Identification of multiple phosphoinositide-linked receptors on human SK-N-MC neuroepithelioma cells.
The biochemical and pharmacological characteristics of receptor-stimulated phosphoinositide (PPI) hydrolysis in human SK-N-MC neuroepithelioma cells have been examined. Of 11 ligands tested, the addition of four, i.e., norepinephrine, oxotremorine-M, endothelin-1, and ATP, each resulted in an increased release (three- to eightfold) of inositol phosphates from [3H]inositol-prelabeled cells. Agonist-stimulated PPI turnover was sustained for at least 30 min and required the addition of Ca2+ for full effect. An increased release of inositol phosphates could also be elicited by the addition of the Ca2+ ionophore, ionomycin. All four agonists enhanced the release of radiolabeled inositol mono- and bisphosphates, inositol 1,3,4-trisphosphate, and inositol tetrakisphosphate. Increases in inositol 1,4,5-trisphosphate were smaller and only consistently observed in the presence of norepinephrine or oxotremorine-M. Norepinephrine-stimulated PPI turnover was potently inhibited by prazosin, WB-4101, and 5-methylurapidil (Ki less than 2.5 nM), but was relatively insensitive to chlorethylclonidine pretreatment. This pharmacological profile is consistent with the involvement of an alpha 1A-receptor subtype. The presence of an M1 muscarinic cholinergic receptor is also indicated, because pirenzepine blocked oxotremorine-M-stimulated inositol phosphate release (Ki = 35 nM) with a 30-fold greater potency than the M2-selective antagonist, AF-DX 116. Of the three endothelins tested, only the addition of endothelin-1 and endothelin-2 promoted PPI hydrolysis, whereas endothelin-3 was essentially inactive. A P2 nucleotide receptor of broad agonist specificity is also present on these cells and activates PPI turnover in the absence of a generalized increase in plasma membrane permeability. These results indicate that SK-N-MC cells express at least four PPI-linked receptors. Because the functional coupling of three of these receptors, i.e., alpha 1A-adrenergic, endothelin, and P2 nucleotide, has not been extensively characterized previously in neural tissues, the SK-N-MC cell line may provide a useful model system for studies of these receptors and their regulation.
Fisher
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SK
Neuroscience Laboratory, University of Michigan, Ann Arbor 48104-1687.
Landon
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RE
D000322:Adrenergic Agonists / Q000494:pharmacology; D002460:Cell Line; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D018241:Neuroectodermal Tumors, Primitive, Peripheral / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism*; D011685:Purine Nucleotides / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011976:Receptors, Muscarinic / Q000378:metabolism; D011983:Receptors, Purinergic / Q000378:metabolism
D000322:Adrenergic Agonists; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011685:Purine Nucleotides; D011941:Receptors, Adrenergic; D011956:Receptors, Cell Surface; D011976:Receptors, Muscarinic; D011983:Receptors, Purinergic