Muscarinic acetylcholine receptors belong to a superfamily of seven-™-domain receptors that interact with G-proteins to initiate intracellular responses. Five muscarinic receptor subtypes have been identified and named from M1 to M5. The M2 muscarinic receptor couples to Gi/o to inhibit cAMP production. GenScript co-transfected human M2 with Ga15 in the CHO-K1 which supports high levels of recombinant M2 expression on the cell surface and contains high levels of Ga15 to couple the receptor to the calcium signaling pathway.