Rab27a and Munc13-4 recruitment to perforin granules is dependent on myosin function. Resting NK cells were treated with PMA and ionomycin alone or in combination with ML-9 at the indicated concentrations for 20 minutes at 37°C, followed by fixation, permeabilization, and labeling. Colocalization of perforin with Rab27a (A) or Munc13-4 (B) was calculated as Pearson correlation coefficient, r, using the JACOP plugin in ImageJ, with 10 to 15 cells per condition analyzed from each of 2 healthy donors. Mean values are plotted; error bars represent SD.