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Sarcoplasmic Reticulum Ca2+ (sarcoplasmic + reticulum_ca2+)
Selected AbstractsNo relationship between enzyme activity and structure of nucleotide binding site in sarcoplasmic reticulum Ca2+ -ATPase from short-term stimulated rat muscleACTA PHYSIOLOGICA, Issue 4 2009T. Mishima Abstract Aim:, We examined whether structural alterations to the adenine nucleotide binding site (ANBS) within sarcoplasmic (endo) reticulum Ca2+ -ATPase (SERCA) would account for contraction-induced changes in the catalytic activity of the enzyme as assessed in vitro. Methods:, Repetitive contractions were induced in rat gastrocnemius by electrical nerve stimulation. Measurements of sarcoplasmic reticulum properties were performed on control and stimulated muscles immediately after or at 30 min after the cessation of 5-min stimulation. In order to examine the properties at the ANBS, the binding capacity of SERCA to fluorescence isothiocyanate (FITC), a competitive inhibitor at the ANBS, was analysed in microsomes. Results:, Short-term electrical stimulation evoked a 23.9% and 32.6% decrease (P < 0.05) in SERCA activity and in the FITC binding capacity, respectively, in the superficial region of the muscle. Whereas SERCA activity reverted to normal levels during 30-min recovery, a restoration of the FITC binding capacity did not occur. Conclusion:, The discordant changes between the enzyme activity and the FITC binding suggest that, at least during recovery after exercise, changes in SERCA activity may not correlate closely with structural alterations to the ANBS within the enzyme. [source] Modulation of sarcoplasmic reticulum Ca2+ -ATPase by chronic and acute exposure to peroxynitriteFEBS JOURNAL, Issue 13 2004Yolanda Gutiérrez-Martín The Ca2+ -ATPase of skeletal muscle sarcoplasmic reticulum (SERCA), an integral membrane protein, becomes irreversibly inactivated in vitro by the addition of a single bolus of peroxynitrite with a K0.5 of 200,300 µm, and this results in a large decrease of the ATP-dependent Ca2+ gradient across the sarcoplasmic reticulum (SR) membranes. The inactivation of SERCA is raised by treatment of SR vesicles with repetitive micromolar pulses of peroxynitrite. The inhibition of the SERCA is due to the oxidation of thiol groups and tyrosine nitration. Scavengers that react directly with peroxynitrite, such as cysteine, reduced glutathione, NADH, methionine, ascorbate or Trolox, a water-soluble analog of ,-tocopherol, afforded significant protection. However, dimethyl sulfoxide and mannitol, two hydroxyl radical scavengers, and ,-tocopherol did not protect SERCA from inactivation. Our results showed that the target of peroxynitrite is the cytosolic globular domain of the SERCA and that major skeletal muscle intracellular reductants (ascorbate, NADH and reduced glutathione) protected against inhibition of this ATPase by peroxynitrite. [source] Modeling the three-dimensional structure of H+ -ATPase of Neurospora crassaFEBS JOURNAL, Issue 21 2002Proposal for a proton pathway from the analysis of internal cavities Homology modeling in combination with transmembrane topology predictions are used to build the atomic model of Neurospora crassa plasma membrane H+ -ATPase, using as template the 2.6 Å crystal structure of rabbit sarcoplasmic reticulum Ca2+ -ATPase [Toyoshima, C., Nakasako, M., Nomura, H. & Ogawa, H. (2000) Nature 405, 647,655]. Comparison of the two calcium-binding sites in the crystal structure of Ca2+ -ATPase with the equivalent region in the H+ -ATPase model shows that the latter is devoid of most of the negatively charged groups required to bind the cations, suggesting a different role for this region. Using the built model, a pathway for proton transport is then proposed from computed locations of internal polar cavities, large enough to contain at least one water molecule. As a control, the same approach is applied to the high-resolution crystal structure of halorhodopsin and the proton pump bacteriorhodopsin. This revealed a striking correspondence between the positions of internal polar cavities, those of crystallographic water molecules and, in the case of bacteriorhodopsin, the residues mediating proton translocation. In our H+ -ATPase model, most of these cavities are in contact with residues previously shown to affect coupling of proton translocation to ATP hydrolysis. A string of six polar cavities identified in the cytoplasmic domain, the most accurate part of the model, suggests a proton entry path starting close to the phosphorylation site. Strikingly, members of the haloacid dehalogenase superfamily, which are close structural homologs of this domain but do not share the same function, display only one polar cavity in the vicinity of the conserved catalytic Asp residue. [source] NO message from muscleMICROSCOPY RESEARCH AND TECHNIQUE, Issue 3 2001Zarko Grozdanovic Abstract The synthesis of the free radical gas nitric oxide (NO) is catalyzed by the enzyme NO synthase (NOS). NOS converts arginine and molecular oxygen to NO and citrulline in a reaction that requires NADPH, FAD, FMN, and tetrahydrobiopterin as cofactors. Three types of NOS have been identified by molecular cloning. The activity of the constitutively expressed neuronal NOS (nNOS) and endothelial NOS (eNOS) is Ca2+/calmodulin-dependent, whereas that the inducible NOS (iNOS) is Ca2+ -insensitive. The predominant NOS isoform in skeletal muscle is nNOS. It is present at the sarcolemma of both extra- and intrafusal muscle fibers. An accentuated accumulation of nNOS is found in the endplate area. This strict sarcolemmal localization of nNOS is due its association with the dystrophin-glycoprotein complex, which is mediated by the syntrophins. The activity of nNOS in skeletal muscle is regulated by developmental, myogenic, and neurogenic influences. NO exerts several distinct effects on various aspects of skeletal muscle function, such as excitation-contraction coupling, mitochondrial energy production, glucose metabolism, and autoregulation of blood flow. Inside the striated muscle fibers, NO interacts directly with several classes of proteins, such as soluble guanylate cyclase, ryanodine receptor, sarcoplasmic reticulum Ca2+ -ATPase, glyceraldehyde-3-phosphate dehydrogenase, and mitochondrial respiratory chain complexes, as well as radical oxygen species. In addition, NO produced and released by contracting muscle fibers diffuses to nearby arterioles where it acts to inhibit reflex sympathetic vasoconstriction. Microsc. Res. Tech. 55:148,153, 2001. © 2001 Wiley-Liss, Inc. [source] Junctin and the histidine-rich Ca2+ binding protein: potential roles in heart failure and arrhythmogenesisTHE JOURNAL OF PHYSIOLOGY, Issue 13 2009Tracy J. Pritchard Contractile dysfunction and ventricular arrhythmias associated with heart failure have been attributed to aberrant sarcoplasmic reticulum (SR) Ca2+ cycling. The study of junctin (JCN) and histidine-rich Ca2+ binding protein (HRC) becomes of particular importance since these proteins have been shown to be critical regulators of Ca2+ cycling. Specifically, JCN is a SR membrane protein, which is part of the SR Ca2+ release quaternary structure that also includes the ryanodine receptor, triadin and calsequestrin. Functionally, JCN serves as a bridge between calsequestrin and the Ca2+ release channel, ryanodine receptor. HRC is a SR luminal Ca2+ binding protein known to associate with both triadin and the sarcoplasmic reticulum Ca2+ -ATPase, and may thus mediate the crosstalk between SR Ca2+ uptake and release. Indeed, evidence from genetic models of JCN and HRC indicate that they are important in cardiophysiology as alterations in these proteins affect SR Ca2+ handling and cardiac function. In addition, downregulation of JCN and HRC may contribute to Ca2+ cycling perturbations manifest in the failing heart, where their protein levels are significantly reduced. This review examines the roles of JCN and HRC in SR Ca2+ cycling and their potential significance in heart failure. [source] Mapping nucleotide binding site of calcium ATPase with IR spectroscopy: Effects of ATP ,-phosphate bindingBIOPOLYMERS, Issue 4-5 2002Man Liu Abstract The changes in the IR spectra of the sarcoplasmic reticulum Ca2+ -ATPase upon nucleotide binding are recorded in H2O at 1°C in different buffers [imidazole, methylimidazole, 3-(N -morpholino)propanesulfonic acid, and phosphate] at different pH values (pH 6.5,7.8). The difference spectra of nucleotide binding are sensitive to the composition of the solvent. With methylimidazole at pH 7.5 providing the largest binding-induced signals, the effects of ,-phosphate binding are investigated using ATP, ADP, and ,,,-iminoadenosine 5,-triphosphate. The ,-phosphate contributes ,20% to the conformational change seen by IR spectroscopy and affects the ,-sheet structures. The IR experiments also reveal the known affinity difference between ADP and ATP. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 67: 267,270, 2002 [source] Effect of letrozole on urinary bladder function in the female rabbitBJU INTERNATIONAL, Issue 6 2007Wei-Yu Lin OBJECTIVE To investigate the effect of letrozole (a potent aromatase inhibitor that effectively inhibit the synthesis of oestrogen) on bladder contraction with changes in morphology and biochemistry. MATERIALS AND METHODS Sixteen female New Zealand white rabbits were separated into four equal groups; groups 1,3 were given oral letrozole for 1, 2 and 3 weeks, and group 4 was given saline and served as the control group. At the end of the medication period each rabbit was anaesthetized and the bladder muscle strips were used for contractile, histological and biochemical studies. RESULTS The concentration of serum oestrogen was significantly lower and testosterone was significantly higher in letrozole-treated rabbits than in the control group. The rabbits treated for 1 week with letrozole showed significant decreases in the contractile responses to electrical field stimulation, ATP and carbachol, but not to KCl. Contractility returned to normal in the rabbits treated for 2 and 3 weeks. Letrozole resulted in an increased volume percentage of collagens and decreased bladder compliance. The volume percentage of the smooth muscle component also changed, with a significant decrease at 1 week and then a gradual increase at 2 and 3 weeks. Contractile dysfunction was absent at 2 and 3 weeks, which was consistent with no change in sarcoplasmic reticulum Ca2+ -ATPase content or mitochondrial function. CONCLUSIONS The bladder contractility decline in the first week and was restored at 2 and 3 weeks. The present study unexpectedly showed the possibility that testosterone might be as important as oestrogen in the contractile function of the female bladder. [source] Modulation of protein kinase C by curcumin; inhibition and activation switched by calcium ionsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2007Y A Mahmmoud Background and purpose: Previous studies have identified the natural polyphenol curcumin as a protein kinase C (PKC) inhibitor. In contrast, we found significant stimulation of PKC activity following curcumin treatment. Thus, the mechanism of curcumin interaction with PKC was investigated. Experimental approach: We employed phosphorylation assays in the presence of soluble or membrane-bound PKC substrates, followed by SDS,PAGE, autoradiography and phosphorylation intensity measurements. Key results: Curcumin inhibited PKC in the absence of membranes whereas stimulation was observed in the presence of membranes. Further analysis indicated that curcumin decreased PKC activity by competition with Ca2+ stimulation of the kinase, resulting in inhibition of activity at lower Ca2+ concentrations and stimulation at higher Ca2+ concentrations. The role of the membrane is likely to be facilitation of Ca2+ -binding to the kinase, thus relieving the curcumin inhibition observed at limited Ca2+ concentrations. Curcumin was found to mildly stimulate the catalytic subunit of PKC, which does not require Ca2+ for activation. In addition, studies on Ca2+ -independent PKC isoforms as well as another curcumin target (the sarcoplasmic reticulum Ca2+ -ATPase) confirmed a correlation between Ca2+ concentration and the curcumin effects. Conclusions and Implications: Curcumin competes with Ca2+ for the regulatory domain of PKC, resulting in a Ca2+ -dependent dual effect on the kinase. We propose that curcumin interacts with the Ca2+ -binding domains in target proteins. To our knowledge, this is the first study that defines an interaction domain for curcumin, and provides a rationale for the broad specificity of this polyphenol as a chemopreventive drug. British Journal of Pharmacology (2007) 150, 200,208. doi:10.1038/sj.bjp.0706970 [source] | ||||||||||||||||