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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 116 (1992), S. 125-129 
    ISSN: 1573-4919
    Keywords: fatty acid ; carnitine ; smooth muscle ; endothelium ; ischemia ; heart ; skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Vascular endothelial and -smooth muscle cells have been shown to use fatty acids as substrates for oxidative phosphorylation. Endothelial cells are more vulnerable to oxidative stress than muscle cells and are prone to loose carnitine early during hypoperfusion. This has been suggested by two observations. The first is that incubation of isolated endothelial cells in a low carnitine medium leads to oleate oxidation, dependent upon carnitine addition, whereas smooth muscle cells do not depend on carnitine addition duringin vitro incubation, although aminocarnitine, a specific inner-membrane carnitine palmitoyltransferase inhibitor, inhibits fatty acid oxidation. The second observation is that rat hearts labeledin vivo with14C-carnitine loose, as paced Langendorff heart, only 4% of their carnitine in 20 min perfusion, following 60 min global ischemia. The carnitine released had a much higher specific radioactivity than the carnitine that was not released. It indicates compartmentation of carnitine in heart. As earlier and presently discussed work shows endothelial vulnerability, it is to be expected that this cell type may become carnitine deficient during pacing and ischemia. Endothelial incompetence in flow regulation could be delaved by the presence of carnitine and fatty acids in pre-ischemia. It is speculated how activated fatty acids could protect endothelium.
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Molecular and cellular biochemistry 88 (1989), S. 129-137 
    ISSN: 1573-4919
    Keywords: myocardial lipid metabolism ; normoxia ; ischemia ; regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Fatty acids, the preferred substrate in normoxic myocardium, are derived from either exogenous or endogenous triacylglycerols. The supply of exogenous fatty acids is dependent of the rate of lipolysis in adipose tissue and of the lipoprotein lipase activity at the coronary vascular endothelium. A large part of the liberated fatty acids is reesterified with glycerol-3-phosphate and converted to triacylglycerols. Endogenous lipolysis and lipogenesis are intracellular compartmentalized multienzyme processes of which individual hormone-sensitive steps have been demonstrated in adipose tissue. The triacylglycerol lipase is the rate-limiting enzyme of lipolysis and glycerol-3-phosphate acyltransferase and possibly phosphatidate phosphohydrolase are the rate-limiting enzymes of lipogenesis. The hormonal regulation of both processes in heart is still a matter of dispute. Triacylglycerol lipase activity in myocardial tissue has two intracellular sources: 1, the endoplasmic reticular and soluble neutral lipase, and 2. the lysosomal acid lipase. Studies in our laboratory have indicated that whereas lipolysis is enhanced during global ischemia and anoxia, overall lipolytic enzyme activities in heart homogenates were not altered. In addition we were unable to demonstrate alterations in tissue triacylglycerol content and glycerol-3-phosphate acyltransferase activity under these conditions. Lipolysis, is subject to feedback inhibition by product fatty acids. Therefore all processes leading to an increased removal of fatty acids from the catalytic site of the lipase will stimulate lipolysis. These studies will be reviewed. In addition, studies from our department have demonstrated the capacity of myocardial lysosomes to take up and degrade added triacylglycerol-particles in vitro. Such a process, stimulated by Ca2+ and stimulated by acidosis, offers another physiological target for hormone actions.
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