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AJP - Cell Physiology, Vol 265, Issue 4 C927-C933, Copyright © 1993 by American Physiological Society
ARTICLES |
M. Chuang, M. W. Lee, D. Zhao and D. L. Severson
Medical Research Council Signal Transduction Group, Faculty of Medicine, University of Calgary, Alberta, Canada.
The regulatory effects of diacylglycerol (DAG) second messengers will be terminated by metabolism. A long-chain DAG, 1-palmitoyl-2-[1-14C]oleoyl-sn-glycerol (2-[14C]POG), was metabolized by cultured A10 smooth muscle cells after permeabilization by preincubation with 340 U/ml alpha-toxin from Staphylococcus aureus. In contrast to results with the cell-permeable DAG analogue, dioctanoyl-glycerol ([3H]diC8), no appreciable 2-[14C]POG degradation could be detected in control A10 cells not treated with alpha-toxin. With permeabilized A10 cells, 2-[14C]POG was mainly converted into lipolytic products of a lipase pathway, monoacylglycerol (MG) and fatty acid (FA); very little radioactivity was incorporated into triacylglycerol (TG) or phospholipid (PL) via reactions catalyzed by either DAG acyltransferase, cholinephosphotransferase, or DAG kinase. Similar results were obtained in experiments with 1-stearoyl-2-[1-14C]arachidonoyl-sn-glycerol. The conversion of 2-[14C]POG into PL and TG was not enhanced by the addition of 1 mM ATP-MgCl2, 1 mM CDP-choline, or 1 mM oleoyl-CoA to the alpha-toxin-treated A10 cells. The formation of FA and MG by permeabilized A10 cells was inhibited by DAG lipase inhibitors, U-57,908 (50 microM) and tetrahydrolipstatin (1-25 nM). The predominant contribution of the lipase pathway to the metabolism of a long-chain DAG, 2-[14C]POG, by alpha-toxin-treated A10 cells is similar to results for the degradation of [3H]diC8 by intact A10 cells.
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