Alterations in receptor-coupled second messenger systems at up-regulated muscarinic receptors: analysis using primary cultured neurons.
The effect of a long-term exposure (5 days) to atropine on muscarinic acetylcholine receptors and receptor-coupled second messenger systems was investigated using mouse cerebral cortical neurons in primary culture. The long-term exposure of neurons to atropine (10 nM) induced increases in both the Bmax and Kd values of [3H]quinuclidinyl benzilate (QNB) binding to muscarinic acetylcholine receptors. Alterations in muscarinic receptor-coupled second messenger systems, such as phosphoinositide (PI) hydrolysis and cyclic GMP (cGMP) formation following a long-term exposure to atropine, were also examined. Carbachol-stimulated PI hydrolysis was found to be decreased by the exposure to atropine in spite of the increase of muscarinic receptors. In addition, a long-term exposure to atropine had no effect on carbachol-stimulated cGMP formation as well as on the rightward shift of the carbachol competition curve of [3H]QNB binding in the presence of GTP. These results suggest that the up-regulation in muscarinic cholinergic receptors induced by long-term exposure to atropine may involve not only the increase in number of muscarinic receptors but also the decreased responsiveness in muscarinic receptor-coupled second messenger systems.
Ohkuma
S
S
Department of Pharmacology, Kyoto Prefectural University of Medicine, Japan.
Kishi
M
M
Ma
F H
FH
Kuriyama
K
K
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002478:Cells, Cultured; D006152:Cyclic GMP / Q000096:biosynthesis; D003513:Cycloheximide / Q000494:pharmacology; D005260:Female; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006868:Hydrolysis; D007700:Kinetics; D051379:Mice; D008815:Mice, Inbred Strains; D009474:Neurons / Q000378:metabolism*; D010716:Phosphatidylinositols / Q000378:metabolism; D011247:Pregnancy; D011813:Quinuclidinyl Benzilate; D011976:Receptors, Muscarinic / Q000187:drug effects*; D015290:Second Messenger Systems / Q000502:physiology*; D015854:Up-Regulation / Q000502:physiology*
D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D011813:Quinuclidinyl Benzilate; D001285:Atropine; D006160:Guanosine Triphosphate; D002217:Carbachol; D003513:Cycloheximide; D006152:Cyclic GMP