Cloned M1 muscarinic receptors mediate both adenylate cyclase inhibition and phosphoinositide turnover.
The rat M1 muscarinic receptor gene was cloned and expressed in a rat cell line lacking endogenous muscarinic receptors. Assignment of the cloned receptors to the M1 class was pharmacologically confirmed by their high affinity for the M1-selective muscarinic antagonist pirenzepine and low affinity for the M2-selective antagonist AF-DX-116. Guanylyl imidodiphosphate [Gpp(NH)p] converted agonist binding sites on the receptor, from high-affinity to the low-affinity state, thus indicating that the cloned receptors couple to endogenous G-proteins. The cloned receptors mediated both adenylate cyclase inhibition and phosphoinositide hydrolysis, but by different mechanisms. Pertussis toxin blocked the inhibition of adenylate cyclase (indicating coupling of the receptor to inhibitory G-protein), but did not affect phosphoinositide turnover. Furthermore, the stimulation of phosphoinositide hydrolysis was less efficient than the inhibition of adenylate cyclase. These findings demonstrate that cloned M1 receptors are capable of mediating multiple responses in the cell by coupling to different effectors, possibly to different G-proteins.
Stein
R
R
Department of Biochemistry, George S. Wise Faculty of Life Sciences, Tel Aviv University, Israel.
Pinkas-Kramarski
R
R
Sokolovsky
M
M
D000109:Acetylcholine / Q000378:metabolism; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D003001:Cloning, Molecular; D019204:GTP-Binding Proteins / Q000378:metabolism; D010095:Oxotremorine / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011976:Receptors, Muscarinic / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism
D000067956:Adenylyl Cyclase Inhibitors; D010716:Phosphatidylinositols; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; D010095:Oxotremorine; D001285:Atropine; D002217:Carbachol; D019204:GTP-Binding Proteins; D000109:Acetylcholine