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Are annexins involved in cardiac phospolipid metabolism?
,I Mel Cell Cardiol
23 (Supplement
V) (1991)
139
ARE ANNEXINS INVOLVED IN CARDIAC PHOSPCILIPID METABCLISM? Marc van Bilsen’, Chris P.M. Reutelinqsperger*, Ger J. van der Vussel, Depts. of Physiology1 and Biochemistry*~ Cardiovascular Research In&ute,Maastdcht, Univ. of timburg, the Neihertands. -Stimulation of cardiac phospholipld (PL) metabolism has diverse btobacal effects. Receptor-mediated stimulation of cardiac phospholipases (PLAses) often involves GTP-binding proteins, and leads to the production of biologically active products (arachidontc acid, diecyfglycerof). Uncontrolied degradation of PLs is considered to play a pivotal rol in the sequence of events leading to irreversible cell damage during myocardial ischemia and reperfusion. In general, the mechanfsms controlling the activity of PLAses are poorfy understood. A modulatory function of annexins in the control of PL metabolism has been proposed. The presence of annexins in a variety of tissues, among which heart tissue, has been demonstrated. The annexins represent a family of structuralfy related proteins that interact witfr PL bilayers in a caicfum dependent manner. Annexin V is known to be the most abundant annexin lound in the heart. The availability of large amounts of human recombinant Annexin V (Annexin V,) enabled us to study the effect of this annexin on cardiac PL metabolism. The in vitro experiments indicate that Annexin Vr signffllntfy inhibits the activitiy of cardiac membrane-bound PLAses, acting on their natural surrounding substrate, in a calcium-dependent manner. Interestingly, the distdbutiin of annexins in the heart is cell type specfffc, suggesting a cell-type speciffc function of these proteins in the heart. For instance, western blot analysis showed that annexin V is confined to non-myocytes, i.e. endothelial and fibroblast-like cells. The absence of Annexin V in cardiac myocytes dismisses an important role in cardfomyocyte phospholipfd metabolism. The presence of relatively large amounts of Annexin V in endothefial cells raises questions as to the physiological significance of this protein, especially in relation to its potent effects on phospholipid hydrolysis, in this cell-type.
140 . .-
FISH OIL ADMINISTRATION AND MEMBRANE LIPID PEROXIDATION STATUS IN RAT HEART Gilles Nalbone, Magali Chautan, Raymond Calaf’, Jeannie Leonardi and Huguette Lafont, INSERMU130, 18 Av. Mozart 13009 Marseille. ‘Laboratoire de Biochimie. Faculte de Pharmacie , Marseille, FRANCE. The effect of dietary n-6/n-3 fatty acid ratio on heart fatty acid composition and peroxfdation status was investigated in rats fed diets containing fat (17% w/w) in which the n-6/n-3 ratio varied from 50 to 0.8 but keeping constant the P/S ratio. The two major classes of heart phospholipids (phosphatidylcholine and phosphatidylethanolamine) showed a considerable enrichment in docosahexaenoic acid (DHA) and a drastic decrease in arachidonic acid (AA). This was due in part to the kinetic properties of acyl-CoA synthetase toward DHA which competitively inhibits the thioesterification of AA and consequently the AA incorporation into phosphatidylcholine. The most striking effect observed, was a considerable a-tocopherol enrichment (x4) of heart membranes as they became enriched in DHA and EPA. Accordingly, a strong positive correlation was found between heart a-tocopherol and DHA levels (r= 0.86, p~O.0001) and DHA plus EPA levels (r= 0.84, p?;O.O003. Conversely, the liver a-tocopherol content dropped dramatically as n-3 PUFA were gradually added to the diets. The increase in heart a-tocopherol was not the consequence of a higher delivery of a-tocopherol by plasma lipoproteins since n-3 fatty acids led to a decrease in plasma a-tocopherol which was in fact the result of the decrease in circulating lipids. It is suggested that heart efficiently protects its membrane system against peroxidation by “adapting” its a-tocopherol content to diet-induced changes in membrane n-3 very long chain PUFA content.
141 PHASE TRANSITION
IN CARDIAC MEMBRANE
UPON ISCHEMIA
A.J. Verkleij Department of Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utmcht, The Netherhnds To survive ischemia, teperhtsion is essential. However, if the period of ischemia is too long, reperfusion leads to Ca*’ overload and an irreversible uncoupling of excitation/contraction and sarcolemma damage. The question is what determines the irreversibility of this condition. At the sarcolemma level, them are three alterations which occur at the edge of the irreversible ischemic condition. (i) Clustering of intramembraneous particles, which suggests reorganization in the lateral dianibution of the phospholipids; (ii) detachment of the cytoskeleton from the sarcolemma, and (hi) loss of Ca” from the satcolemma which both suggest a loss in lipid asymmetry. The possible factors for these changes in the sarcolemma, such as acidosis, loss of high energy phosphates and the increase of natural amphiphiks will be discussed. s.51
23 (Supplement
V) (1991)
139
ARE ANNEXINS INVOLVED IN CARDIAC PHOSPCILIPID METABCLISM? Marc van Bilsen’, Chris P.M. Reutelinqsperger*, Ger J. van der Vussel, Depts. of Physiology1 and Biochemistry*~ Cardiovascular Research In&ute,Maastdcht, Univ. of timburg, the Neihertands. -Stimulation of cardiac phospholipld (PL) metabolism has diverse btobacal effects. Receptor-mediated stimulation of cardiac phospholipases (PLAses) often involves GTP-binding proteins, and leads to the production of biologically active products (arachidontc acid, diecyfglycerof). Uncontrolied degradation of PLs is considered to play a pivotal rol in the sequence of events leading to irreversible cell damage during myocardial ischemia and reperfusion. In general, the mechanfsms controlling the activity of PLAses are poorfy understood. A modulatory function of annexins in the control of PL metabolism has been proposed. The presence of annexins in a variety of tissues, among which heart tissue, has been demonstrated. The annexins represent a family of structuralfy related proteins that interact witfr PL bilayers in a caicfum dependent manner. Annexin V is known to be the most abundant annexin lound in the heart. The availability of large amounts of human recombinant Annexin V (Annexin V,) enabled us to study the effect of this annexin on cardiac PL metabolism. The in vitro experiments indicate that Annexin Vr signffllntfy inhibits the activitiy of cardiac membrane-bound PLAses, acting on their natural surrounding substrate, in a calcium-dependent manner. Interestingly, the distdbutiin of annexins in the heart is cell type specfffc, suggesting a cell-type speciffc function of these proteins in the heart. For instance, western blot analysis showed that annexin V is confined to non-myocytes, i.e. endothelial and fibroblast-like cells. The absence of Annexin V in cardiac myocytes dismisses an important role in cardfomyocyte phospholipfd metabolism. The presence of relatively large amounts of Annexin V in endothefial cells raises questions as to the physiological significance of this protein, especially in relation to its potent effects on phospholipid hydrolysis, in this cell-type.
140 . .-
FISH OIL ADMINISTRATION AND MEMBRANE LIPID PEROXIDATION STATUS IN RAT HEART Gilles Nalbone, Magali Chautan, Raymond Calaf’, Jeannie Leonardi and Huguette Lafont, INSERMU130, 18 Av. Mozart 13009 Marseille. ‘Laboratoire de Biochimie. Faculte de Pharmacie , Marseille, FRANCE. The effect of dietary n-6/n-3 fatty acid ratio on heart fatty acid composition and peroxfdation status was investigated in rats fed diets containing fat (17% w/w) in which the n-6/n-3 ratio varied from 50 to 0.8 but keeping constant the P/S ratio. The two major classes of heart phospholipids (phosphatidylcholine and phosphatidylethanolamine) showed a considerable enrichment in docosahexaenoic acid (DHA) and a drastic decrease in arachidonic acid (AA). This was due in part to the kinetic properties of acyl-CoA synthetase toward DHA which competitively inhibits the thioesterification of AA and consequently the AA incorporation into phosphatidylcholine. The most striking effect observed, was a considerable a-tocopherol enrichment (x4) of heart membranes as they became enriched in DHA and EPA. Accordingly, a strong positive correlation was found between heart a-tocopherol and DHA levels (r= 0.86, p~O.0001) and DHA plus EPA levels (r= 0.84, p?;O.O003. Conversely, the liver a-tocopherol content dropped dramatically as n-3 PUFA were gradually added to the diets. The increase in heart a-tocopherol was not the consequence of a higher delivery of a-tocopherol by plasma lipoproteins since n-3 fatty acids led to a decrease in plasma a-tocopherol which was in fact the result of the decrease in circulating lipids. It is suggested that heart efficiently protects its membrane system against peroxidation by “adapting” its a-tocopherol content to diet-induced changes in membrane n-3 very long chain PUFA content.
141 PHASE TRANSITION
IN CARDIAC MEMBRANE
UPON ISCHEMIA
A.J. Verkleij Department of Molecular Cell Biology, University of Utrecht, Padualaan 8, 3584 CH Utmcht, The Netherhnds To survive ischemia, teperhtsion is essential. However, if the period of ischemia is too long, reperfusion leads to Ca*’ overload and an irreversible uncoupling of excitation/contraction and sarcolemma damage. The question is what determines the irreversibility of this condition. At the sarcolemma level, them are three alterations which occur at the edge of the irreversible ischemic condition. (i) Clustering of intramembraneous particles, which suggests reorganization in the lateral dianibution of the phospholipids; (ii) detachment of the cytoskeleton from the sarcolemma, and (hi) loss of Ca” from the satcolemma which both suggest a loss in lipid asymmetry. The possible factors for these changes in the sarcolemma, such as acidosis, loss of high energy phosphates and the increase of natural amphiphiks will be discussed. s.51