Myosin IIa-deleted ECs exhibit impaired mature WPB distribution and decreased cAMP-induced VWF secretion. (A) Cardiac endothelial cells isolated from WT and iEMKO mice and immunostained with antibodies against VWF (yellow) and paxillin (magenta). F-actin was labeled with phalloidin (cyan). (Right) Magnified insets. (B) Quantitative analysis of the number of FAs per cell as in A (n = 15; **P < .01, 3 independent experiments). (C) Confocal images of WT and iEMKO CECs immunostained with antibodies against VWF (yellow) and Rab27a (magenta). F-actin was labeled with phalloidin (cyan). Arrows indicate WPBs. (Right) Magnified insets. (D) Number of Rab27a-positive WPBs along stress fibers as in C (**P < .01; ***P < .001). (E) VWF secretion in CECs isolated from WT and iEMKO mice with epinephrine stimulation (n = 12; **P < .01, Student’s t-test; mean ± standard deviation; scale bars, 5 μm).