Muscarinic-stimulated norepinephrine release and phosphoinositide hydrolysis in PC12 cells are independent events.
This laboratory has reported recently that muscarinic receptor-stimulated release of norepinephrine from pheochromocytoma (PC12) cells is dependent upon an influx of Ca2+ through a Ca2+ channel that is regulated by a pertussis toxin-sensitive GTP-binding protein (G-protein) (Inoue, K., and Kenimer J. G. (1988) J. Biol. Chem. 263, 8157-8161). In the present study, we have examined the role of phosphoinositide hydrolysis in this mechanism. The muscarinic agonist methacholine was shown to stimulate phosphoinositide hydrolysis by a mechanism that was sensitive to pertussis toxin inhibition. When assayed in the absence of Ca2+, muscarinic-stimulated norepinephrine release but not phosphoinositide hydrolysis was blocked. Conversely, muscarinic-stimulated phosphoinositide hydrolysis but not norepinephrine release was blocked in cells preincubated with phorbol 12,13-dibutyrate. In contrast to several previous hypotheses that suggested that muscarinic-stimulated neurotransmitter release is dependent upon phosphoinositide hydrolysis, our results suggest that these two muscarinic-stimulated processes are independent events in PC12 cells. Inhibition studies with muscarinic receptor subtype-specific antagonists suggest that norepinephrine release is regulated by an M2 subtype muscarinic receptor and that phosphoinositide hydrolysis is regulated by an M3 subtype muscarinic receptor.
Takashima
A
A
Center for Biologics Evaluation and Research, Food and Drug Administration, Bethesda, Maryland 20892.
Kenimer
J G
JG
D000310:Adrenal Gland Neoplasms; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002460:Cell Line; D003959:Diamines / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D016210:Methacholine Chloride; D008688:Methacholine Compounds / Q000494:pharmacology*; D009638:Norepinephrine / Q000378:metabolism*; D010277:Parasympathomimetics / Q000494:pharmacology*; D010673:Pheochromocytoma; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D010890:Pirenzepine / Q000494:pharmacology; D051381:Rats; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*
D003959:Diamines; D008688:Methacholine Compounds; D010277:Parasympathomimetics; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D016210:Methacholine Chloride; D015240:Phorbol 12,13-Dibutyrate; D010890:Pirenzepine; D001285:Atropine; C054938:methoctramine; D009638:Norepinephrine