Molecular Pharmacology, Vol 13, 242-250, Copyright © 1977 by the American Society for Pharmacology and Experimental Therapeutics

Regulation of Adenosine 3',5'-Monophosphate Content in Human Astrocytoma Cells by Isoproterenol and Carbachol

¹ Department of Biochemistry, University of Massachusetts Medical School, Worcester, Massachusetts 01605

Carbachol, a typical cholinomimetic, inhibited isoproterenol stimulation of intracellular adenosine 3',5'-monophosphate (cAMP) levels in a dose-dependent fashion, causing a maximal 60-70% decrease at 0.1 mM. The blocking action of carbachol was evident by 30 sec, and reached a maximum between 5 and 7 min. Neither lidocaine, a local anesthetic, nor ascorbic acid and thiourea, reducing agents, had any effect on the action of carbachol. Carbachol inhibited the accumulation of cAMP caused by isoproterenol, adenosine, and prostaglandin E₁. Neither hexamethonium bromide, tetraethylammonium chloride, nor phentolamine affected the regulation of cAMP levels by carbachol; in contrast, 1.0 µM atropine completely blocked its effects. Ca²⁺-free incubation medium eliminated the inhibitory effect of carbachol on isoproterenol-stimulated accumulation of cAMP, but did not affect isoproterenol stimulation alone. These observations suggest that the astrocytoma cell line has a muscarinic, Ca²⁺-dependent cholinergic receptor, the stimulation of which results in inhibition of cAMP accumulation with isoproterenol stimulation.

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ACKNOWLEDGMENTS We are most grateful for advice, help, and criticism from Dr. R. W. Butcher during the preparation of the manuscript. We would also like to thank Dr. Linda Shlatz for performing the cGMP determinations, and Natalie Seney for technical assistance.

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