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Carbachol and Bradykinin Increase the Production of Diacylglycerol from Sources Other than Inositol‐Containing Phospholipids in PC12 Cells
Author(s) -
Horwitz Joel
Publication year - 1990
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.1471-4159.1990.tb02347.x
Subject(s) - diacylglycerol kinase , carbachol , inositol , phosphatidylinositol , diglyceride , bradykinin , chemistry , phospholipase c , endocrinology , medicine , phospholipid , biochemistry , biology , protein kinase c , stimulation , receptor , signal transduction , enzyme , membrane
Both carbachol and bradykinin increased diacylglycerol formation in PC12 pheochromocytoma cells. The effect of carbachol was apparent only in cells that had been treated with nerve growth factor. Incubation of the cells in Ca 2+ ‐free medium attenuated carbachol‐stimulated diacylglycerol formation but did not reduce the response to bradykinin. Pretreatment of the cells with pertussis toxin did not affect either carbachol‐ or bradykinin‐stimulated diacylglycerol formation; therefore, the inhibitory guanine nucleotide G i probably does not mediate this response. The time course of carbachol‐stimulated diacylglycerol accumulation did not coincide with the time course of inositol 1,4,5‐trisphosphate (IP 3 ) production. IP 3 was elevated at the earliest time measured, 15 s, and then slowly declined so that by 5 min IP 3 levels were only 50% of maximal. Diacylglycerol levels, in contrast, were not elevated for the first 2 min and then peaked at 5 min. These data indicate that hydrolysis of phosphatidylinositol 4,5‐bisphosphate was not the major source of the diacylglycerol peak at 5 min. To investigate the source of diacylglycerol, I examined the fatty acid composition of the diacylglycerol by prelabeling the cells with [ 3 H]palmitic acid and [ 14 C]stearic acid. The 14 C/ 3 H ratio in diacylglycerol should reflect the phospholipid(s) from which it is derived. The 14 C/ 3 H ratio of the increment in diacylglycerol produced by carbachol and bradykinin was intermediate between the 14 C/ 3 H ratios of phosphatidylcholine and phosphatidylinositol. The 14 C/ 3 H ratio in triacylglycerol was similar to that of phosphatidylcholine. These data indicate that carbachol and bradykinin stimulate the formation of diacylglycerol from sources other than inositol‐containing phospholipids; phosphatidylcholine and triacylglycerol are two possible sources of this diacylglycerol.