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  • 1
    Electronic Resource
    Electronic Resource
    Possible role of phospholipase C in the induction of Ca2+-paradox in rat heart (1993)
    Springer
    Molecular and cellular biochemistry 121 (1993), S. 181-190 
    Details
    ISSN: 1573-4919
    Keywords: phosphoinositide pathway ; phospholipase C ; Ca2+-paradox ; heart membranes ; alpha-adrenergic receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In order to investigate the involvement of phosphoinositide-specific phospholipase C (PLC), an enzyme associated with phosphoinositide signal transduction pathway, for the occurrence of Ca2+-paradox (loss of contractile activity associated with contracture), rat hearts perfused with Ca2+-free medium (1 to 5 min) were reperfused (5 to 10 min) with medium containing 1.25 mM Ca2+. Crude membranes isolated from hearts perfused with Ca2+-free medium exhibited a significantly increased activity of PLC, whereas normal activity was detected in hearts reperfused with Ca2+-containing medium. A significant rise in PLC activity was observed at 1 min of Ca2+-free perfusion; maximal increase was seen at 4 min of Ca2+-free perfusion. Minimal concentration of Ca2+ in the perfusion medium required for showing an increase in PLC activity was 10 μM, whereas that required for the occurrence of Ca2+-paradoxic changes in heart function upon reperfusion was 50μM. Perfusion of the hearts with Ca2+-free medium in the presence of low Na+ or at low temperature, which prevents the occurrence of Ca2+-paradox upon reperfusion, did not prevent the increase in PLC activity. An increase during Ca2+-free perfusion similar to that seen for PLC was also observed for two other enzymes, namely the phosphatidylinositol (PI) 4-kinase and the PI-4-monophosphate (PIP) 5-kinase, which synthesize the PLC substrate, phosphatidylinositol 4,5-bisphosphate (PIP2). No alteration of the alpha-adrenoreceptors was observed after 5 min of Ca2+-free perfusion. On the other hand, the observed changes in PLC activity during Ca2+-free perfusion appear to be due to some redistribution of the enzyme in the myocardium. These results suggest a possible role of the phosphoinositide/PLC pathway in the induction of Ca2+-paradox via mechanisms which do not appear to be associated with changes in the characteristics of alpha-adrenergic receptors. (Mol Cell Biochem121: 181–190, 1993)
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00925978
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  • 2
    Electronic Resource
    Electronic Resource
    The substrate specificity of phosphoinositide phospholipase C in rat heart sarcolemma (1992)
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 27-31 
    Details
    ISSN: 1573-4919
    Keywords: phospholipase C ; phosphoinositides ; phosphatidylinositol 4,5-bisphosphate ; phosphatidylinositol 4-phosphate ; rat heart ; sarcolemma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract In rat cardiac sarcolemmal membranes a phosphoinositide-specific phospholipase C (PLC) was found to be present. The enzyme hydrolysed exogenous [3H-]phosphatidylinositol 4,5-biphosphate ([3H-]PtdIns(4,5)P 2) in an optimized assay mixture containing 15 leg SL protein, 100 mM NaCl, 1 mM free Ca2+,14 mM Na-cholate and 20 AM [3H-]PtdIns (4,5)P 2 (400–500 dpm/gm-l) in 30 mM HEPES-Tris buffer (pH 7.0). The average specific activity was 9.14±0.55 nmol-mg−1·2.5 min−1. The addition of Mg2+ to the assay mixture did not change PLC activity but increased the relative amounts of dephosphorylated inositol products. In the absence of Na+ and at a low Ca2+ concentration (0.3 μM), Mg2+ also enhanced the intraSL levels of PtdIns4P and PtdIns, and, moreover, inhibited PLC activity (IC50∼0.07 mM). PtdIns4P seemd to be a good substrate for the rat SL PLC (23.07 ± 1.57 nmol·mg−1·2.5 min−1) whereas PtdIns was hydrolysed at a very low rate (0.36 ± 0.08 nmol·mg−1·2.5 min−1). Unlike PtdIns(4,5)P 2, PLC-dependent PtdIns4P and PtdIns hydrolysis was not inhibited by Ca2+ concentrations over 1 mM. The possibility of distinct isozymes being responsible for the different hydrolytic activities is discussed. (Mol Cell Biochem116: 27–31, 1992).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01270565
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  • 3
    Electronic Resource
    Electronic Resource
    Phorbol ester and the actions of phosphatidylinositol 4,5-bisphosphate specific phospholipase C and protein kinase C in microsomes prepared from cultured cardiomyocytes (1991)
    Springer
    Molecular and cellular biochemistry 105 (1991), S. 37-47 
    Details
    ISSN: 1573-4919
    Keywords: cardiomyocytes ; microsomes ; phorbol ester ; phosphatidylinositol 4,5-bisphosphate ; phospholipase C ; protein kinase C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Microsomes were prepared from cultured neonatal rat cardiomyocytes. Incubation of microsomes in buffer containing 5µM CaCl2, 5 mM cholate and 100 nM [3H-]Phosphatidylinosito14,5-bisphosphate (PtdIns(4,5) P2) resulted in the formation of [3H-]InsP 3. GTP-gamma-S (125 µM) stimulated the production of [3H-]InsP 3. Microsomes prepared from phorbol ester-treated (100 nM phorbol 12-myristate 13-acetate, PMA) cardiomyocytes showed decreased activities of basal as well as GTP-gamma-S-stimulated [3H-]Ptdlns(4,5)P 2 hydrolysis. In the microsomes a 15 kD protein was demonstrated to be the major substrate phosphorylated by intrinsic protein kinase C, which was activated by 0.5 mM Ca2+. Addition of phorbol ester (100 nM PMA) enhanced the 32P-incorporation into the 15 kD protein. Protein kinase C, purified from rat brain, in the presence of Ca2+, diglyceride, and phosphatidylserine did not change the phosphorylation pattern any further. In conclusion, it was shown that phorbol ester pretreatment of neonatal rat cardiomyocytes reduces microsomel GTP-gamma-S-stimulated Ptdlns(4,5)P 2-specific phospholipase C activity, as estimated with exogenous substrate, and that in cardiomyocyte microsomes phorbol ester activates protein kinase C-induced 15 kD protein phosphorylation. The results indicate that phorbol ester may down-regulate α-adrenoceptor mediated Ptdlns(4,5)P 2 hydrolysis by activation of protein kinase C-induced 15 kD protein phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00230373
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