Concentration dependence of ATRA-induced modulation of calcium pump expression. HL-60 cells were treated for 4 days with various concentrations of ATRA and calcium pump expression; NBT reduction by the cells was also determined. (A) Immunostaining for SERCA 2b and SERCA_PLIM with the IID8 and PLIM430 antibodies, respectively. (B) NADPH oxidase activity of the cells as measured by NBT reduction. (C and D) Densitometric analysis of SERCA_PLIM and SERCA 2b expression. Data represent the mean ± SEM of 5 experiments.