Cartoon model of regulation of WPB exocytosis. (I) Newly formed WPBs recruit Rab proteins (Rab27A and Rab3A/B/D) and their effectors Slp4-a, Munc13-4, and MyRIP/Myosin Va.^{22,23,25,27-29}  (II) WPBs are anchored to the actin cytoskeleton via Myosin Va and MyRIP.^27,28  (III) STXBP1 links WPBs to the SNAREs (syntaxin-2/3) via Slp4-a and Rab27A, whereas STXBP3 (Munc18c) associates with syntaxin-4.⁴⁶  (IV) SNARE complex assembly of syntaxins with WPB-associated VAMP 3/8,⁵⁹  potentially facilitated by Munc13-4.²⁵  Fusion of WPB and plasma membrane and dispersal of WPB cargo into vascular lumen.