FIGURE 6.

Proposed model of CD38 activation in platelets. Thrombin receptor, protease-activated receptor (PAR), couples with G protein and stimulates PLC, producing two second messengers, IP₃ and diacylglycerol (DAG). IP₃-mediated Ca²⁺ release along with diacylglycerol activates PKC, which induces the phosphorylation of MHCIIA. The Phospho-MHCIIA makes complexes with CD38 via Lck, which results in internalization of CD38 and subsequently allows the formation of cADPR and NAADP in platelets. Phospholipid scramblase (PLSCR), a Ca²⁺-dependent enzyme, flips the PS from inner membrane to the outer membrane.