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Catabolism of Exogenous and Endogenous Sphingomyelin and Phosphatidylcholine by Homogenates and Subcellular Fractions of Cultured Neuroblastoma Cells. Effects of Anesthetics
Author(s) -
Mooibroek Marilyn J.,
Cook Harold W.,
Clarke Joe T. R.,
Spence Matthew W.
Publication year - 1985
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1985.tb08794.x
Subject(s) - sphingomyelin , phosphatidylcholine , biochemistry , anesthetic , endogeny , chemistry , sphingomyelin phosphodiesterase , phosphatidylethanolamine , ceramide , catabolism , diacylglycerol kinase , phospholipid , membrane , metabolism , enzyme , psychology , apoptosis , protein kinase c , psychiatry
Cultured murine neuroblastoma cells contain a neutral, Mg 2+ ‐stimulated sphingomyelinase and an alkaline phosphatidylcholine‐hydrolyzing activity that are enriched in the plasma membrane fraction. The reaction products of sphingomyelin catabolism are phosphocholine and ceramide and those of phosphatidylcholine, glycerophosphocholine and fatty acid. These reactions were studied with endogenous as well as exogenous liposomal substrates. With both exogenous and endogenous substrates, the sphingomyelinase activity was stimulated two‐to threefold by Mg 2+ and a further three‐to fourfold by volatile anesthetic agents. Stimulation was concentration‐dependent and corresponded to anesthetic potency: methoxyflurane > halothane > enflurane. Greater than 80% of the plasma membrane sphingomyelin was hydrolyzed within 2 h in the presence of Mg 2+ and anesthetic. In contrast, the activity with exogenous and endogenous phosphatidylcholine was unaffected by Mg 2+ or Ca 2+ and was markedly inhibited (50–80%) by anesthetic agents. The degree of inhibition was concentration‐dependent and corresponded to anesthetic potency. The quantitative importance of choline‐containing lipids in cell membranes, the relatively exclusive localization of the neutral Mg 2+ ‐stimulated sphingomyelinase in cells of neural origin, the totally different type of hydrolytic attack on phosphatidylcholine, and the reciprocal effects of anesthetics on the hydrolysis of these two lipids strongly suggest important roles for these activities in cell membranes in general and in the neuron in particular.