α2‐Adrenergic and Muscarinic Cholinergic Receptors Have Oposing Actions on Cyclic AMP Levels in SK‐N‐SH Human Neuroblastoma Cells
- 1 August 1989
- journal article
- research article
- Published by Wiley in Journal of Neurochemistry
- Vol. 53 (2), 602-609
- https://doi.org/10.1111/j.1471-4159.1989.tb07376.x
Abstract
Forskolin and vasoactive intestinal polypeptide (VIP) were shown to increase cyclic AMP accumulation in a human neuroblastoma cell line, SK-N-SH cells. The .alpha.2-adrenergic agonist UK 14304 decreased forskolin-stimulated cyclic AMP levels by 40 .+-. 2%, with an EC50 of 83 .+-. 20 nM. This response was blocked by pretreatment with pertussis toxin (PT) (EC50 = 1 ng/ml) or by the .alpha.2-antagonists yohimbine, idazoxan, and phentolamine. Antagonist IC50 values were 0.3 .+-. 0.1, 2.2 .+-. 0.3, and 1.4 .+-. 0.1 .mu.M, respectively. This finding suggests the presence of normal inhibitory coupling of SK-N-SH cell .alpha.2-adrenergic receptors to adenylate cyclase via the inhibitory GTP-binding protein species, Gi. Muscarinic receptors in many target cell types are coupled to inhibition of adenylate cyclase. However, in SK-N-SH cells, msucarinic agonists synergistically increased (67-95%) the level of cyclic AMP accumulation elicited by forskolin or VIP. EC50 values for carbamylcholine (CCh) and oxotremorine facilitation of the forskolin response were 1.2 .+-. 0.2 and 0.3 .+-. 0.1 .mu.M, respectively. Pharmacological studies using the muscarinic receptor subtype-preferring antagonists 4-diphenylacetoxy-N-methylpiperidine, pirenzepine, and AF-DX 116 indicated mediation of this response by the M3 subtype. IC50 values were 14 .+-. 1, 16,857 .+-. 757, and 148,043 .+-. 16,209 nM, respectively. CCh-elicited responses were unaffected by PT pretreatment. Muscarinic agonist binding affinity was indirectly measured by the ability of CCh to compete for [3H]quinuclidinyl benzilate binding sites on SK-N-SH cell membranes. Our results indicated the presence of a single CCh binding site with an apparent affinity (Ki = 5 .+-. 1 .mu.M) consistent with that concentration of agonist required to evoke biochemical responses in the intact cell.Keywords
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