Fig. (8). Comparison of first and second generation BD™ PBX calcium assay kit in 1536-well format A. CHO-M1 cells treated with and without 1 µM carbacol using BDTM High Performance PBX Calcium Assay Kit in absence of probenecid. Signal to background is 3.1, and Z’ value is 0.84 (n = 12).B. CHO-M1 cells treated with and without 1 µM carbachol using BDTM PBX Calcium Assay Kit in absence of probenecid. Signal to background is 2.1, and Z’ value is 0.79.