Isolation, sequence, and functional expression of the mouse M1 muscarinic acetylcholine receptor gene

A genomic clone encoding the gene for the mouse M1 muscarinic acetylcholine receptor has been isolated, placed under the control of the zinc-inducible mouse metallothionein promoter, and transfected into mouse Y1 adrenal cells. The receptor concentration was about 300 fmol/mg membrane protein in the absence of zinc and could be increased to 4000 fmol/mg membrane protein in the presence of increasing concentrations of zinc. The receptor expressed in zinc-induced cells exhibits the high affinity binding for quinuclidinyl benzilate, atropine, and pirenzepine expected of the M1 muscarinic receptor. The M1 receptor when expressed in Y1 or L cells is physiologically active, as measured by agonist-dependent stimulation of phosphatidylinositol metabolism, but does not inhibit forskolin stimulation of cAMP accumulation. In contrast, a cloned M2 muscarinic receptor when expressed in Y1 cells is able to inhibit forskolin stimulation of cAMP accumulation, but is unable to stimulate phosphatidylinositol metabolism. The stimulation of phosphatidylinositol metabolism mediated by the M1 receptor was not altered by prior treatment of Y1 cells with concentrations of islet-activating protein sufficient to eliminate M2 receptor-mediated inhibition of adenylate cyclase. The cloned M1 receptor gene thus exhibits both the pharmacological and physiological properties expected of the M1 muscarinic acetylcholine receptor. In addition, these results indicate that different subtypes of the muscarinic receptor are coupled to different physiological responses.