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1.
Micromolar Ca2+ from sparks activates Ca2+-sensitive K+ channels in rat cerebral artery smooth muscle 总被引:3,自引:0,他引:3
Perez Guillermo J.; Bonev Adrian D.; Nelson Mark T. 《American journal of physiology. Cell physiology》2001,281(6):C1769
The goal of the present study was to testthe hypothesis that local Ca2+ release events(Ca2+ sparks) deliver high local Ca2+concentration to activate nearby Ca2+-sensitiveK+ (BK) channels in the cell membrane of arterial smoothmuscle cells. Ca2+ sparks and BK channels were examined inisolated myocytes from rat cerebral arteries with laser scanningconfocal microscopy and patch-clamp techniques. BK channels had anapparent dissociation constant for Ca2+ of 19 µM and aHill coefficient of 2.9 at 40 mV. At near-physiological intracellularCa2+ concentration ([Ca2+]i; 100 nM) and membrane potential (40 mV), the open probability of a singleBK channel was low (1.2 × 106). A Ca2+spark increased BK channel activity to 18. Assuming that 1-100% of the BK channels are activated by a single Ca2+ spark, BKchannel activity increases 6 × 105-fold to 6 × 103-fold, which corresponds to ~30 µM to 4 µM sparkCa2+ concentration.1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acidacetoxymethyl ester caused the disappearance of all Ca2+sparks while leaving the transient BK currents unchanged. Our resultssupport the idea that Ca2+ spark sites are in closeproximity to the BK channels and that local[Ca2+]i reaches micromolar levels to activateBK channels. 相似文献
2.
Smani Tarik; Patel Tina; Bolotina Victoria M. 《American journal of physiology. Cell physiology》2008,294(6):C1499
The role of PKC in the regulation of store-operated Ca2+ entry (SOCE) is rather controversial. Here, we used Ca2+-imaging, biochemical, pharmacological, and molecular techniques to test if Ca2+-independent PLA2β (iPLA2β), one of the transducers of the signal from depleted stores to plasma membrane channels, may be a target for the complex regulation of SOCE by PKC and diacylglycerol (DAG) in rabbit aortic smooth muscle cells (SMCs). We found that the inhibition of PKC with chelerythrine resulted in significant inhibition of thapsigargin (TG)-induced SOCE in proliferating SMCs. Activation of PKC by the diacylglycerol analog 1-oleoyl-2-acetyl-sn-glycerol (OAG) caused a significant depletion of intracellular Ca2+ stores and triggered Ca2+ influx that was similar to TG-induced SOCE. OAG and TG both produced a PKC-dependent activation of iPLA2β and Ca2+ entry that were absent in SMCs in which iPLA2β was inhibited by a specific chiral enantiomer of bromoenol lactone (S-BEL). Moreover, we found that PKC regulates TG- and OAG-induced Ca2+ entry only in proliferating SMCs, which correlates with the expression of the specific PKC- isoform. Molecular downregulation of PKC- impaired TG- and OAG-induced Ca2+ influx in proliferating SMCs but had no effect in confluent SMCs. Our results demonstrate that DAG (or OAG) can affect SOCE via multiple mechanisms, which may involve the depletion of Ca2+ stores as well as direct PKC--dependent activation of iPLA2β, resulting in a complex regulation of SOCE in proliferating and confluent SMCs. protein kinase C-; Ca2+-independent phospholipase A2; diacylglycerol; smooth muscle cells 相似文献
3.
Denson Donald D.; Worrell Roger T.; Middleton Pamela; Eaton Douglas C. 《American journal of physiology. Cell physiology》1999,276(1):C201
To test thehypothesis that intracellular Ca2+activation of large-conductanceCa2+-activatedK+ (BK) channels involves thecytosolic form of phospholipase A2 (cPLA2), we first inhibited theexpression of cPLA2 by treating GH3 cells with antisenseoligonucleotides directed at the two possible translation start siteson cPLA2. Western blot analysis and a biochemical assay of cPLA2activity showed marked inhibition of the expression ofcPLA2 in antisense-treated cells.We then examined the effects of intracellularCa2+ concentration([Ca2+]i)on single BK channels from these cells. Open channel probability (Po) for thecells exposed to cPLA2 antisenseoligonucleotides in 0.1 µM intracellularCa2+ was significantly lower thanin untreated or sense oligonucleotide-treated cells, but the voltagesensitivity did not change (measured as the slope of thePo-voltagerelationship). In fact, a 1,000-fold increase in[Ca2+]ifrom 0.1 to 100 µM did not significantly increasePoin these cells, whereas BK channels from cells in the other treatmentgroups showed a normalPo-[Ca2+]iresponse. Finally, we examined the effect of exogenous arachidonic acidon thePoof BK channels from antisense-treated cells. Although arachidonic aciddid significantly increasePo,it did so without restoring the[Ca2+]isensitivity observed in untreated cells. We conclude that although [Ca2+]idoes impart some basal activity to BK channels inGH3 cells, the steepPo-[Ca2+]irelationship that is characteristic of these channels involves cPLA2. 相似文献
4.
The contribution of small-conductance (SKCa) and intermediate-conductance Ca2+-activated K+ (IKCa) channels to the generation of nitric oxide (NO) by Ca2+-mobilizing stimuli was investigated in human umbilical vein endothelial cells (HUVECs) by combining single-cell microfluorimetry with perforated patch-clamp recordings to monitor agonist-evoked NO synthesis, cytosolic Ca2+ transients, and membrane hyperpolarization in real time. ATP or histamine evoked reproducible elevations in NO synthesis and cytosolic Ca2+, as judged by 4-amino-5-methylamino-2',7'-difluorofluorescein (DAF-FM) and fluo-3 fluorescence, respectively, that were tightly associated with membrane hyperpolarizations. Whereas evoked NO synthesis was unaffected by either tetraethylammonium (10 mmol/l) or BaCl2 (50 µmol/l) + ouabain (100 µmol/l), depleting intracellular Ca2+ stores by thapsigargin or removing external Ca2+ inhibited NO production, as did exposure to high (80 mmol/l) external KCl. Importantly, apamin and charybdotoxin (ChTx)/ triarylmethane (TRAM)-34, selective blockers SKCa and IKCa channels, respectively, abolished both stimulated NO synthesis and membrane hyperpolarization and decreased evoked Ca2+ transients. Apamin and TRAM-34 also inhibited an agonist-induced outwardly rectifying current characteristic of SKCa and IKCa channels. Under voltage-clamp control, we further observed that the magnitude of agonist-induced NO production varied directly with the degree of membrane hyperpolarization. Mechanistically, our data indicate that SKCa and IKCa channel-mediated hyperpolarization represents a critical early event in agonist-evoked NO production by regulating the influx of Ca2+ responsible for endothelial NO synthase activation. Moreover, it appears that the primary role of agonist-induced release of intracellular Ca2+ stores is to trigger the opening of both KCa channels along with Ca2+ entry channels at the plasma membrane. Finally, the observed inhibition of stimulated NO synthesis by apamin and ChTx/TRAM-34 demonstrates that SKCa and IKCa channels are essential for NO-mediated vasorelaxation. calcium; endothelium; hyperpolarization; small-conductance calcium-activated potassium channel; intermediate-conductance calcium-activated potassium channel channel 相似文献
5.
Su Z Barker DS Csutora P Chang T Shoemaker RL Marchase RB Blalock JE 《American journal of physiology. Cell physiology》2003,284(2):C497-C505
Thecoupling mechanism between depletion of Ca2+ stores in theendoplasmic reticulum and plasma membrane store-operated ion channelsis fundamental to Ca2+ signaling in many cell types and hasyet to be completely elucidated. Using Ca2+release-activated Ca2+ (CRAC) channels in RBL-2H3 cells asa model system, we have shown that CRAC channels are maintained in theclosed state by an inhibitory factor rather than being opened by theinositol 1,4,5-trisphosphate receptor. This inhibitory role can befulfilled by the Drosophila protein INAD (inactivation-noafter potential D). The action of INAD requires Ca2+ andcan be reversed by a diffusible Ca2+ influx factor. Thusthe coupling between the depletion of Ca2+ stores and theactivation of CRAC channels may involve a mammalian homologue of INADand a low-molecular-weight, diffusible store-depletion signal. 相似文献
6.
Khan Raheela N.; Smith Stephen K.; Morrison J. J.; Ashford Michael L.J. 《American journal of physiology. Cell physiology》1997,273(5):C1721
Two populations,Ca2+-dependent(BKCa) andCa2+-independentK+ (BK) channels of largeconductance were identified in inside-out patches of nonlabor and laborfreshly dispersed human pregnant myometrial cells, respectively.Cell-attached recordings from nonlabor myometrial cells frequentlydisplayed BKCa channel openings characterized by a relatively low open-state probability, whereas similar recordings from labor tissue displayed either no channel openings or consistently high levels of channel activity that oftenexhibited clear, oscillatory activity. In inside-out patch recordings,Ba2+ (2-10 mM),4-aminopyridine (0.1-1 mM), andShaker B inactivating peptide("ball peptide") blocked theBKCa channel but were much lesseffective on BK channels. Application of tetraethylammonium toinside-out membrane patches reduced unitary current amplitude ofBKCa and BK channels, withdissociation constants of 46 mM and 53 µM, respectively.Tetraethylammonium applied to outside-out patches decreased the unitaryconductance of BKCa and BKchannels, with dissociation constants of 423 and 395 µM,respectively. These results demonstrate that the properties of humanmyometrial large-conductance K+channels in myocytes isolated from laboring patients are significantly different from those isolated from nonlaboring patients. 相似文献
7.
Activators of protein kinase C decrease Ca2+ spark frequency in smooth muscle cells from cerebral arteries 总被引:3,自引:0,他引:3
Bonev Adrian D.; Jaggar Jonathan H.; Rubart Michael; Nelson Mark T. 《American journal of physiology. Cell physiology》1997,273(6):C2090
LocalCa2+ transients("Ca2+ sparks") caused bythe opening of one or the coordinated opening of a number of tightlyclustered ryanodine-sensitiveCa2+-release (RyR) channels in thesarcoplasmic reticulum (SR) activate nearbyCa2+-dependentK+(KCa) channels to cause anoutward current [referred to as a "spontaneous transientoutward current" (STOC)]. TheseKCa currents cause membranepotential hyperpolarization of arterial myocytes, which would lead tovasodilation through decreasingCa2+ entry throughvoltage-dependent Ca2+ channels.Therefore, modulation of Ca2+spark frequency should be a means to regulation ofKCa channel currents and hencemembrane potential. We examined the frequency modulation ofCa2+ sparks and STOCs byactivation of protein kinase C (PKC). The PKC activators, phorbol12-myristate 13-acetate (PMA; 10 nM) and 1,2-dioctanoyl-sn-glycerol (1 µM),decreased Ca2+ spark frequency by72% and 60%, respectively, and PMA reduced STOC frequency by 83%.PMA also decreased STOC amplitude by 22%, which could be explained byan observed reduction (29%) inKCa channel open probability inthe absence of Ca2+ sparks. Thereduction in STOC frequency occurred in the presence of an inorganicblocker (Cd2+) ofvoltage-dependent Ca2+ channels.The reduction in Ca2+ sparkfrequency did not result from SRCa2+ depletion, sincecaffeine-induced Ca2+ transientsdid not decrease in the presence of PMA. These results suggest thatactivators of PKC can modulate the frequency ofCa2+ sparks, through an effect onthe RyR channel, which would decrease STOC frequency (i.e.,KCa channel activity). 相似文献
8.
Beskina O Miller A Mazzocco-Spezzia A Pulina MV Golovina VA 《American journal of physiology. Cell physiology》2007,293(3):C1103-C1111
Many neurodegenerative disorders are accompanied by chronic glial activation, which is characterized by the abundant production of proinflammatory cytokines, such as IL-1. IL-1 disrupts Ca2+ homeostasis and stimulates astrocyte reactivity. The mechanisms by which IL-1 induces Ca2+ dysregulation are not completely defined. Here, we examined how acute and chronic (24–48 h) treatment with IL-1 affect Ca2+ homeostasis in freshly dissociated and primary cultured mouse cortical astrocytes. Cytosolic free Ca2+ concentration ([Ca2+]cyt) was measured with fura-2 using digital imaging. An acute application of 10 ng/ml IL-1 induced Ca2+ mobilization from intracellular stores and activated store-operated Ca2+ entry (SOCE) and receptor-operated Ca2+ entry (ROCE) in both freshly dissociated and cultured actrocytes. Treatment of cultured astrocytes with IL-1 for 24 and 48 h elevated resting [Ca2+]cyt, decreased Ca2+ store content [associated with sarco(endo)plasmic reticulum Ca2+-ATPase 2b downregulation], and augmented ROCE. Based on evidence that receptor-operated, but not store-operated Ca2+ channels are Ba2+ permeable, Ba2+ entry was used to distinguish receptor-operated Ca2+ channels from store-operated Ca2+ channels. ROCE was activated by the diacylglycerol analog, 1-oleoyl-2-acetyl-sn-glycerol (OAG). In the presence of extracellular Ba2+, OAG-induced elevations of cytosolic Ba2+ (fura-2 340-to-380-nm ratio) were significantly larger in astrocytes treated with IL-1. These changes in IL-1-treated astrocytes correlate with augmented expression of transient receptor potential cation channel (TRPC)6 protein, which likely mediates ROCE. Knockdown of the TRPC6 gene markedly reduced ROCE. The data suggest that IL-1-induced dysregulation of Ca2+ homeostasis is the result of enhanced ROCE and TRPC6 expression. The disruption of Ca2+ homeostasis appears to be an upstream component in the cascade of IL-1-activated pathways leading to neurodegeneration. transient receptor potential cation channel proteins 相似文献
9.
Store-operated Ca2+ entry modulates sarcoplasmic reticulum Ca2+ loading in neonatal rabbit cardiac ventricular myocytes 总被引:1,自引:0,他引:1
Huang J van Breemen C Kuo KH Hove-Madsen L Tibbits GF 《American journal of physiology. Cell physiology》2006,290(6):C1572-C1582
Store-operated Ca2+ entry (SOCE), which is Ca2+ entry triggered by the depletion of intracellular Ca2+ stores, has been observed in many cell types, but only recently has it been suggested to occur in cardiomyocytes. In the present study, we have demonstrated SOCE-dependent sarcoplasmic reticulum (SR) Ca2+ loading (loadSR) that was not altered by inhibition of L-type Ca2+ channels, reverse mode Na+/Ca2+ exchange (NCX), or nonselective cation channels. In contrast, lowering the extracellular [Ca2+] to 0 mM or adding either 0.5 mM Zn2+ or the putative store-operated channel (SOC) inhibitor SKF-96365 (100 µM) inhibited loadSR at rest. Interestingly, inhibition of forward mode NCX with 30 µM KB-R7943 stimulated SOCE significantly and resulted in enhanced loadSR. In addition, manipulation of the extracellular and intracellular Na+ concentrations further demonstrated the modulatory role of NCX in SOCE-mediated SR Ca2+ loading. Although there is little knowledge of SOCE in cardiomyocytes, the present results suggest that this mechanism, together with NCX, may play an important role in SR Ca2+ homeostasis. The data reported herein also imply the presence of microdomains unique to the neonatal cardiomyocyte. These findings may be of particular importance during open heart surgery in neonates, in which uncontrolled SOCE could lead to SR Ca2+ overload and arrhythmogenesis. cardiac ontogeny; cardiac excitation-contraction coupling; calcium homeostasis 相似文献
10.
Phototropins (phot1 and phot2) are blue light (BL) receptorsthat mediate responses including phototropism, chloroplast movementand stomatal opening, and increased cytosolic Ca2+. BL absorbedby phototropins activates plasma membrane H+-ATPase in guardcells, resulting in membrane hyperpolarization, and drives K+uptake and stomatal opening. However, it is unclear whetherthe phototropin-mediated Ca2+ increase activates the H+-ATPase.Here, we determined cytosolic Ca2+ concentrations in guard cellprotoplasts (GCPs) from Arabidopsis transformed with aequorin.Cytosolic Ca2+ increased rapidly in response to BL in GCPs fromboth the wild type and phot1 phot2 double mutants, but was mostlysuppressed by an inhibitor of photosynthetic electron flow (DCMU).With depleted external K+, we observed another slower Ca2+ increase,which was phototropin- dependent. Fusicoccin, a H+-ATPase activator,mimicked the effect of BL. The slow Ca2+ increase thus appearsto result from membrane hyperpolarization. The slow Ca2+ increasewas suppressed by external K+ and was restored by blockers ofinward-rectifying K+ channels, CsCl and tetraethylammonium,suggesting the preferential uptake of K+ over Ca2+. Such efficientK+ uptake in response to BL was not found in mesophyll cells.Both the fast and the slow Ca2+ increases were inhibited byCa2+ channel blockers (CoCl2 and LaCl3) and a chelating agent(EGTA). These results indicate that the phototropin-mediatedCa2+ increase was not observed prior to H+-ATPase activationin guard cells and that Ca2+ entered guard cells via Ca2+ channelsthrough photosynthesis and phototropin-mediated membrane hyperpolarization. 相似文献
11.
Stimulation of -adrenoceptors contributes to the relaxation of urinary bladder smooth muscle (UBSM) through activation of large-conductance Ca2+-activated K+ (BK) channels. We examined the mechanisms by which -adrenoceptor stimulation leads to an elevation of the activity of BK channels in UBSM. Depolarization from 70 to +10 mV evokes an inward L-type dihydropyridine-sensitive voltage-dependent Ca2+ channel (VDCC) current, followed by outward steady-state and transient BK current. In the presence of ryanodine, which blocks the transient BK currents, isoproterenol, a nonselective -adrenoceptor agonist, increased the VDCC current by 25% and the steady-state BK current by 30%. In the presence of the BK channel inhibitor iberiotoxin, isoproterenol did not cause activation of the remaining steady-state K+ current component. Decreasing Ca2+ influx through VDCC by nifedipine or depolarization to +80 mV suppressed the isoproterenol-induced activation of the steady-state BK current. Unlike forskolin, isoproterenol did not change significantly the open probability of single BK channels in the absence of Ca2+ sparks and with VDCC inhibited by nifedipine. Isoproterenol elevated Ca2+ spark (local intracellular Ca2+ release through ryanodine receptors of the sarcoplasmic reticulum) frequency and associated transient BK currents by 1.4-fold. The data support the concept that in UBSM -adrenoceptor stimulation activates BK channels by elevating Ca2+ influx through VDCC and by increasing Ca2+ sparks, but not through a Ca2+-independent mechanism. This study reveals key regulatory molecular and cellular mechanisms of -adrenergic regulation of BK channels in UBSM that could provide new targets for drugs in the treatment of bladder dysfunction. Ca2+ sparks; voltage-dependent Ca2+ channel; ryanodine receptor 相似文献
12.
Modulation of intracellular Ca2+ release and capacitative Ca2+ entry by CaMKII inhibitors in bovine vascular endothelial cells 总被引:2,自引:0,他引:2
The effects of inhibitors of CaMKII on intracellular Ca2+ signaling were examined in single calf pulmonary artery endothelial (CPAE) cells using indo-1 microfluorometry to measure cytoplasmic Ca2+ concentration ([Ca2+]i). The three CaMKII inhibitors, KN-93, KN-62, and autocamtide-2-related inhibitory peptide (AIP), all reduced the plateau phase of the [Ca2+]i transient evoked by stimulation with extracellular ATP. Exposure to KN-93 or AIP alone in the presence of 2 mM extracellular Ca2+ resulted in a dose-dependent increase of [Ca2+]i consisting of a rapid and transient Ca2+ spike followed by a small sustained plateau phase of elevated [Ca2+]i. Exposure to KN-93 in the absence of extracellular Ca2+ caused a transient rise of [Ca2+]i, suggesting that exposure to CaMKII inhibitors directly triggered release of Ca2+ from intracellular endoplasmic reticulum (ER) Ca2+ stores. Repetitive stimulation with KN-93 and ATP, respectively, revealed that both components released Ca2+ largely from the same store. Pretreatment of CPAE cells with the membrane-permeable inositol 1,4,5-trisphosphate (IP3) receptor blocker 2-aminoethoxydiphenyl borate caused a significant inhibition of the KN-93-induced Ca2+ response, suggesting that exposure to KN-93 affects Ca2+ release from an IP3-sensitive store. Depletion of Ca2+ stores by exposure to ATP or to the ER Ca2+ pump inhibitor thapsigargin triggered robust capacitative Ca2+ entry (CCE) signals in CPAE cells that could be blocked effectively with KN-93. The data suggest that in CPAE cells, CaMKII modulates Ca2+ handling at different levels. The use of CaMKII inhibitors revealed that in CPAE cells, the most profound effects of CaMKII are inhibition of release of Ca2+ from intracellular stores and activation of CCE. Ca2+/calmodulin-dependent kinase II; calcium regulation; capacitative calcium entry 相似文献
13.
Lee S Kim JC Li Y Son MJ Woo SH 《American journal of physiology. Cell physiology》2008,294(4):C966-C976
This study examines whether fluid pressure (FP) modulates the L-type Ca2+ channel in cardiomyocytes and investigates the underlying cellular mechanism(s) involved. A flow of pressurized (16 dyn/cm2) fluid, identical to that bathing the myocytes, was applied onto single rat ventricular myocytes using a microperfusion method. The Ca2+ current (ICa) and cytosolic Ca2+ signals were measured using a whole cell patch-clamp and confocal imaging, respectively. It was found that the FP reversibly suppressed ICa (by 25%) without altering the current-voltage relationships, and it accelerated the inactivation of ICa. The level of ICa suppression by FP depended on the level and duration of pressure. The Ba2+ current through the Ca2+ channel was only slightly decreased by the FP (5%), suggesting an indirect inhibition of the Ca2+ channel during FP stimulation. The cytosolic Ca2+ transients and the basal Ca2+ in field-stimulated ventricular myocytes were significantly increased by the FP. The effects of the FP on the ICa and on the Ca2+ transient were resistant to the stretch-activated channel inhibitors, GsMTx-4 and streptomycin. Dialysis of myocytes with high concentrations of BAPTA, the Ca2+ buffer, eliminated the FP-induced acceleration of ICa inactivation and reduced the inhibitory effect of the FP on ICa by 80%. Ryanodine and thapsigargin, abolishing sarcoplasmic reticulum Ca2+ release, eliminated the accelerating effect of FP on the ICa inactivation, and they reduced the inhibitory effect of FP on the ICa. These results suggest that the fluid pressure indirectly suppresses the Ca2+ channel by enhancing the Ca2+-induced intracellular Ca2+ release in rat ventricular myocytes. L-type Ca2+ current; fluid pressure; ventricular myocytes; cytosolic Ca2+ transient 相似文献
14.
Coupling strength between localized Ca(2+) transients and K(+) channels is regulated by protein kinase C 总被引:1,自引:0,他引:1
Bayguinov O Hagen B Kenyon JL Sanders KM 《American journal of physiology. Cell physiology》2001,281(5):C1512-C1523
Localized Ca2+ transients resulting from inositoltrisphosphate (IP3)-dependent Ca2+ releasecouple to spontaneous transient outward currents (STOCs) in murinecolonic myocytes. Confocal microscopy and whole cell patch-clamptechniques were used to investigate coupling between localizedCa2+ transients and STOCs. Colonic myocytes were loadedwith fluo 3. Reduction in external Ca2+([Ca2+]o) reduced localized Ca2+transients but increased STOC amplitude and frequency. Simultaneous recordings of Ca2+ transients and STOCs showed increasedcoupling strength between Ca2+ transients and STOCs when[Ca2+]o was reduced. Gd3+ (10 µM) did not affect Ca2+ transients but increased STOCamplitude and frequency. Similarly, an inhibitor of Ca2+influx,1-2-(4-methoxyphenyl)-2-[3-(4-methoxyphenyl)propoxy]ethyl-1H-imidazole (SKF-96365), increased STOC amplitude and frequency. A protein kinase C(PKC) inhibitor, GF-109203X, also increased the amplitude and frequencyof STOCs but had no effect on Ca2+ transients. Phorbol12-myristate 13-acetate (1 µM) reduced STOC amplitude and frequencybut did not affect Ca2+ transients. 4-Phorbol (1 µM)had no effect on STOCs or Ca2+ transients. Single channelstudies indicated that large-conductance Ca2+-activatedK+ (BK) channels were inhibited by aCa2+-dependent PKC. In summary 1)Ca2+ release from IP3 receptor-operated storesactivates Ca2+-activated K+ channels;2) Ca2+ influx through nonselective cationchannels facilitates activation of PKC; and 3) PKC reducesthe Ca2+ sensitivity of BK channels, reducing the couplingstrength between localized Ca2+ transients and BK channels. 相似文献
15.
VCAM-1-induced inwardly rectifying K(+) current enhances Ca(2+) entry in human THP-1 monocytes 总被引:1,自引:0,他引:1
Hyperpolarization in human leukemia THP-1 monocytes adherent tovascular cell adhesion molecule (VCAM)-1 is due to an induction ofinwardly rectifying K+ currents(Iir) (Colden-Stanfield M and Gallin EK,Am J Physiol Cell Physiol 275: C267-C277, 1998).We determined whether the VCAM-1-induced hyperpolarization issufficient to augment the increase in intracellular free calcium([Ca2+]i) produced by Ca2+ storedepletion with thapsigargin (TG) and readdition of external CaCl2 in fura 2-loaded THP-1 monocytes. Whereas there was a2.1-fold increase in [Ca2+]i in monocytesbound to glass for 5 h in response to TG and CaCl2 addition, adherence to VCAM-1 produced a 5-fold increase in[Ca2+]i. Depolarization of monocytes adherentto VCAM-1 by Iir blockade or exposure to high[K+] abolished the enhancement of the peak[Ca2+]i response. In monocytes bound toglass, hyperpolarization of the membrane potential with valinomycin, aK+ ionophore, to the level of hyperpolarization seen incells adherent to VCAM-1 produced similar changes in peak[Ca2+]i. Adherence of monocytes to E-selectinproduced a similar peak [Ca2+]i to cellsbound to glass. Thus monocyte adherence to the physiological substrateVCAM-1 produces a hyperpolarization that is sufficient to enhanceCa2+ entry and may impact Ca2+-dependentmonocyte function. 相似文献
16.
Significance of Ca2+ and K+ for the complex morphogenesis ofMicrasterias, which takes place through multipolar tip growth,was investigated. Studies with different external Ca2+ concentrationsand Ca2+ channel inhibitors LaCl3 and verapamil indicate thatCa2+ and Ca2+ channels are essential in the development, whiletreatments with different K+ concentrations and K+ channel inhibitorTEA demonstrate that potassium or K+ channels are not neededin the process, albeit the existence of K+ channels. K+ is notneeded even for the regulation of turgor pressure, which wasfound to decrease clearly during cell development. The plasmamembrane ATPase inhibitors diethylstilbesterol (DES) and Na-orthovanadatestop morphogenesis and indicate the importance of ion pumpsin the developmental process. Both supraoptimal, external K+and Ca2+ cause abundant Ca2+ precipitate formation in chloroplasts,which shows that chloroplasts are important in regulation ofcytoplasmic Ca2+ metabolism and that K+ activates the uptakeof Ca2+ through Ca2+ channels. (Received June 13, 1995; Accepted September 13, 1996) 相似文献
17.
Copello JA Zima AV Diaz-Sylvester PL Fill M Blatter LA 《American journal of physiology. Cell physiology》2007,292(6):C2129-C2140
During the cardiac action potential, Ca2+ entry through dyhidropyridine receptor L-type Ca2+ channels (DHPRs) activates ryanodine receptors (RyRs) Ca2+-release channels, resulting in massive Ca2+ mobilization from the sarcoplasmic reticulum (SR). This global Ca2+ release arises from spatiotemporal summation of many localized elementary Ca2+-release events, Ca2+ sparks. We tested whether DHPRs modulate Ca2+sparks in a Ca2+ entry-independent manner. Negative modulation by DHPR of RyRs via physical interactions is accepted in resting skeletal muscle but remains controversial in the heart. Ca2+ sparks were studied in cat cardiac myocytes permeabilized with saponin or internally perfused via a patch pipette. Bathing and pipette solutions contained low Ca2+ (100 nM). Under these conditions, Ca2+ sparks were detected with a stable frequency of 3–5 sparks·s–1·100 µm–1. The DHPR blockers nifedipine, nimodipine, FS-2, and calciseptine decreased spark frequency, whereas the DHPR agonists Bay-K8644 and FPL-64176 increased it. None of these agents altered the spatiotemporal characteristics of Ca2+ sparks. The DHPR modulators were also without effect on SR Ca2+ load (caffeine-induced Ca2+ transients) or sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) activity (Ca2+ loading rates of isolated SR microsomes) and did not change cardiac RyR channel gating (planar lipid bilayer experiments). In summary, DHPR modulators affected spark frequency in the absence of DHPR-mediated Ca2+ entry. This action could not be attributed to a direct action of DHPR modulators on SERCA or RyRs. Our results suggest that the activity of RyR Ca2+-release units in ventricular myocytes is modulated by Ca2+ entry-independent conformational changes in neighboring DHPRs. exitation-contraction coupling; ryanodine receptor; sarco(endo)plasmic reticulum Ca2+-ATPase; dihydropyridine receptor; sarcoplasmic reticulum 相似文献
18.
《Cell calcium》2020
Neuroendocrine adrenal chromaffin cells release neurohormones catecholamines in response to Ca2+ entry via voltage-gated Ca2+ channels (VGCCs). Adrenal chromaffin cells also express non-voltage-gated channels, which may conduct Ca2+ at negative membrane potentials, whose role in regulation of exocytosis is poorly understood. We explored how modulation of Ca2+ influx at negative membrane potentials affects basal cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis in metabolically intact voltage-clamped bovine adrenal chromaffin cells. We found that in these cells, Ca2+ entry at negative membrane potentials is balanced by Ca2+ extrusion by the Na+/Ca2+ exchanger and that this balance can be altered by membrane hyperpolarization or stimulation with an inflammatory hormone bradykinin. Membrane hyperpolarization or application of bradykinin augmented Ca2+-carrying current at negative membrane potentials, elevated basal [Ca2+]i, and facilitated synchronous exocytosis evoked by the small amounts of Ca2+ injected into the cell via VGCCs (up to 20 pC). Exocytotic responses evoked by the injections of the larger amounts of Ca2+ via VGCCs (> 20 pC) were suppressed by preceding hyperpolarization. In the absence of Ca2+ entry via VGCCs and Ca2+ extrusion via the Na+/Ca2+ exchanger, membrane hyperpolarization induced a significant elevation in [Ca2+]i and asynchronous exocytosis. Our results indicate that physiological interferences, such as membrane hyperpolarization and/or activation of non-voltage-gated Ca2+ channels, modulate basal [Ca2+]i and, consequently, segregation of exocytotic vesicles and their readiness to be released spontaneously and in response to Ca2+ entry via VGCCs. These mechanisms may play role in homeostatic plasticity of neuronal and endocrine cells. 相似文献
19.
Murata Yoshiyuki; Yoshihashi Manabu; Obi Ichiro; Kakutani Tadaaki 《Plant & cell physiology》1998,39(10):1039-1044
The patch-clamp technique was used to study effect of the Ca2+on K+ channels in the plasma membrane of protoplasts isolatedfrom tobacco (Nicotiana tabacum L., cv. Bright Yellow) culturedcells in suspension. The outward rectifying whole-cell K+ currentswere not affected by in-tracellular Ca2+, but they were reducedwith increasing extracellular Ca2+. Neither extracellular norintracellular Ca2+ affected the permeability ratios (pK+/PNa+)of the plasma membrane. These results suggest that the inhibitionof outward-rectifying K+ channels by extracellular Ca2+may partiallycontribute towards the mitigation of detrimental effects ofsalinity on growth by extracellular Ca2+. (Received January 19, 1998; Accepted July 30, 1998) 相似文献
20.
Seo J. T.; Sugiya H.; Lee S. I.; Steward M. C.; Elliott A. C. 《American journal of physiology. Cell physiology》1999,276(4):C915
We used theCa2+-sensitive fluorescent dyefura 2, together with measurements of intracellularD-myo-inositol1,4,5-trisphosphate [Ins(1,4,5)P3],to assess the inhibitory effects of caffeine on signal transduction viaG protein-coupled receptor pathways in isolated rat mandibular salivaryacinar cells. ACh, norepinephrine (NE), and substance P (SP) all evokedsubstantial increases in the intracellular freeCa2+ concentration([Ca2+]i).Responses to ACh and NE were markedly inhibited by prior application of20 mM caffeine. The inhibitory effect of caffeine was not reproduced byphosphodiesterase inhibition with IBMX or addition of cell-permeantdibutyryl cAMP. In contrast to the ACh and NE responses, the[Ca2+]iresponse to SP was unaffected by caffeine. Despite this, SP and AChappeared to mobilize Ca2+ from acommon intracellular pool. Measurements of agonist-induced changes inIns(1,4,5)P3levels confirmed that caffeine inhibited the stimulus-response couplingpathway at a point beforeIns(1,4,5)P3 generation. Caffeine did not, however, inhibit[Ca2+]iresponses evoked by direct activation of G proteins with 40 mMF. These data show thatcaffeine inhibits G protein-coupled signal transduction in these cellsat some element that is common to the muscarinic and -adrenergicsignaling pathways but is not shared by the SP signaling pathway. Wesuggest that this element might be a specific structural motif on the Gprotein-coupled muscarinic and -adrenergic receptors. 相似文献