Cyclic AMP potentiates receptor-stimulated phosphoinositide hydrolysis in human neuroepithelioma cells.
A stimulatory role for cAMP in the regulation of receptor-activated phosphoinositide hydrolysis has been examined in human SK-N-MCIXC and SK-N-MCIIE neuroepithelioma cells. The addition of optimal concentrations of oxotremorine-M, norepinephrine, endothelin-1, and ATP enhanced the release of inositol phosphates by 2-9-fold after activation of muscarinic, alpha 1-adrenergic, endothelin, and P2 nucleotide receptors, respectively. All combinations of these agonists elicited a release of inositol phosphates that was at least additive. However, the combined presence of oxotremorine-M and norepinephrine resulted in a phosphoinositide hydrolysis that was 30% greater than additive. This potentiation of inositol lipid hydrolysis resulted from an increased activity of the muscarinic receptor after the addition or norepinephrine and persisted after alpha 1-adrenergic receptor blockade. The enhancement of muscarinic receptor-stimulated inositol phosphate release could be quantitatively mimicked by inclusion of the beta-adrenergic agonist isoproterenol (EC50 approximately 0.1 microM), but not by alpha 1- or alpha 2-adrenergic agonists. Potentiation of oxotremorine-M-stimulated inositol lipid hydrolysis observed in the presence of either norepinephrine or isoproterenol was reduced in the absence of added Ca2+. Addition of either norepinephrine or isoproterenol to SK-N-MCIXC cells also resulted in a 16-fold increase in cAMP concentration. Although the cell-permeant 8-chloro-4-phenylthio-cAMP had a small inhibitory effect on basal inositol phosphate release, its inclusion resulted in a 19-31% enhancement of muscarinic, endothelin, ATP, and alpha 1-adrenergic receptor-stimulated phosphoinositide hydrolysis. We conclude 1) that, in SK-N-MCIXC cells, the addition of beta-adrenergic agonists selectively enhances muscarinic receptor-stimulated phosphoinositide hydrolysis through a cAMP-dependent process and 2) that the ability of exogenously added cAMP to enhance the activation of all four inositol lipid-linked receptors indicates that the effects of cAMP on inositol lipid hydrolysis are compartmentalized in these cells.
Neuroscience Laboratory, University of Michigan, Ann Arbor 48104.
S K
SK
Fisher
E L
EL
McEwen
S C
SC
Lovell
R E
RE
Landon
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology* / Q000502:physiology; D004357:Drug Synergism; D016232:Endothelins / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D007295:Inositol Phosphates / Q000096:biosynthesis; D018241:Neuroectodermal Tumors, Primitive, Peripheral / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010095:Oxotremorine / Q000031:analogs & derivatives / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011942:Receptors, Adrenergic, alpha / Q000502:physiology; D011976:Receptors, Muscarinic / Q000502:physiology; D011983:Receptors, Purinergic / Q000502:physiology; D013268:Stimulation, Chemical; D014407:Tumor Cells, Cultured
D000318:Adrenergic beta-Agonists; D016232:Endothelins; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D011942:Receptors, Adrenergic, alpha; D011976:Receptors, Muscarinic; D011983:Receptors, Purinergic; D010095:Oxotremorine; C042743:oxotremorine M; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D009638:Norepinephrine