Weibel-Palade bodies (WPBs) are rod-shaped organelles, stored as heterogeneous populations in the endothelium, containing cargo that is rapidly released upon demand 1. WPBs have numerous constituents that play roles in primary haemostasis, inflammation and angiogenesis such as von Willebrand Factor (vWF), P-selectin and angiopoietin-2, respectively 2,3. Several functionally distinct endothelial agonists induce WPB trafficking and exocytosis by raising intracellular Ca2+. It has been previously speculated that endothelial cells can selectively secrete WPB cargo in an agonist-appropriate manner, however, the underlining mechanisms are poorly understood 4. The aim of the project was to examine differential WPB trafficking using high-resolution cellular imaging alongside intracellular Ca2+ measurements and biochemical techniques. In order to investigate differential WPB trafficking, we treated HUVECs with histamine and thrombin (both potent WPB secretagogues). After 5 mins we observed that histamine-treated cells (immunostained with vWF as a marker for WPBs), but not thrombin, evoked clustering of a subpopulation of WPBs that were positive for Rab46 (CRACR2A-a: a newly identified Ca2+-sensing GTPase 5) to the microtubule organising centre (MTOC). Therefore, we reasoned that histamine may evoke differential WPB trafficking, the release of P-selectin is necessary for a histamine response and P-selectin resides in WPBs that do not contain the pro-angiogenic tie-2 ligand, angiopoietin-2 3. Image analysis revealed that in basal and stimulated conditions, Rab46 localised to WPBs that are devoid of P-selectin (control 8.32% ± 0.38, histamine 7.38% ±1.87) but contain angiopoietin-2 (control 27.58% ±1.48, histamine 32.27% ±1.52). Stimulation of HUVECs with histamine, promoted significant MTOC localisation of WPBs carrying angiopoietin-2 (control 0.53 ± 0.02, histamine 0.73 ± 0.03; 2-way ANOVA p value < 0.001) but not P-selectin (control 0.48 ± 0.03, histamine 0.59 ± 0.03; 2-way ANOVA p value = 0.23). In addition, in the absence of stimulation, only angiopoietin-2, but not P-selectin, is confined to the MTOC when co-localised with constitutively active Rab46 (Q604L). Quantification of P-selectin at the cell surface in HUVECs, transfected with control or Rab46 siRNA, demonstrated that histamine-evoked surface release of P-selectin was Rab46-independent. However, Angiopoietin-2 was decreased in supernatants from histamine-stimulated cells where Rab46 was depleted. Further investigation revealed an inhibitory effect on angiopoietin-2 protein levels as well as high-resolution imaging showed that in cells where Rab46 was depleted, angiopoietin-2 was no longer localised to WPBs. Taken together these findings support that Rab46 is a novel regulator that couples inflammatory stimuli to differential trafficking of WPBs and that it may be necessary for angiopoietin-2 recruitment.