Methylamine does not inhibit rates of endogenous lipolysis in isolated myocardial cells from rat heart

1987 ◽  
Vol 65 (2) ◽  
pp. 226-229 ◽  
Author(s):  
Albert Kryski Jr. ◽  
Terje S. Larsen ◽  
Ignasi Ramírez ◽  
David L. Severson
Keyword(s):  
Fatty Acids ◽  
Lipase Activity ◽  
Rat Heart ◽  
Diabetic Rat ◽  
Myocardial Cells ◽  
Acid Lipase ◽  
Ph Optimum ◽  
Triacylglycerol Lipase ◽  
Rat Hearts ◽  
Lysosomotropic Agent

Triacylglycerol lipase activity with a pH optimum of 5 was present in homogenates of myocardial cells from rat heart. Acid lipase activity was inhibited by serum, heparin, and increased ionic strength. Methylamine, a lysosomotropic agent, did not inhibit the basal or isoproterenol-stimulated rate of endogenous lipolysis as measured by glycerol output from control myocytes. Similarly, accelerated rates of glycerol output that are a consequence of an elevation in the intracellular stores of triacylglycerols in myocytes from diabetic rat hearts and from myocytes prepared with free fatty acids in the isolation solutions were not reduced by methylamine. Therefore, the acid lysosomal triacylglycerol lipase must not be involved in the mobilization of endogenous triacylglycerols in myocardial cells from rat heart.

scholarly journals Triacylglycerol Lipase Activities of Cultured Rat L6 Myoblasts

1985 ◽  
Vol 38 (1) ◽  
pp. 41
Author(s):  
RK Tume ◽  
F D Shaw
Keyword(s):  
Lipoprotein Lipase ◽  
Cell Lines ◽  
Lipase Activity ◽  
Maximum Velocity ◽  
Acid Lipase ◽  
Ph Optimum ◽  
Triacylglycerol Lipase ◽  
Inhibitory Component ◽  
Cell Homogenate ◽  
Hydrolysis Of

The utilization of exogenous triacylglycerol by fusing and non-fusing rat L6 myoblasts grown in culture was investigated. Although small quantities of triacylglycerol were accumulated by both cell lines during an incubation of 2 h, no evidence could be found for the presence of lipoprotein lipase, either in the cells or released into the medium. Cell homogenate studies confirmed the absence of lipoprotein lipase but revealed the presence of an acid lipase having a pH optimum at 4�6. Acid lipase activity was mainly associated with a 15 000 g pellet and was capable of hydrolysing triolein at maximum velocity in the millimolar range. Unlike lipoprotein lipase, acid lipase was strongly inhibited by serum and preliminary investigations suggest that the inhibitory component of serum is located amongst the higher density lipoproteins. It is likely that the acid lipase is of lysosomal origin and is responsible for the hydrolysis of internalized triacylglycerol for subsequent utilization by the cell.

Lipolysis in isolated myocardial cells from diabetic rat hearts

1985 ◽  
Vol 249 (5) ◽  
pp. H1024-H1030 ◽  
Author(s):  
K. A. Kenno ◽  
D. L. Severson
Keyword(s):  
Fatty Acids ◽  
Free Fatty Acids ◽  
Diabetic Rat ◽  
Myocardial Cells ◽  
Atp Content ◽  
Intracellular Accumulation ◽  
Rat Hearts ◽  
Triacylglycerol Content ◽  
Release Of Glycerol ◽  
Stimulation Of

Diabetes in rats was induced with streptozotocin (100 mg/kg); myocardial cells (myocytes) were isolated from the hearts 3-4 days later. Diabetic myocytes were characterized as having the same viability and ATP content as control myocytes, but the yield was reduced. The triacylglycerol content of diabetic myocytes was elevated by 3.7-fold; this resulted in an increased rate of glycerol output during subsequent incubations. There was a stoichiometric relationship between the decline in the cellular triacylglycerol content and the release of glycerol into the incubation medium. Isoproterenol stimulated the output of glycerol from control myocytes by about twofold, but the stimulation of glycerol output from diabetic myocytes by isoproterenol was markedly less. The combination of 1-methyl-3-isobutylxanthine with isoproterenol or 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate also failed to produce the same lipolytic response in diabetic myocytes as in control myocytes. Triacylglycerol-loaded myocytes from control rats, prepared by including palmitate in the isolation buffers, were also characterized as having increased basal rates of glycerol output and a reduced lipolytic response to isoproterenol. The level of free fatty acids in diabetic myocytes was 2.8-fold greater than in myocytes from control hearts. The intracellular accumulation of free fatty acids in these quiescent populations of diabetic myocytes may limit the ability of catecholamines to produce a further stimulation of lipolysis.

Regulation of lysophosphatidylcholine-metabolizing enzymes in isolated myocardial cells from rat heart

1985 ◽  
Vol 63 (8) ◽  
pp. 944-951 ◽  
Author(s):  
David L. Severson ◽  
Thea Fletcher
Keyword(s):  
Fatty Acids ◽  
Palmitic Acid ◽  
Free Fatty Acids ◽  
Rat Heart ◽  
Marked Reduction ◽  
Myocardial Cells ◽  
Acyltransferase Activity ◽  
Metabolizing Enzymes ◽  
Enzymatic Pathways ◽  
Lysophospholipase Activity

Enzymatic pathways involved in the metabolism of lysophosphatidylcholine were investigated in rat heart myocardial cells. Acyl CoA-dependent acyltransferase activity was localized in microsomes, and was much greater than lysophospholipase activity in either cytosolic or microsomal fractions. The cytosolic lysophospholipase was more sensitive to inhibition by palmitylcarnitine in comparison to free fatty acids. In contrast, free fatty acids (oleate and palmitate) produced a greater inhibition of the microsomal acyltransferase and lysophospholipase than did palmitylcarnitine. A reduction in the assay pH to 6.5 resulted in an increase in microsomal acyltransferase and cytosolic lysophospholipase activities, but brought about a marked reduction in the microsomal lysophospholipase activity. At pH 6.5, the percentage inhibition of the microsomal acyltransferase by palmitylcarnitine was reduced, whereas the inhibition by palmitic acid was enhanced. The inhibition of the microsomal lysophospholipase by both palmitylcarnitine and palmitic acid was reduced at pH 6.5. With respect to myocardial ischemia, the inhibition of microsomal acyltransferase by free fatty acids and the reduction in microsomal lysophospholipase activity due to acidosis may contribute to the elevation of cellular lysophosphoglycerides which are arrhythmogenic.

Metabolic fate of rat heart endothelial lipoprotein lipase

1988 ◽  
Vol 255 (3) ◽  
pp. E247-E254 ◽  
Author(s):  
T. Chajek-Shaul ◽  
G. Bengtsson-Olivecrona ◽  
J. Peterson ◽  
T. Olivecrona
Keyword(s):  
Lipoprotein Lipase ◽  
Lipase Activity ◽  
Rat Heart ◽  
Metabolic Fate ◽  
Low Concentrations ◽  
Rat Hearts ◽  
Catalytically Active ◽  
Isolated Rat

When isolated rat hearts were perfused with medium containing 125I-labeled bovine lipoprotein lipase (LPL), they bound both lipase activity and radioactivity. More than 80% of the bound lipase could be rapidly released by heparin. Low concentrations of bovine LPL displaced 50-60% of the endogeneous, endothelial-bound LPL. Higher concentrations caused additional binding. Both binding and exchange were rapid processes. The hearts continuously released endogenous LPL into the medium. An antiserum that inhibited bovine but not rat LPL was used to differentiate endogeneous and exogeneous LPL activity. When the pool of endothelial LPL was labeled with bovine 125I-labeled LPL and then chased with unlabeled bovine LPL, approximately 50% of the labeled lipase was rapidly displaced. During chase perfusion with medium only, catalytically active bovine LPL appeared in the perfusate. The rate of release was similar to that observed for endogeneous LPL activity and amounted to 10-13% of the heparin-releasable fraction in the first 5 min of perfusion. There was little or no degradation of bovine 125I-labeled LPL to fragments or acid-soluble products. These results indicate that endothelial LPL is accessible for exchange with exogeneous LPL and that detachment rather than degradation may be the pathway for catabolism of endothelial LPL.

Reduced high-energy phosphate levels in rat hearts. I. Effects of alloxan diabetes

1976 ◽  
Vol 230 (6) ◽  
pp. 1744-1750 ◽  
Author(s):  
TB Allison ◽  
SP Bruttig ◽  
Crass MF ◽  
RS Eliot ◽  
JC Shipp
Keyword(s):  
Oxidative Metabolism ◽  
Oxygen Delivery ◽  
Rat Heart ◽  
High Energy ◽  
Diabetic Rat ◽  
High Energy Phosphate ◽  
Atp Production ◽  
Rat Hearts

Significant alterations in heart carbohydrate and lipid metabolism are present 48 h after intravenous injection of alloxan (60 mg/kg) in rats. It has been suggested that uncoupling of oxidative phosphorylation occurs in the alloxanized rat heart in vivo, whereas normal oxidative metabolism has been demonstrated in alloxan-diabetic rat hearts perfused in vitro under conditions of adequate oxygen delivery. We examined the hypothesis that high-energy phosphate metabolism might be adversely affected in the alloxan-diabetic rat heart in vivo. Phosphocreatine and ATP were reduced by 58 and 45%, respectively (P is less than 0.001). Also, oxygen-dissociation curves were shifted to the left by 4 mmHg, and the rate of oxygen release from blood was reduced by 21% (P is less than 0.01). Insulin administration normalized heart high-energy phosphate compounds. ATP production was accelerated in diabetic hearts perfused in vitro with a well-oxygenated buffer. These studies support the hypothesis that oxidative ATP production in the alloxan-diabetic rat heart is reduced and suggest that decreased oxygen delivery may have a regulatory role in the oxidative metabolism of the diabetic rat heart.

scholarly journals Decrease in cardiac phosphatidylglycerol in streptozotocin-induced diabetic rats does not affect cardiolipin biosynthesis: evidence for distinct pools of phosphatidylglycerol in the heart

1995 ◽  
Vol 306 (3) ◽  
pp. 759-764 ◽  
Author(s):  
G M Hatch ◽  
S G Cao ◽  
A Angel
Keyword(s):  
Rat Heart ◽  
Specific Radioactivity ◽  
Fold Increase ◽  
Mitochondrial Fraction ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Rat Hearts ◽  
Perfused Hearts ◽  
Continuous Pulse ◽  
Pool Sizes

Biosynthesis of phosphatidylglycerol (PG) and cardiolipin (CL) were investigated in perfused hearts of diabetic rats 4 days or 28 days after streptozotocin injection. Sham-injected and insulin-treated diabetic rats were used as controls. In addition, another group of rats fasted for 54 h was examined. Isolated rat hearts from these groups were perfused for 30 min with [32P]P(i), and the radioactivity incorporated into PG and CL and their pool sizes were determined in heart ventricles. There was no difference in the amount of radioactivity incorporated into CL, PG or other phospholipids between all groups. In addition, the pool sizes of CL and other phospholipids were unaltered. However, a striking decrease in the pool size of PG was observed in both diabetic and fasted rats compared to sham- and insulin-treated controls at 4 days after streptozotocin injection. The decrease in PG mass in diabetic rats was rapid (within 24-48 h) and was localized to cardiac membranes. Diabetes did not affect the activity of the enzymes of PG and CL biosynthesis in the mitochondrial fraction, or phospholipase A activity in subcellular fractions prepared from rat heart homogenates. In addition, pulse-chase experiments confirmed that diabetes did not affect the rate of new PG or CL biosynthesis. Since radioactivity associated with PG was unaltered in continuous-pulse perfusion experiments, a calculated 1.8-fold increase in the specific radioactivity of cardiac PG was observed in the hearts of acute diabetic rats compared with controls. Since the radioactivity incorporated into PG and CL, and the rate of CL biosynthesis, were unaltered in diabetic-rat hearts compared with controls, new CL was probably synthesized from newly synthesized PG. We postulate the existence of distinct pools of PG in the heart, and that the pool of newly synthesized PG used for CL biosynthesis does not appear to mix immediately with the pre-existing pool of PG in the isolated intact rat heart.

Effect of experimental diabetes on isolated rat heart responsiveness to isoproterenol

1984 ◽  
Vol 62 (1) ◽  
pp. 124-131 ◽  
Author(s):  
Rao V. S. V. Vadlamudi ◽  
John H. McNeill
Keyword(s):  
Rat Heart ◽  
Experimental Diabetes ◽  
Isolated Rat Heart ◽  
Energy Utilization ◽  
Diabetic Rat ◽  
Noradrenaline Content ◽  
Relaxant Effect ◽  
Rat Hearts ◽  
Relaxing Effect ◽  
Working Rat Heart

The isolated perfused working rat heart was used to study experimental diabetes-induced alterations in the sensitivity and responsiveness of the myocardium to the effects of isoproterenol. Experimental diabetes was induced by intravenous administration of either 65 mg/kg alloxan or 60 mg/kg streptozotocin. The positive inotropic and cardiac relaxant effects of isoproterenol were studied at various time points after the induction of diabetes. There were no changes either in the sensitivity or in the maximum responses of diabetic rat hearts to the positive inotropic effect of isoproterenol at any time point studied. However, the cardiac relaxant effect of isoproterenol was depressed in acute as well as chronic diabetic rat hearts when compared with age-matched controls. Ventricular noradrenaline content was unchanged in 180-day diabetic rat hearts indicating the absence of a diabetes-induced sympathetic neuropathy in the heart. The depressed relaxing effect of isoproterenol may have resulted from alterations in energy utilization and sarcoplasmic reticular function in diabetic rat hearts.

Effects of high levels of fatty acids on functional recovery of ischemic hearts from diabetic rats

1992 ◽  
Vol 263 (6) ◽  
pp. E1046-E1053 ◽  
Author(s):  
G. D. Lopaschuk ◽  
M. Saddik ◽  
R. Barr ◽  
L. Huang ◽  
C. C. Barker ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Functional Recovery ◽  
Recovery Of Function ◽  
Heart Function ◽  
Diabetic Rats ◽  
Diabetic Rat ◽  
Mechanical Function ◽  
Rat Hearts ◽  
Reperfusion Period ◽  
High Concentrations

In this study we determined the effects of high levels of fatty acids on recovery of heart function when present either during or after ischemia. Isolated working hearts from 6-wk streptozotocin diabetic and control rats perfused with 11 mM glucose were subjected to 25 min of global ischemia followed by 30 min of aerobic reperfusion. Four groups were studied: 1) 1.2 mM palmitate present before, during, and after ischemia; 2) 1.2 mM palmitate present before and during ischemia, followed by reperfusion in the absence of palmitate; 3) no palmitate before and during ischemia, followed by 1.2 mM palmitate during reperfusion; and 4) no palmitate before and during ischemia or during reperfusion. In control hearts, palmitate during reperfusion depressed recovery of function regardless of whether palmitate was present or absent during ischemia. In contrast, palmitate present during reperfusion did not depress recovery of mechanical function in the diabetic rat hearts. However, the presence of palmitate during ischemia itself in diabetic rat hearts was detrimental to recovery of mechanical function. The presence of palmitate during ischemia resulted in an accelerated rate of ATP loss and a decreased rate of lactate accumulation during ischemia, although this effect was similar in control and diabetic rat hearts. Our results demonstrate that high concentrations of fatty acids depress functional recovery of control rat hearts during the reperfusion period but depress recovery of function in diabetic rat hearts when present during ischemia itself.

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