Fig. 4.

(A) Cell number titration of U-2 OS hERG cells treated with or without haloperidol. The signal-to-basal (S/B) ratios defined by with (+) and without (−) haloperidol in the thallium flux assay for 500, 1000, 2000, and 4000 cells/well were 2.7-, 2.6-, 3.1-, and 3.1-fold, respectively. (B) Comparison of wash and no-wash protocols. For the wash protocol, cells in suspension were loaded in Opti-MEM medium containing 2% serum, FluxOR dye, and probenecid for 60 min at room temperature. Cells were then pelleted, washed, and plated at a density of 2000 cells/3 μl in assay buffer containing probenecid. Immediately after plating, cells were treated with 50 μM haloperidol or DMSO. For the no-wash protocol, cells were plated at a density of 2000 cells/3 μl in Opti-MEM containing 2% serum and allowed to adhere to the bottom of the plate for 4 h at 37 °C. Cells were then loaded with 1 μl of dye mixture and incubated at room temperature prior to being assayed. The S/B ratios were 3.1 and 4.2 for wash and no-wash, respectively. Each data point represents the mean + S.E.M. (n = 4).