Myocardial ischemia is accompanied by accelerated phospholipid catabolism resulting in the depletion of membrane phospholipids and the accumulation of amphiphilic metabolites which alter electrophysiologic function and predispose to ventricular dysrhythmia. Alterations in myocyte ionic permeability and electrophysiologic function are most likely mediated by changes in the chemical composition of the sarcolemmal membrane. Recently we have identified plasmalogen as the major phospholipid constituent of canine myocardial sarcolemma. Since catabolism of sarcolemmal phospholipids likely contributes to ventricular dysrhythmia and ischemic membrane dysfunction and since the catabolic pathways of plasmalogens in myocardium have not been identified, we developed a convergent synthesis for the preparation of homogeneous radiolabeled choline and ethanolamine plasmalogens and have identified two novel mammalian phospholipase activities in canine myocardium which hydrolyze plasmalogen. A neutral active calcium-independent phospholipase A2 which is selective for the hydrolysis of the sn-2 fatty acid of plasmalogens and a neutral active phospholipase C specific for choline and ethanolamine glycerophospholipid have been identified. Flux through these catabolic pathways results in the production of several biologically important lipids including arachidonic acid, lysoplasmalogen, and diglycerides. The objective of the proposed research is the purification and characterization of myocardial phospholipases A2 and C and the identification of the regulatory mechanisms which modulate the enzymic activity of these phospholipases in myocardium. We will purify myocardial neutral active phospholipase C activity which hydrolyzes choline and ethanolamine glycerophospholipids, identify fhte chemical nature of an endogenous inhibitor of enzymic activity present in the cytosol and determine factors which modify the inhibitor-enzyme interaction and therefore likely modulate enzymic activity. Next we will purify myocardial plasmalogen-selective phospholipase A2 activity and characterize the mechanism of its modulation by cAMP. FInally we will identify, characterize and purify sarcolemmal enzymes which catalyze the catabolism of plamsalogens and characterize their modulation by ligant-receptor coupling. Taken together the proposed research will delineate the catabolic pathways of plasmalogens in myocardium and identify modulators of enzymic activity which regulate the production of several biologically active metabolites which likely contribute to the sequelae of myocardial ischemia.

Agency
National Institute of Health (NIH)
Institute
National Heart, Lung, and Blood Institute (NHLBI)
Type
Research Project (R01)
Project #
5R01HL034839-05
Application #
3348253
Study Section
Physiological Chemistry Study Section (PC)
Project Start
1985-09-30
Project End
1991-03-31
Budget Start
1989-09-30
Budget End
1991-03-31
Support Year
5
Fiscal Year
1989
Total Cost
Indirect Cost
Name
Washington University
Department
Type
Schools of Medicine
DUNS #
062761671
City
Saint Louis
State
MO
Country
United States
Zip Code
63130
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Turk, J; Gross, R W; Ramanadham, S (1993) Amplification of insulin secretion by lipid messengers. Diabetes 42:367-74
Gross, R W; Ramanadham, S; Kruszka, K K et al. (1993) Rat and human pancreatic islet cells contain a calcium ion independent phospholipase A2 activity selective for hydrolysis of arachidonate which is stimulated by adenosine triphosphate and is specifically localized to islet beta-cells. Biochemistry 32:327-36
Ramanadham, S; Gross, R W; Han, X et al. (1993) Inhibition of arachidonate release by secretagogue-stimulated pancreatic islets suppresses both insulin secretion and the rise in beta-cell cytosolic calcium ion concentration. Biochemistry 32:337-46
Ramanadham, S; Bohrer, A; Gross, R W et al. (1993) Mass spectrometric characterization of arachidonate-containing plasmalogens in human pancreatic islets and in rat islet beta-cells and subcellular membranes. Biochemistry 32:13499-509
Ford, D A; Gross, R W (1992) Metabolism of ether-linked diglycerides in brain and myocardium. Methods Enzymol 209:413-23

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