Optimization of cell plating density. TRPM7-HEK293 cells (positive control, blue circles) and WT-HEK293 cells (negative controls, black squares) were plated at (A) 30,000, (B) 60,000, and (C) 120,000 cells/well. Each data point is the mean ± SD of 48 replicate wells for TRPM7-HEK293 cells and 24 replicate wells for WT-HEK293 cells, and Z′ factor values (red triangles) are plotted.