THE INTERACTION OF THE ENANTIOMERS OF ACECLIDINE WITH SUBTYPES OF THEMUSCARINIC RECEPTOR

The pharmacological activity of the enantiomers of aceclidine was inve stigated in Chinese hamster ovary cells transfected with the M(1) thro ugh M(5) subtypes of the muscarinic receptor and also in the rat heart and parotid gland that express primarily M(2) and M(3) receptors, res pectively. When measured by stimulation of phosphoinositide hydrolysis in Chinese hamster ovary cells transfected with the M(1), M(3) and M( 5) muscarinic subtypes, the potency of S-(+)-aceclidine was approximat ely 2- to 4-fold greater than that of R-(-)-aceclidine, whereas the ma ximal response of the R-(-)-isomer was only 44 to 64% that of the S-()-isomer. When measured by inhibition of forskolin-stimulated cyclic A MP accumulation in Chinese hamster ovary cells transfected with the M( 2) and M(4) muscarinic subtypes, the potency of S-(+)-aceclidine was a pproximately 3.5-fold greater than that of R-(-)-aceclidine. In cells transfected with the M(2) muscarinic receptor, the maximal responses o f the enantiomers were the same, whereas the maximal response of R-(-) -aceclidine was 86% that of S-(+)-aceclidine in cells transfected with the M(4) muscarinic subtype. The activities of the enantiomers of ace clidine at native M(2) and M(3) muscarinic receptors coupled to inhibi tion of adenylyl cyclase activity in the heart and stimulation of phos phoinositide hydrolysis in the parotid gland, respectively, were simil ar to those observed in Chinese hamster ovary cells transfected with t he corresponding receptor subtypes. We devised a simple quantitative m ethod for using our data in Chinese hamster ovary cells to predict the relative potencies of agonists in a more sensitive assay in which the agonists produce a full maximum response. By using this method, we we re able to predict the relative potencies of the enantiomers for elici ting contractions in the guinea pig ileum, an M(3) muscarinic response , from their activity in Chinese hamster ovary cells transfected with the M(3) muscarinic subtype. Our method of analysis should have applic ation in a variety of studies in which transfected cells are used to d etermine the pharmacological activity of agonists.