Abnormal synthesis of N-methylated phospholipids during calcium paradox of the heart.
Phosphatidylethanolamine (PtdEtn) N-methyltransferase activity that synthesizes phosphatidylcholine (PtdCho) via formation of methylated intermediates (phosphatidyl-N-monomethylethanolamine, PtdEtnMe and phosphatidyl-N,N-dimethylethanolamine, PtdEtnMe2) was comparatively studied in rat heart sarcolemmal (SL), sarcoplasmic reticular (SR) and mitochondrial fractions during Ca2+ paradox. Perfusion (5 min) with Ca(2+)-free medium followed by reperfusion (5 min) with Ca(2+)-containing medium produced a marked rise in resting tension without any recovery of contractile force. Methyltransferase catalytic sites I, II and III which synthesize PtdEtnMe, PtdEtnMe2 and PtdCho, respectively, were assayed by measuring the [3H] methyl group incorporation from 0.055, 10 and 150 microM S-adenosyl-L-[3H-methyl] methionine into membrane PtdEtn molecules. Five minutes of perfusion with Ca(2+)-free medium did not affect either SL or SR N-methyltransferase systems. Ca(2+)-readmission for 1 to 5 min induced a selective, time-dependent depression of SL site II and SR site I methyltransferase activities. Individual N-methylated phospholipids specifically formed at the two sites reflected these changes. The above abnormalities were differently influenced by the duration (1-5 min) of Ca(2+)-free perfusion and were characterized by different kinetic alterations. The mitochondrial methylation system was not affected under Ca2+ paradox. The results suggest that reduced synthesis of SL N-methylated phospholipids may contribute to the contractile dysfunction observed in Ca2+ paradox.
Persad
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Division of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada.
Panagia
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D000818:Animals; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology*; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D008745:Methylation; D008780:Methyltransferases / Q000378:metabolism*; D008929:Mitochondria, Heart / Q000378:metabolism; D009200:Myocardial Contraction / Q000187:drug effects; D009206:Myocardium / Q000378:metabolism*; D010477:Perfusion; D010713:Phosphatidylcholines / Q000378:metabolism*; D050918:Phosphatidylethanolamine N-Methyltransferase; D010714:Phosphatidylethanolamines / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012436:S-Adenosylmethionine / Q000378:metabolism; D012508:Sarcolemma / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D012436:S-Adenosylmethionine; D008780:Methyltransferases; D050918:Phosphatidylethanolamine N-Methyltransferase; D002118:Calcium