Fig. (3). Response of muscarinic receptor to its antagonist, pirenzepine Dose response curves of pirenzepine in CHO-M1 cells in the presence of 40 nM carbachol at 384-well format. Signal to background are 4.8 and 5.4, IC50 values are 224 nM and 200 nM using the first and second generation kits, respectively.○ BD™ High Performance Calcium Assay Kit (second generation).□ BD™ Calcium Assay Kit (first generation).