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Glycerolipid synthesis in heart cells

Swanton, Eileithyia Mara Serena; (1996) Glycerolipid synthesis in heart cells. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Isolated ventricular myocytes were used to study the glycerolipid synthesis process in the rat heart. The presence of the following lipogenic enzymes: fatty acyl-CoA synthetase (FAS), microsomal and mitochondrial forms of glycerolphosphate acyltransferase (GPAT), monoacylglycerolphosphate acyltransferase (MGPAT), phosphatidate phosphohydrolase (PAP)-1 and -2, and diacylglycerol acyltransferase (DGAT); was demonstrated in homogenates of ventricle muscle and cardiac myocytes. The specific activities of these enzymes were generally similar in the two preparations, with the exception of PAP-1 and -2 which were significantly lower in myocytes than in ventricle muscle. Further studies were undertaken to elucidate the nature of GPAT and PAP in ventricle muscle and compared with those of the more extensively characterised adipose tissue and liver enzymes. GPAT activity in the ventricle sarcoplasmic reticulum fraction had a 4-fold higher Km for glycerol-3-phosphate than GPAT in adipose tissue microsomes. Translocation of PAP-1 from a ventricle membrane fraction was demonstrated in response to lowering ionic strength. Incubation of myocytes with palmitate promoted translocation of PAP to membranes. PAP-2 in ventricle homogenates and membrane fractions was inhibited by physiological concentrations of Mg2+. A radioisotope pulse-chase protocol, established for use in perfused hearts, was adapted to measure glycerolipid turnover in isolated Ca2+-tolerant myocytes. The cells actively synthesised triacylglycerol (TAG) and phospholipids, and turned over their endogenous TAG pool so that oxidation of endogenous fatty acids occurred. Adrenaline increased TAG and phospholipid synthesis, stimulated lipolysis and endogenous fatty acid oxidation, but decreased oxidation of exogenous fatty acids. Adrenaline also stimulated microsomal GPAT activity and decreased association of PAP with myocyte membranes. Both α1- and β-adrenoceptor-mediated pathways appeared to be necessary for complete adrenergic stimulation of TAG synthesis, whilst α1-adrenergic stimulation was sufficient to fully mimic the inhibition of exogenous fatty acid oxidation. Insulin stimulated TAG but not phospholipid synthesis. Neither basal nor adrenaline-stimulated rates of lipolysis were inhibited by insulin. Increasing the concentration exogenous fatty acids enhanced utilisation of these substrates by myocytes, but suppressed the mobilisation and oxidation of endogenous fatty acids. The effects of adrenaline were apparent at all exogenous fatty acid concentrations examined.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Glycerolipid synthesis in heart cells
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Biological sciences; Glycerolipids
URI: https://discovery.ucl.ac.uk/id/eprint/10106029
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