Abstract
The metabolism of phosphatidate in rat parotid acinar cells was investigated, particularly with regard to the actions of agonists known to act by mobilizing Ca2+. When cells were incubated in medium containing 10 microM-[32P]Pi, phosphatidate was rapidly labelled, approaching an apparent steady-state with a half-time of approx. 20 min. Methacholine provoked a more than doubling of phosphatidate radioactivity, which was reversed by the muscarinic antagonist atropine. These results suggest that phosphatidate labels to near steady-state rapidly and that in cells prelabelled for 60 min the increase in radioactivity induced by agonists probably reflects net synthesis rather than an increase in specific radioactivity. Phosphatidate synthesis in response to methacholine was rapid and occurred, within the resolution of a few seconds, with no measurable latency. Adrenaline and substance P also stimulated phosphatidate synthesis but both agonists were less efficacious than methacholine. A Ca2+ ionophore, ionomycin, did not provoke phosphatidate synthesis. By using a protocol that eliminates the receptor-regulated Ca2+ pool, it was demonstrated that methacholine-induced phosphatidate formation does not come about as a consequence of Ca2+ influx nor of Ca2+ release. These results indicate that the phosphatidate synthesis response has characteristics compatible with its previously suggested role as a primary mediator of membrane Ca2+-gating.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- BLIGH E. G., DYER W. J. A rapid method of total lipid extraction and purification. Can J Biochem Physiol. 1959 Aug;37(8):911–917. doi: 10.1139/o59-099. [DOI] [PubMed] [Google Scholar]
- HOKIN M. R., HOKIN L. E. Effects of acetylcholine on phospholipides in the pancreas. J Biol Chem. 1954 Aug;209(2):549–558. [PubMed] [Google Scholar]
- Haddas R. A., Landis C. A., Putney J. W., Jr Relationship between calcium release and potassium release in rat parotid gland. J Physiol. 1979 Jun;291:457–465. doi: 10.1113/jphysiol.1979.sp012825. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jones L. M., Michell R. H. Cholinergically stimulated phosphatidylinositol breakdown in parotid-gland fragments is independent of the ionic environment. Biochem J. 1976 Aug 15;158(2):505–507. doi: 10.1042/bj1580505. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Jones L. M., Michell R. H. The relationship of calcium to receptor-controlled stimulation of phosphatidylinositol turnover. Effects of acetylcholine, adrenaline, calcium ions, cinchocaine and a bivalent cation ionophore on rat parotid-gland fragments. Biochem J. 1975 Jun;148(3):479–485. doi: 10.1042/bj1480479. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Kirk C. J., Creba J. A., Downes C. P., Michell R. H. Hormone-stimulated metabolism of inositol lipids and its relationship to hepatic receptor function. Biochem Soc Trans. 1981 Oct;9(5):377–379. doi: 10.1042/bst0090377. [DOI] [PubMed] [Google Scholar]
- Lapetina E. G., Cuatrecasas P. Stimulation of phosphatidic acid production in platelets precedes the formation of arachidonate and parallels the release of serotonin. Biochim Biophys Acta. 1979 May 25;573(2):394–402. doi: 10.1016/0005-2760(79)90072-9. [DOI] [PubMed] [Google Scholar]
- Lapetina E. G., Michell R. H. Stimulation by acetylcholine of phosphatidylinositol labelling. Subcellular distribution in rat cerebral-cortex slices. Biochem J. 1972 Mar;126(5):1141–1147. doi: 10.1042/bj1261141. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Michell R. H. Inositol phospholipids and cell surface receptor function. Biochim Biophys Acta. 1975 Mar 25;415(1):81–47. doi: 10.1016/0304-4157(75)90017-9. [DOI] [PubMed] [Google Scholar]
- Miller J. C., Kowal C. N. The relationship between the incorporation of 32P into phosphatidic acid and phosphatidylinositol in rat parotid acinar cells. Biochem Biophys Res Commun. 1981 Oct 15;102(3):999–1007. doi: 10.1016/0006-291x(81)91637-5. [DOI] [PubMed] [Google Scholar]
- Putney J. W., Jr Muscarinic, alpha-adrenergic and peptide receptors regulate the same calcium influx sites in the parotid gland. J Physiol. 1977 Jun;268(1):139–149. doi: 10.1113/jphysiol.1977.sp011851. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Putney J. W., Jr, Poggioli J., Weiss S. J. Receptor regulation of calcium release and calcium permeability in parotid gland cells. Philos Trans R Soc Lond B Biol Sci. 1981 Dec 18;296(1080):37–45. doi: 10.1098/rstb.1981.0169. [DOI] [PubMed] [Google Scholar]
- Putney J. W., Jr, VanDeWalle C. M., Leslie B. A. Receptor control of calcium influx in parotid acinar cells. Mol Pharmacol. 1978 Nov;14(6):1046–1053. [PubMed] [Google Scholar]
- Putney J. W., Jr, Weiss S. J., Van De Walle C. M., Haddas R. A. Is phosphatidic acid a calcium ionophore under neurohumoral control? Nature. 1980 Mar 27;284(5754):345–347. doi: 10.1038/284345a0. [DOI] [PubMed] [Google Scholar]
- Roberts M. L., Petersen O. H. Membrane potential and resistance changes induced in salivary gland acinar cells by microiontophoretic application of acetylcholine and adrenergic agonists. J Membr Biol. 1978 Mar 20;39(4):297–312. doi: 10.1007/BF01869896. [DOI] [PubMed] [Google Scholar]
- Salmon D. M., Honeyman T. W. Proposed mechanism of cholinergic action in smooth muscle. Nature. 1980 Mar 27;284(5754):344–345. doi: 10.1038/284344a0. [DOI] [PubMed] [Google Scholar]
- Weiss S. J., Putney J. W., Jr The relationship of phosphatidylinositol turnover to receptors and calcium-ion channels in rat parotid acinar cells. Biochem J. 1981 Feb 15;194(2):463–468. doi: 10.1042/bj1940463. [DOI] [PMC free article] [PubMed] [Google Scholar]