ADP Initiates Phosphorylation Of Platelet Myosin Light Chain (MLC), A 40,000 Dalton Protein (40P) And Actin Binding Protein (ADP) Independent Of Secretion

J Gerrard, R Carroll
1981 Thrombosis and Haemostasis  
The mechanism by which ADP initiates platelet shape change and granule centralization is unknown. Recent studies of platelet proteins have provided evidence that raised intracellular calcium produces its effect by promoting protein phosphorylation. We have studied the influence of ADP on the phosphorylation of platelet proteins in both platelet rich plasma (PRP) and washed platelets, using the incorporation of 32p to identify phosphorylated proteins. 10u M ADP was found to cause a 2-5 fold
more » ... ased phosphorylation of MLC, 40P and ABP. Pretreatment of the platelets with 100uM ASA prevented secretion of serotonin but decreased the ADP induced phosphorylation only by about 1/3. 2u M ADP stirred with platelets in PRP caused reversible aggregation without secretion and was associated with increased phosphorylation of MLC, 40P and ABP. The results show that ADP can cause phosphorylation of platelet proteins independent of secretion. We suggest ADP raises intracellular calcium levels to cause the phosphorylations which initiate contractile protein interactions to produce shape change and granule centralization. The results also show that platelet granule secretion must be dependent on other factors in addition to phosphorylation of these proteins.
doi:10.1055/s-0038-1652234 fatcat:4tt74xvcefb3pc4mear56kypru