~3H-QNB Saturation analysis revealed typical single-site saturation curve inCHO cell line transfected with cDNA of m1

m2or m4 receptors

with Hill numbersof nearly 1. Inhibition study of ~3H-QNB binding to muscarinic receptors inmembranes of these cells revealed that PZP had an affinity of m1>m4>m2 in theCHO cells

while METH had an affinity of m2>m4>m1. Using the m2 transfectedcells

carbachol could partially inhibit the foskolin induced cAMP elevation

indicating that there was a complete pathway for the trasduction of signals raised byagonist stimulation of M2 receptors. The time course of M2 receptor density in m2transfected CHO cell lines showed a peak value at about 48h and then dropped downgradually. The above results suggest that the cell lines could be used as models forthe study of structure and function of single subtypes of muscarinic receptors as wellas for screening of drugs.