Working model of G protein signaling-dependent EC vWF secretion. vWF secretion occurs via Gα12-αSNAP interaction resulting in constitutive (basal) exocytosis (left). On thrombin stimulation (right), the rate of vWF secretion is potentiated by Gαq-dependent and Ca²⁺-induced activation of α-SNAP and by Gα12-RhoA-actin-dependent delivery of WPBs to the plasma membrane.