Effect of ST1926, nicardipine, and the combination of the 2 agrents on the levels of intracellular calcium in NB4 cells incubated in the presence or absence of calcium in the medium. Following prelodaing with the calcium fluorescent indicator FURA-2, NB4 cells (1 × 10⁶/mL) were resuspended in calcium-containing (+Ca⁺⁺) or calcium-free (-Ca⁺⁺) PBS. Cells were placed in a cuvette under stirring at 37°C and changes in fluorescence were measured continuously with the use of a spectrophotofluorometer. NB4 cells were preincubated with 5 mM nickel chloride (Ni⁺⁺; A); 100 μM verapamil (B); the indicated concentrations of nicardipine (C-E); or nitrendipine, nicardipine, and nimodipine (F) prior to addition of ST1926 at the concentration of 1 μM. The left arrow indicates the addition of Ni⁺⁺, verapamil, or nicardipine, whereas the right arrow indicates the addition of ST1926. Each tracing is representative of at least 2 independent experiments run in triplicate. In panel F, the results are expressed as the mean ± SD of 3 replicate cultures. °Significantly higher than the vehicle-treated group (P < .01 according to the Student t test). *Significantly lower than the ST1926-treated group (P < .01 according to the Student t test).