CHARACTERIZATION OF MUSCARINIC ACETYLCHOLINE-RECEPTORS EXPRESSED BY AN ATRIAL CELL-LINE DERIVED FROM A TRANSGENIC MOUSE-TUMOR

The properties of muscarinic acetylcholine receptors in the cell line MCM1, derived from an SV40 T-antigen-induced atrial tumor in a transge nic mouse, were determined. Binding studies using the nonselective mus carinic antagonist [H-3]quinuclidinyl benzilate, the M1-selective anta gonist pirenzepine, and the M2-selective antagonist AFDX-116 indicate that the receptors have the pharmacological properties of the cardiac (M2) receptor subtype. The receptors could be immunoprecipitated with a monoclonal antibody specific for the cardiac receptor, thus confirmi ng the identity of the receptors expressed in these cells. The types o f G proteins expressed in the cells were determined by Northern blot a nalyses: mRNA encoding the alpha subunits of G(s), G(o), and G(i-2), b ut not G(i-1) or G(i-3), were detected, consistent with previous obser vations of neonatal mammalian atria. The muscarinic receptors were fun ctionally active, as demonstrated by the ability of the agonist to sti mulate phosphoinositide turnover and to inhibit adenylyl cyclase activ ity. The availability of a mammalian atrial cell line that continues t o express the appropriate functionally coupled subtype of muscarinic r eceptor may provide a useful system for the investigation of the regul ation of expression and function of cardiac muscarinic receptors.