THE HUMAN MUSCARINIC M1 ACETYLCHOLINE-RECEPTOR, WHEN EXPRESSED IN CHOCELLS, ACTIVATES AND DOWN-REGULATES BOTH G(Q)ALPHA AND G(11)ALPHA EQUALLY AND NONSELECTIVELY

CHO cells express both of the phosphoinositidase C-linked G-proteins G (q) and G11 . G11alpha is some 2.5-fold more highly expressed than G(q )alpha in membranes of these cells. Following transfection and stable expression of CHO cells with DNA encoding the human muscarinic M1 acet ylcholine (HM1) receptor, chronic treatment of the cells with the chol inergic agonist carbachol resulted in down-regulation of membrane leve ls of both G(q)alpha and G11alpha. Dose-response curves to carbachol p roduced identical EC50 values for agonist-induced down-regulation of t he two G-proteins and both were down-regulated with the same time cour se. These data indicate that the HM1 receptor interacts with and activ ates both G(q)alpha and G11alpha equivalently and non-selectively in a whole cell system in which the receptor has access to both G-proteins .