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Short-term incubation of cardiac myocytes with isoprenaline has no effect on heparin-releasable or cellular lipoprotein lipase activity.

ABSTRACT: Heparin (5 units/ml) produced a rapid (5-10 min) release of lipoprotein lipase (LPL) into the incubation medium of cardiac myocytes. Preincubation of myocytes for 30 min with 0.01-10 microM-isoprenaline, 100 microM-forskolin or 500 microM-8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate did not increase heparin-releasable LPL activity. Incubation with isoprenaline also did not change cellular LPL activity, even though the catecholamine did increase the phosphorylase a activity ratio.

SUBMITTER: Severson DL

PROVIDER: S-EPMC1148534 | biostudies-other | 1987 Nov

REPOSITORIES: biostudies-other

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Treatment of cardiac myocytes with 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate, forskolin or cholera toxin does not stimulate cellular or heparin-releasable lipoprotein lipase activities.

Project description:Incubation of isolated cardiac myocytes with 500 microM-8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (CPT-cAMP) or 100 microM-forskolin for 2 1/2 h did not increase the heparin-induced release of lipoprotein lipase (LPL) into the medium. When LPL activity in cardiac myocytes was depleted by treatment of rats with cycloheximide (2 mg/kg; 2.5 h) and inclusion of the protein-synthesis inhibitor in the isolation solutions, incubation with CPT-cAMP or forskolin did not influence the rate of repletion of LPL activity in cells or the recovery of heparin-releasable LPL activity. Although the administration of cholera toxin (0.5 mg/kg; 16-17 h) to rats increased LPL activity in a low-speed supernatant fraction from heparin-perfused hearts, LPL activity was not increased in cardiac myocytes from cholera-toxin-treated rat hearts, and the heparin-induced release of LPL was unchanged. Incubation of cultured ventricular myocytes with 1 microgram of cholera toxin/ml or 500 microM-CPT-cAMP for 24 h did not increase cellular LPL activity or LPL released into the culture medium after a 40 min incubation with heparin. Therefore interventions that stimulate adenylate cyclase activity (forskolin, cholera toxin) or incubation with CPT-cAMP do not increase cellular LPL activity or promote the translocation of LPL to a heparin-releasable fraction in cardiac myocytes.

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The storage and synthetic pools of heparin-releasable lipoprotein lipase and hepatic triacylglycerol lipase in the growing puppy.

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Heparin-releasable lipase activity of rat adrenals, ovaries and testes.

Project description:The presence of NaCl-resistant, neutral triacylglycerol hydrolase (lipase) activity in rat adrenal gland, ovary and testis was studied. Both adrenals and ovaries but not testes were found to contain such a lipase. The activity of the enzyme in the adrenal gland was lowered during cortisol treatment and hypothyroidism. An elevated adrenal lipase activity was found during hyperthyroidism. Pseudo-pregnant and lactating rats had higher ovarian lipase activities than cyclic rats. Ovarian lipase activity in lactating rats was positively correlated with the serum concentrations of progesterone and of 20 alpha-hydroxyprogesterone and negatively correlated with the high-density-lipoprotein non-esterified cholesterol concentration. The lipase activity of adrenals and of ovaries was largely releasable from these organs by heparin and could be inhibited by an antibody against heparin-releasable liver lipase. This indicated that the lipase is extracellularly located and is similar to 'liver' lipase. A possible role of this lipase in adrenals and ovaries is discussed.

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Localization of the heparin-releasable lipase in situ in the rat liver.

Project description:Immunofluorescence and immuno-electron microscopy were used for the localization of the heparin-releasable lipase in situ in the rat liver. The lipase is located exclusively on the liver endothelial cells. No labelling could be detected on the parenchymal of Kupffer cells, or in the livers of heparin-pretreated animals. The physiological significance of the endothelial localization of the hepatic lipase is discussed.

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Rapid effects of isoprenaline, glucagon, pacing and potassium arrest on post-heparin lipoprotein lipase activity in the perfused rat heart.

Project description:The amount of lipoprotein lipase activity released by heparin into the perfusion medium of isolated rat hearts could be increased within 60s by isoprenaline, glucagon or pacing. Potassium arrest and propranolol inhibited the effects of isoprenaline and pacing respectively.

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Complete loss of heparin-releasable triacylglycerol lipase activity after collagenase treatment of the rat liver.

Project description:Lipolytic activity at pH 8.5-9.5 was lowered by approx. 80% in homogenates from livers perfused with collagenase or heparin. No heparin-releasable lipase activity was detected in hepatocytes isolated by collagenase treatment. It is concluded that crude collagenase completely inactivates the plasma-membrane-bound heparin-releasable lipase.

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Structure of heparin fragments with high affinity for lipoprotein lipase and inhibition of lipoprotein lipase binding to alpha 2-macroglobulin-receptor/low-density-lipoprotein-receptor-related protein by heparin fragments.

Project description:Heparin-derived deca- and octa-saccharides were subjected to affinity chromatography on lipoprotein lipase-Sepharose and the fractions eluted at high salt concentration were analysed by strong-anion-exchange chromatography. Two high-affinity decasaccharides were isolated and the structure determined by one- and two-dimensional 1H-n.m.r. spectroscopy. The affinities of 3H-labelled low-molecular-mass heparin and size-fractionated deca-, octa-, and hexa-saccharides for lipoprotein lipase immobilized on microtitre plates were determined from saturation curves. From competition experiments the affinities of unlabelled heparins and pure deca- and hexa-saccharide fragments were determined. The binding was size- and charge-dependent, but structural dependency was also indicated. Thus substitution of a 2-O-sulphated L-iduronic acid with D-glucuronic acid was less important than the sulphation pattern of the D-glucosamine residue for affinity for lipoprotein lipase. Heparin inhibits binding of lipoprotein lipase to alpha 2-macroglobulin-receptor/low-density-lipoprotein receptor-related protein. The effects of size, charge and structure for this inhibition were studied. The ability of the heparin fragments to inhibit binding correlated with their affinity for lipoprotein lipase. This indicates that the inhibition of the binding of lipoprotein lipase to alpha 2-macroglobulin-receptor/low-density-lipoprotein receptor-related protein by heparin is exclusively mediated by binding of heparin to lipoprotein lipase.

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Interaction of lipoprotein lipase with native and modified heparin-like polysaccharides.

Project description:1. Lipoprotein lipase (EC 3.1.1.34), which was previously shown to bind to immobilized heparin, was now found to bind also to heparan sulphate and dermatan sulphate and to some extent to chondroitin sulphate. 2. The relative binding affinities were compared by determining (a) the concentration of NaCl required to release the enzyme from polysaccharide-substituted Sepharose; (b) the concentration of free polysaccharides required to displace the enzyme from immobilized polysaccharides; and (c) the total amounts of enzyme bound after saturation of immobilized polysaccharides. By each of these criteria heparin bound the enzyme most efficiently, followed by heparan sulphate and dermatan sulphate, which were more efficient than chondroitin sulphate. 3. Heparin fractions with high and low affinity for antithrombin, respectively, did not differ with regard to affinity for lipoprotein lipase. 4. Partially N-desulphated heparin (40-50% of N-unsubstituted glucosamine residues) was unable to displace lipoprotein lipase from immobilized heparin. This ability was restored by re-N-sulphation or by N-acetylation; the N-acetylated product was essentially devoid of anticoagulant activity. 5. Partial depolymerization of heparin led to a decrease in ability to displace lipoprotein lipase from heparin-Sepharose; however, even fragments of less than decasaccharide size showed definite enzyme-releasing activity. 6. Studies with hepatic lipase (purified from rat post-heparin plasma) gave results similar to those obtained with milk lipoprotein lipase. However, the interaction between the hepatic lipase and the glycosaminoglycans was weaker and was abolished at lower concentrations of NaCl. 7. The ability of the polysaccharides to release lipoprotein lipase to the circulating blood after intravenous injection into rats essentially conformed to their affinity for the enzyme as evaluated by the experiments in vitro.

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