Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.6.1.3 (ATPase)
65,361 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Calcium-dependent regulatory mechanisms participate in diverse developmentally, hormonally, and environmentally regulated processes, with the precise control of cytosolic Ca2+ concentration being critical to such mechanisms. In plant cells, P-type Ca(2+)-ATPases localized in the plasma membrane and the endoplasmic reticulum are thought to play a central role in regulating cytoplasmic Ca2+ concentrations. Ca(2+)-ATPase activity has been identified in isolated plant cell membranes, but the protein has not been characterized at the molecular level. We have isolated a partial-length cDNA (LCA1) and a complete genomic clone (gLCA13) encoding a putative endoplasmic reticulum-localized Ca(2+)-ATPase in tomato. The deduced amino acid sequence specifies a protein (Lycopersicon Ca(2+)-ATPase) of 1048 amino acids with a molecular mass of 116 kDa, eight probable transmembrane domains, and all of the highly conserved functional domains common to P-type cation-translocating ATPases. In addition, the protein shares approximately 50% amino acid sequence identify with animal sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases but less than 30% identity with other P-type ATPases. Genomic DNA blot hybridization analysis indicates that the Lycopersicon Ca(2+)-ATPase is encoded by a single gene. RNA blot hybridization analysis indicates the presence of three transcript sizes in root tissue and a single, much less abundant, transcript in leaves. Lycopersicon Ca(2+)-ATPase mRNA levels increase dramatically upon a 1-day exposure to 50 mM NaCl. Thus this report describes the primary structure of a higher-plant Ca(2+)-ATPase and the regulation of its mRNA abundance by salt stress.
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PMID:Higher plant Ca(2+)-ATPase: primary structure and regulation of mRNA abundance by salt. 138 45

The fast-twitch skeletal muscle Ca(2+)-ATPase isoenzyme, SERCA1a, is localized in chick skeletal myotubes to both the sarcoplasmic reticulum (SR) and to the nuclear envelope, an extension of the endoplasmic reticulum (ER). The ER labeling remained after cycloheximide treatment, indicating that it did not represent newly synthesized SERCA1a in transit to the SR. Expression of the cDNA encoding SERCA1a in cultured non-muscle cells led to the localization of the enzyme in the ER, as indicated by organelle morphology and the co-localization of SERCA1a with the endogenous ER luminal protein, BiP. Immunopurification analysis showed that SERCA1a was not bound to BiP, nor was any degradation apparent. Thus, the SR Ca(2+)-ATPase appears to contain ER targeting information.
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PMID:The sarcoplasmic reticulum Ca(2+)-ATPase, SERCA1a, contains endoplasmic reticulum targeting information. 138 45

The free Ca2+ concentrations in the nucleus ([Ca2+]n) and cytoplasm ([Ca2+]c) of cultured smooth muscle cells were estimated using the fluorescent dye indo-1 and the ACAS 570 confocal laser microscope. In resting DDT1MF2 smooth muscle cells [Ca2+]n was found to be lower than [Ca2+]c. Both values increased transiently in response to histamine (100 microM), but during this stimulation [Ca2+]n exceeded [Ca2+]c. Maximal increase of [Ca2+]n was observed in the center of the nucleus, and a maximal increase of [Ca2+]c was observed in the immediate vicinity of the plasma membrane. A similar response was obtained with other agonists, such as carbachol or ATP. Comparable results with ATP were obtained in cultured aorta cells. The differential rise of [Ca2+]n over [Ca2+]c in DDT1MF2 cells did not occur during either spontaneous release of Ca2+ or Ca2+ release induced by caffeine (7.5 mM). The differential rise during histamine stimulation was abolished by the presence of the intercalating substance ethidium bromide. Thapsigargin, a presumed specific inhibitor of the endoplasmic reticulum Ca(2+)-Mg(2+)-adenosine-triphosphatase, abolished the Ca2+ gradient between nucleus and cytosol at rest. During subsequent histamine stimulation the Ca2+ increase was largely blocked in both compartments and attained similar levels. We propose that the lower value of [Ca2+]n at rest is dependent on an active Ca2+ extrusion system. The differential rise of [Ca2+]n over [Ca2+]c during agonist stimulation can be explained by an influx of Ca2+ from perinuclear stores and/or by a release of intranuclear Ca2+ possibly mediated by a process dependent on the inositol lipid metabolism.
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PMID:Differences in regulation between nuclear and cytoplasmic Ca2+ in cultured smooth muscle cells. 138 89

A transient rise in intracellular Ca2+ during fertilization is necessary for activation of the quiescent sea urchin egg. Several mechanisms contribute to the rise in Ca2+ including influx across the egg plasma membrane and release from intracellular stores. The egg contains both IP3-sensitive and -insensitive Ca2+ release mechanisms and in this study we have used single-cell spectrofluorimetry to examine the effects of caffeine and ryanodine on Ca2+ release in eggs preloaded with fura 2. Caffeine induced a small Ca2+ release that was insensitive to heparin or ruthenium red. Ca2+ liberation by caffeine could be augmented by prior treatment with thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ ATPase. Variable Ca2+ releases were observed in response to microinjection of ryanodine. The action of ryanodine appeared to be enhanced by prior injection of heparin and partially inhibited by ruthenium red. The release of Ca2+ by caffeine or ryanodine was generally insufficient to trigger cortical granule exocytosis, thus these eggs could be fertilized and a second Ca2+ release during fertilization was measured. Unlike the caffeine- and ryanodine-sensitive Ca(2+)-induced Ca2+ release mechanism in somatic cells, the graded responses in eggs suggested this caffeine- and ryanodine-sensitive release mechanism is not sensitive to sudden changes in Ca2+. Thus we could examine the combined actions of caffeine and ryanodine on Ca2+ release, which were synergistic. Caffeine treatment of ryanodine-injected eggs or ryanodine injection of caffeine-treated eggs stimulated a Ca2+ release significantly larger than the release by either drug independently. The experiments presented here suggest that sea urchin eggs liberate Ca2+ in response to caffeine and ryanodine; however, the regulation of this release differs from that described for caffeine- and ryanodine-sensitive Ca(2+)-induced Ca2+ release of somatic cells.
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PMID:Synergistic release of calcium in sea urchin eggs by caffeine and ryanodine. 138 66

At fertilization, the sperm initiates development of the mouse egg by inducing a large transient increase in the intracellular Ca2+ concentration ([Ca2+]i), which is followed by repetitive transient increases in [Ca2+]i. To determine how the repetitive Ca2+ transients are produced, thapsigargin, an inhibitor of the endoplasmic reticulum Ca-ATPase, was used to deplete intracellular Ca2+ stores within the egg. In the unfertilized egg, thapsigargin (1-50 microM) caused a slowly rising and falling transient increase in [Ca2+]i with or without extracellular Ca2+. An influx pathway for Ca2+ is activated by thapsigargin, since an immediate increase in [Ca2+]i occurred when Ca2+ was added to eggs after thapsigargin treatment in a Ca2+, Mg(2+)-free medium. This suggests that Ca2+ entry in the mouse egg may be coupled to the emptying of an intracellular store. The magnitude of the first Ca2+ transient at fertilization was reduced by as much as 84% in eggs pretreated with thapsigargin. Reduction of extracellular Ca2+, by addition of a Ca2+ chelator, suppressed the repetitive Ca2+ transients following fertilization. The Ca2+ transients also require filling of an intracellular store; they were suppressed when thapsigargin was added before or after fertilization. These results support the hypothesis that the first sperm-induced Ca2+ transient at fertilization depletes an intracellular Ca2+ store, triggering an increase in plasma membrane Ca2+ permeability, and that the enhanced Ca2+ influx causes repetitive Ca2+ transients due to the periodic filling and emptying of an intracellular Ca2+ store.
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PMID:Thapsigargin activates a calcium influx pathway in the unfertilized mouse egg and suppresses repetitive calcium transients in the fertilized egg. 138 38

Continuous superfusion of rat glioma cells with medium containing bradykinin (from 0.2 nM) induced a transient hyperpolarization followed by regular hyperpolarizing oscillations of the membrane potential. Similar repetitive hyperpolarizing oscillations were caused by extracellularly applied bradykinin or muscarine or by intracellularly injected GTP-gamma-S. The frequency of the oscillations was 1 per minute at bradykinin concentrations ranging from 0.2 nM to 2 microM, but the amplitude and duration increased with rising peptide concentration. The muscarine-induced oscillations were blocked by atropine. In the presence of extracellular Ca2+, the substances thapsigargin, 2,5-di(tert-butyl)-1,4-benzohydroquinone (tBuBHQ), and ionomycin reversibly suppressed the bradykinin-induced oscillations. Thapsigargin and tBuBHA, which are known to block the Ca2+ ATPase of endoplasmic reticulum, caused a transient rise in cytosolic Ca2+ activity, monitored with Fura-2, in suspensions of rat glioma cells or of mouse neuroblastoma-rat glioma hybrid cells. After a transient Ca2+ rise caused by thapsigargin, tBuBHQ, or ionomycin, the Ca2+ response to bradykinin which is known to be due to release of Ca2+ from internal stores was suppressed. This indicates that thapsigargin and tBuBHQ deplete internal Ca2+ stores as already seen previously for ionomycin. Thus, the inhibition of the membrane potential oscillations by thapsigargin, tBuBHQ, and ionomycin indicates that the oscillations are associated with activation of InsP3-sensitive Ca2+ stores. In some cells composite oscillation patterns which consisted of two independent oscillations with different amplitudes that overlapped additively were seen. We discuss that this pattern and the concentration dependency of the oscillations could be due to "quantal" Ca2+ release from stores with different inositol 1,4,5-triphosphate sensitivities. Subsidence of the oscillations after omission of extracellular Ca2+ seems to be due to a lack of replenishment of the intracellular stores with Ca2+, which comes from the extracellular compartment.
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PMID:Bradykinin and muscarine induce Ca(2+)-dependent oscillations of membrane potential in rat glioma cells indicating a rhythmic Ca2+ release from internal stores: thapsigargin and 2,5-di(tert-butyl)-1, 4-benzohydroquinone deplete InsP3-sensitive Ca2+ stores in glioma and in neuroblastoma-glioma hybrid cells. 139 96

Cytosolic free Ca2+ rises in pancreatic beta-cells in response to glucose stimulation and is part of the coupling to insulin secretion. This study evaluates a possible role for cytosolic long chain acyl-CoA esters in modulating Ca2+ handling by clonal beta-cells (HIT). Intact cells incubated with 20 microM free palmitic acid exhibited a 40% decrease in basal cytosolic free Ca2+. In contrast, acyl-CoA esters, up to a chain length of 16, but not the corresponding fatty acids, significantly lowered the Ca2+ set point maintained by cells permeabilized with saponin. The maximum response to the various acyl-CoA esters increased with increasing chain length, with no differences in the half-maximally effective concentration of 0.5 microM. Long chain acyl-CoA esters caused a 40-50% increase in 45Ca2+ influx into a non-mitochondrial pool in the permeabilized HIT cells, consistent with a stimulatory effect on the endoplasmic reticulum Ca(2+)-ATPase activity, but did not affect inositol 1,4,5-trisphosphate-induced Ca(2+)-efflux. Thapsigargin, an inhibitor of endoplasmic reticulum Ca(2+)-ATPase activity, blocked the decrease in the Ca2+ set point caused by acyl-CoA esters. The ability of acyl-CoA esters to lower the Ca2+ set point depended on the ATP/ADP ratio (or free ADP); the Ca2+ set point was lowered by 36 +/- 3.6% at an ATP/ADP ratio of 90 and by 14 +/- 1.9% at an ATP/ADP ratio of 7. Depletion of cellular protein kinase C did not prevent the acyl-CoA-induced lowering of the Ca2+ set point. These findings suggest that the increases in long chain acyl-CoA esters may play a role in restoring cytosolic free Ca2+ through activation of Ca(2+)-ATPases.
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PMID:Acyl-CoA esters modulate intracellular Ca2+ handling by permeabilized clonal pancreatic beta-cells. 140 Mar

A disruption of calcium homeostasis, leading to a sustained increase in cytosolic calcium levels, has been associated with cytotoxicity in response to a variety of agents in different cell types. We have observed that administration of a single high dose or multiple lower doses of the carcinogenic nephrotoxin ochratoxin A (OTA) to rats resulted in an increase of the renal cortex endoplasmic reticulum ATP-dependent calcium pump activity. The increase was very rapid, being evident within 10 min of OTA administration and remained elevated for at least 6 hr thereafter. The increase in calcium pump activity was inconsistent with previous observations that OTA enhances lipid peroxidation (ethane exhalation) in vivo, a condition known to inhibit the calcium pump. However, no evidence of enhanced lipid peroxidation was observed in the renal cortex since levels of malondialdehyde and a variety of antioxidant enzymes including catalase, DT-diaphorase, superoxide dismutase, glutathione peroxidase, glutathione reductase and glutathione S-transferase were either unaltered or reduced. In in vitro studies, addition of OTA to cortex microsomes during calcium uptake inhibited the uptake process although the effect was reversible. Preincubation of microsomes with NADPH had a profound inhibitory effect on calcium uptake but inclusion of OTA was able to reverse the inhibition. Changes in the rates of microsomal calcium uptake correlated with changes in the steady-state levels of the phosphorylated Mg2+/Ca(2+)-ATPase intermediate, suggesting that in vivo/in vitro conditions were affecting the rate of enzyme phosphorylation.
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PMID:Alterations in ATP-dependent calcium uptake by rat renal cortex microsomes following ochratoxin A administration in vivo or addition in vitro. 141 61

We have sequenced a gene that encodes a 377 amino acid putative protein with an ATPase motif typical of the protein family including SEC18p (NSF = N-ethyl maleimide-sensitive fusion protein; vesicle-mediated endoplasmic reticulum to Golgi protein transfer), PAS1p (peroxisome assembly), CDC48p (VCP = valosin-containing protein; cell cycle) and TBP1 (Tat-binding protein). This gene, AFG1 for ATPase family gene, also has substantial homology to these proteins outside the ATPase domain. AFG1 is located on chromosome V immediately centromere-proximal to MAK10.
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PMID:AFG1, a new member of the SEC18-NSF, PAS1, CDC48-VCP, TBP family of ATPases. 144 55

Endothelin (ET) and GnRH act through specific receptors to promote Ca2+ mobilization and influx pathways in pituitary gonadotrophs. In the present study cytoplasmic calcium ([Ca2+]i) and secretory responses to these two agonists are compared. In single gonadotrophs, low concentrations of both agonists cause oscillatory [Ca2+]i responses after a latent period. Such responses usually consist of discrete transients arising from the normal resting level, but are sometimes super-imposed on an elevated basal calcium level. At high doses, ET-1 and GnRH induce biphasic responses, composed of a spike phase followed by a plateau that often shows high frequency and low amplitude Ca2+ transients. The duration of the latent period and the frequency of the subsequent oscillations are correlated, and both are dependent on agonist concentration. The frequencies and amplitudes of Ca2+ spiking are also interrelated; increases in frequency are followed by more rapid decreases in the amplitude of the Ca2+ transients. After K(+)-induced depolarization, gonadotrophs retain their oscillatory Ca2+ responses to ET-1 and GnRH, with the same frequency as controls. Activation of protein kinase-C by phorbol esters does not alter the frequency of ET-induced Ca2+ transients, but significantly reduces their amplitudes. In contrast, treatment with nanomolar concentrations of thapsigargin converts ET-induced oscillations into a biphasic response, suggesting that Ca(2+)-ATPase in the endoplasmic reticulum participates in the oscillatory mechanism. The two agonists differ in their threshold doses and concentration dependence, ET being significantly less potent than GnRH. Also, gonadotrophs stimulated by ET-1 exhibit different post-treatment responsiveness than those exposed to GnRH. While GnRH-treated cells recover their full [Ca2+]i and secretory responses within 30 min as well as normal [Ca2+]i and secretory responses to ET-1, endothelin-treated cells are refractory to further stimulation with ET and exhibit either attenuated or enhanced Ca2+ and LH responses to GnRH, depending on the duration of exposure to ET-1 and the subsequent recovery period. These data indicate that both receptors use the same mechanism(s) for Ca2+ release, but have different capacities to generate, maintain, and reinitiate the Ca2+ signal.
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PMID:Differential actions of endothelin and gonadotropin-releasing hormone in pituitary gonadotrophs. 144 20


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