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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
    Inhibition of (Na/K)-ATPase by electrophilic substances: Functional implications (1995)
    Springer
    Molecular and cellular biochemistry 147 (1995), S. 187-192 
    Details
    ISSN: 1573-4919
    Keywords: (Na/K)-ATPase ; electrophilic reagents ; cation binding site ; isolated perfused heart ; 5-nitrofurylethylene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The effect of electrophilic substances: p-bromophenylisothiocyanate (PBITC); fluoresceinisothiocyanate (FITC); [4-isothiocyanatophenyl-(6-thioureidohexyl)-carbamoylmethyl]-ATP (ATPITC); 2,4,6-trinitrobezenesulfonic acid (TNBS); 1-(5-nitro-2-furyl)-2-phenylsulfonyl-2-furylcarbonyl ethylene (FE1); 1-(5-phenylsulfonyl-2-furyl)-2-phenylsulfonyl-2-furylcarbonyl ethylene (FE2) and 1-(5-phenylsulfonyl-2-furyl)-2-phenylsulfonyl-2-tienocarbonyl ethylene (FE3) on the sarcolemmal (Na/K)-ATPase isolated from guinea-pig hearts was studied. FITC and PBITC were found to inhibit competitively the activation of (Na/K)-ATPase by ATP. Being for the enzyme inhibitor and substrate at the same time ATPITC does not offered clear kinetic behavior. However, the activation of (Na/K)-ATPase by sodium and potassium ions was inhibited non-competitively by all three isothiocyanates. These data indicated that isothiocyanates may interact predominantly in the ATP-binding site of the enzyme molecule. In contrary to isothiocyanates TNBS and FE1 (FE2 and FE3 were ineffective) inhibited the activation of (Na/K)-ATPase by ATP non-competitively i.e., their interaction in the ATP-binding site seemed to be improbable. Nevertheless, TNBS and FE1 both manifested affinities to that moiety of (Na/K)-ATPase molecule which is binding potassium. More specific was the effect of FE1 that showed clearly competitive inhibition of potassium-stimulation of the enzyme activity. FE1 exerted also an ouabain-like effect on the mechanical activity of isolated perfused guinea-pig heart. This result indicates that FE1 seems to exert a selective inhibition of the (Na/K)-ATPase not only in vitro but also in integrated cardiac tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00944800
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    Paper (German National Licenses)
    Fulltext
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