Differences in ligand binding and phosphoinositide turnover between M1 muscarinic receptor gene transfected cells and mouse and rat brain membranes.
The present study describes some unexpected receptor mediated effects of N-methylcarbamylcholine on mouse M1 muscarinic receptor gene transfected cell line (M1Y1) that were not evident from biochemical studies with mouse and rat brain tissue where N-methylcarbamylcholine exhibited only nicotinic properties. Although N-methylcarbamycholine was devoid of muscarinic properties in mouse and rat brain preparations, as determined by phosphoinositide turnover and inhibition of [3H]QNB binding, it exhibited significant muscarinic characteristics in the transfected M1Y1 cell line. At a concentration of 10(-6) M or greater, N-methylcarbamycholine caused a transient increase in intracellular Ca2+ of 50 s duration that was reversible by atropine or pirezepine. The Ca(2+)-transient was not elicited by other nicotinic agents such as nicotine and N,N-dimethylcarbamylcholine, a close analogue of N-methylcarbamylcholine, with comparable affinity for nicotinic receptors and devoid of muscarinic activity. N-Methylcarbamylcholine also stimulated phosphoinositide turnover in M1Y1 cells with an estimated EC50 value 10 times greater than that of carbachol, and the effect was blocked by atropine. Both carbachol and N-methylcarbamycholine inhibited [3H]QNB binding in a concentration-dependent manner; however, the IC50 for carbachol was over two orders of magnitude greater than that observed in mouse and rat brain membranes. In considering possible explanations for the differential characteristics of N-methylcarbamylcholine in mouse and rat brain as compared to the transfected M1Y1 cells, it was concluded that the difference may be attributable to differences in the receptor-transduction coupling efficiency and the microenvironment of the muscarinic receptors.
Wang
D X
DX
Department of Biochemistry, University of Rochester Medical Center, NY 14642.
Lerner-Marmarosh
N
N
Sheu
S S
SS
Sharma
V
V
Jou
M J
MJ
Abood
L G
LG
D000311:Adrenal Glands / Q000378:metabolism; D000818:Animals; D001923:Brain Chemistry / Q000502:physiology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002217:Carbachol / Q000031:analogs & derivatives / Q000493:pharmacokinetics / Q000494:pharmacology; D002460:Cell Line; D008024:Ligands; D008566:Membranes / Q000378:metabolism; D051379:Mice; D010716:Phosphatidylinositols / Q000378:metabolism*; D011813:Quinuclidinyl Benzilate / Q000493:pharmacokinetics; D051381:Rats; D011976:Receptors, Muscarinic / Q000235:genetics* / Q000378:metabolism*; D014162:Transfection
D015220:Calcium Channels; D008024:Ligands; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; C053765:N-methylcarbamylcholine; D011813:Quinuclidinyl Benzilate; D002217:Carbachol