hypoxia-intolerant wheat does not require external sources for [Ca2+]cyt rise. Leaf and root protoplasts similarly responded to anoxia, independent of their organ origin.  相似文献   

10.
Using Fura-2AM microfluorimetry, the effect of oxidized glutathione (GSSG) and its pharmacological analogue glutoxim on the intracellular Ca2+ concentration in rat peritoneal macrophages was investigated. It was shown that GSSG or glutoxim increase the intracellular Ca2+ concentration by inducing Ca2+ mobilization from thapsigargin-sensitive Ca2+ stores and subsequent Ca2+ entry from external medium. Dithiothreitol, which reduces S-S-bonds in proteins, completely prevents or reverses the increase of intracellular Ca2+ concentration induced by GSSG or glutoxim. This suggests that the increase of intracellular Ca2+ concentration induced by GSSG or glutoxim can be mediated by their interactions with functionally important SH-groups of proteins involved in Ca2+-signaling.Two structurally different tyrosine kinase inhibitors genistein and methyl-2,5-dihydroxycinnamate prevent or completely reverse the increase in the intracellular Ca2+ concentration induced by GSSG or glutoxim. On the contrary, tyrosine phosphatase inhibitor Na orthovanadate enhances the increase of intracellular Ca2+ concentration evoked by oxidizing agents. The data suggest that tyrosine kinases and tyrosine phosphatases are involved in the regulatory effect of GSSG and glutoxim on the intracellular Ca2+ concentration in macrophages.  相似文献   

11.
Synaptically activated postsynaptic [Ca2+]i increases occur through three main pathways: Ca2+ entry through voltage-gated Ca2+ channels, Ca2+ entry through ligand-gated channels, and Ca2+ release from internal stores. The first two pathways have been studied intensively; release from stores has been the subject of more recent investigations.Ca2+ release from stores in CNS neurons primarily occurs as a result of IP3 mobilized by activation of metabotropic glutamatergic and/or cholingergic receptors coupled to PLC. Ca2+ release is localized near spines in Purkinje cells and occurs as a wave in the primary apical dendrites of pyramidal cells in the hippocampus and cortex. The amplitude of the [Ca2+]i increase can reach several micromolar, significantly larger than the increase due to backpropagating spikes.The large amplitude, long duration, and unique location of the [Ca2+]i increases due to Ca2+ release from stores suggests that these increases can affect specific downstream signaling mechanisms in neurons.  相似文献   

12.
Fluorescence resonance energy transfer (FRET)-based protein biosensors allow the spatial and temporal imaging of signaling events in living cells. However, the simultaneous correlation of multiple events of a signaling pathway is hindered by the spectral cross-talk between fluorescent proteins. Here, we show, for signaling pathways that progress synchronously, multiple events can be correlated by using co-cultures expressing different FRET-based protein biosensors. As a demonstration, we investigated the simultaneous caspase-3 and Ca2+ signaling events involved in cell death of COS-7 cells induced by 10 mM H2O2. Interestingly, this H2O2 stimulus induced synchronous caspase-3 activation and Ca2+ signaling. In parallel to caspase-3 activation, cytosolic Ca2+ concentration, [Ca2+]c, gradually rises to its peak and then slowly drops. As cell shrinkage and rounding ensues, [Ca2+]c again gradually rises to its peak and then reaches a plateau. These observations reveal the relative timing and location of these signaling events in cell death induced by this stimulus of H2O2. Finally, our approach offers an exciting opportunity for spatial and temporal imaging of multiple events in a signaling pathway in living cells.  相似文献   

13.
Acinar cell exocytosis requires spatiotemporal Ca2+ signals regulated through endoplasmic reticulum (ER) stores, Ca2+ATPases, and store-operated Ca2+ entry (SOCE). The secretory pathway Ca2+ATPase 2 (SPCA2) interacts with Orai1, which is involved in SOCE and store independent Ca2+ entry (SICE). However, in the pancreas, only a C-terminally truncated form of SPCA2 (termed SPAC2C) exists. The goal of this study was to determine if SPCA2C effects Ca2+ homeostasis in a similar fashion to the full-length SPCA2.Using epitope-tagged SPCA2C (SPCA2CFLAG) expressed in HEK293A cells and Fura2 imaging, cytosolic [Ca2+] was examined during SICE, SOCE and secretagogue-stimulated signaling. Exogenous SPCA2C expression increased resting cytosolic [Ca2+], Ca2+ release in response to carbachol, ER Ca2+ stores, and store-mediated and independent Ca2+ influx. Co-IP detected Orai1-SPCA2C interaction, which was altered by co-expression of STIM1. Importantly, SPCA2C's effects on store-mediated Ca2+ entry were independent of Orai1. These findings indicate SPCA2C influences Ca2+ homeostasis through multiple mechanisms, some of which are independent of Orai1, suggesting novel and possibly cell-specific Ca2+ regulation.  相似文献   

14.
Among the scarce available data about the biological role of the membrane protein CD20, there is some evidence that this protein functions as a store-operated Ca2+ channel and/or regulates transmembrane Ca2+ trafficking. Recent findings indicate that store-operated Ca2+ entry (SOCE) plays a central role in skeletal muscle function and development, but there remain a number of unresolved issues relating to SOCE modulation in this tissue. Here we describe CD20 expression in skeletal muscle, verifying its membrane localization in myoblasts and adult muscle fibers. Additionally, we show that inhibition of CD20 through antibody binding or gene silencing resulted in specific impairment of SOCE in C2C12 myoblasts. Our results provide novel insights into the CD20 expression pattern, and suggest that functional CD20 is required for SOCE to consistently occur in C2C12 myoblasts. These findings may contribute to future identification of mechanisms and molecules involved in the fine regulation of store-operated Ca2+ entry in skeletal muscle.  相似文献   

15.
Nitric oxide (NO) plays an important role as an intra- and intercellular signaling molecule in mammalian tissues. In the submandibular gland, NO has been suggested to be involved in the regulation of secretion and in blood flow. NO is produced by activation of NO synthase (NOS). Here, we have investigated the regulation of NOS activity in the rabbit submandibular gland. NOS activity was detected in both the cytosolic and membrane fractions. Characteristics of NOS in the cytosolic and partially purified membrane fractions, such as Km values for l-arginine and EC50 values for calmodulin and Ca2+, were similar. A protein band that cross-reacted with anti-nNOS antibody was detected in both the cytosolic and membrane fractions. The membrane-fraction NOS activity increased 1.82-fold with treatment of Triton X-100, but the cytosolic-fraction NOS activity did not. The NOS activity was inhibited by phosphatidic acid (PA) and phosphatidylinositol 4,5-bisphosphate (PIP2). The inhibitory effects of phospholipids on the NOS activity were relieved by an increase in Ca2+ concentrations. These results suggest that the Ca2+- and calmodulin-regulating enzyme nNOS occurs in cytosolic and membrane fractions, and PA and PIP2 regulate the NOS activity in the membrane site by regulating the effect of Ca2+ in the rabbit submandibular gland.Communicated by I.D. Hume  相似文献   

16.
Intracellular calcium ([Ca2+]i) plays a pivotal role in neuronal ischemia. The aim of the present study was to investigate the routes of Ca2+ entry during non-excitotoxic oxygen and glucose deprivation (OGD) in acutely dissociated rat CA1 neurons. During OGD the fluo-3/fura red ratio reflecting [Ca2+]i increased rapidly and irreversibly. [Ca2+]i increased to the same degree in Ca2+ depleted medium, and also when both the ryanodine receptors (RyR) and the inositol 1,4,5-trisphosphate (IP3) receptors were blocked. When the endoplasmic reticulum (ER) Ca2+ stores were emptied with thapsigargin no increase in [Ca2+]i was observed independent of extracellular Ca2+. The OGD induced Ca2+ deregulation in isolated CA1 neurons is not prevented by removing Ca2+, or by blocking the IP3– or RyR receptors. However, when SERCA was blocked, no increase in [Ca2+]i was observed suggesting that SERCA dysfunction represents an important mechanism for ischemic Ca2+ overload.  相似文献   

17.
Exposing bovine chromaffin cells to a single 5 ns, high-voltage (5 MV/m) electric pulse stimulates Ca2+ entry into the cells via L-type voltage-gated Ca2+ channels (VGCC), resulting in the release of catecholamine. In this study, fluorescence imaging was used to monitor nanosecond pulse-induced effects on intracellular Ca2+ level ([Ca2+]i) to investigate the contribution of other types of VGCCs expressed in these cells in mediating Ca2+ entry. ω-Conotoxin GVIA and ω-agatoxin IVA, antagonists of N-type and P/Q-type VGCCs, respectively, reduced the magnitude of the rise in [Ca2+]i elicited by a 5 ns pulse. ω-conotoxin MVIIC, which blocks N- and P/Q-type VGCCs, had a similar effect. Blocking L-, N-, and P\Q-type channels simultaneously with a cocktail of VGCC inhibitors abolished the pulse-induced [Ca2+]i response of the cells, suggesting Ca2+ influx occurs only via VGCCs. Lowering extracellular K+ concentration from 5 to 2 mM or pulsing cells in Na+-free medium suppressed the pulse-induced rise in [Ca2+]i in the majority of cells. Thus, both membrane potential and Na+ entry appear to play a role in the mechanism by which nanoelectropulses evoke Ca2+ influx. However, activation of voltage-gated Na+ channels (VGSC) is not involved since tetrodotoxin (TTX) failed to block the pulse-induced rise in [Ca2+]i. These findings demonstrate that a single electric pulse of only 5 ns duration serves as a novel stimulus to open multiple types of VGCCs in chromaffin cells in a manner involving Na+ transport across the plasma membrane. Whether Na+ transport occurs via non-selective cation channels and/or through lipid nanopores remains to be determined.  相似文献   

18.
Powered by the mitochondrial membrane potential, Ca2+ permeates the mitochondria via a Ca2+ channel termed Ca2+ uniporter and is pumped out by a Na+/Ca2+ exchanger, both of which are located on the inner mitochondrial membrane. Mitochondrial Ca2+ transients are critical for metabolic activity and regulating global Ca2+ responses. On the other hand, failure to control mitochondrial Ca2+ is a hallmark of ischemic and neurodegenerative diseases. Despite their importance, identifying the uniporter and exchanger remains elusive and their inhibitors are non-specific. This review will focus on the mitochondrial exchanger, initially describing how it was molecularly identified and linked to a novel member of the Na+/Ca2+ exchanger superfamily termed NCLX. Molecular control of NCLX expression provides a selective tool to determine its physiological role in a variety of cell types. In lymphocytes, NCLX is essential for refilling the endoplasmic reticulum Ca2+ stores required for antigendependent signaling. Communication of NCLX with the store-operated channel in astroglia controls Ca2+ influx and thereby neuro-transmitter release and cell proliferation. The refilling of the Ca2+ stores in the sarcoplasmic reticulum, which is controlled by NCLX, determines the frequency of action potential and Ca2+ transients in cardiomyocytes. NCLX is emerging as a hub for integrating glucose-dependent Na+ and Ca2+ signaling in pancreatic β cells, and the specific molecular control of NCLX expression resolved the controversy regarding its role in neurons and β cells. Future studies on an NCLX knockdown mouse model and identification of human NCLX mutations are expected to determine the role of mitochondrial Ca2+ efflux in organ activity and whether NCLX inactivation is linked to ischemic and/or neurodegenerative syndromes. Structure-function analysis and protein analysis will identify the NCLX mode of regulation and its partners in the inner membrane of the mitochondria.  相似文献   

19.
20.
The characteristics and properties of the increase in cytosolic [Ca2+] that occurs in bovine adrenal medullary chromaffin cells on exposure to angiotensin II have been investigated. In fura-2 loaded cells exposure to a maximally effective concentration of angiotensin II (100 nM) caused a rapid, but transient increase in cytosolic [Ca2+] followed by a lower plateau that was sustained as long as external Ca2+ was present. In the absence of external Ca2+ only the initial brief transient was observed. In cells previously treated with thapsigargin in Ca2+-free medium to deplete the internal Ca2+ stores, angiotensin II caused no increase in cytosolic [Ca2+] when external Ca2+ was absent. Reintroduction of external Ca2+ to thapsigargin-treated, store-depleted cells caused a sustained increase in cytosolic [Ca2+] that was not further increased upon exposure to angiotensin II. Analysis of the data suggests that in bovine chromaffin cells angiotensin II causes Ca2+ entry via a pathway(s) activated as a consequence of internal store mobilization, and entry through this pathway(s) forms the majority of the sustained Ca2+ influx evoked by angiotensin II.  相似文献   

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