D. Lasne et al., DIFFERENT ABILITIES OF THROMBIN RECEPTOR ACTIVATING PEPTIDE AND THROMBIN TO INDUCE PLATELET CALCIUM RISE AND FULL RELEASE REACTION, Thrombosis and haemostasis, 74(5), 1995, pp. 1323-1328
Synthetic peptides (TRAP or Thrombin Receptor Activating Peptide) corr
esponding to at least the first five aminoacids of the new N-terminal
tail generated after thrombin proteolysis of its receptor are effectiv
e to mimic thrombin. We have studied two different TRAPs (SFLLR, and S
FLLRN) in their effectiveness to induce the different platelet respons
es in comparison with thrombin. Using Indo-1/AM-labelled platelets, th
e maximum rise in cytoplasmic ionized calcium was lower with TRAPs tha
n with thrombin. At threshold concentrations allowing maximal aggregat
ion (50 mu M SFLLR, 5 mu M SFLLRN and 1 nM thrombin) the TRAPs-induced
release reaction was about the same level as with thrombin, except wh
en external calcium was removed by addition of 1 mM EDTA. In these con
ditions, the dense granule release induced by TRAPs was reduced by ove
r 60%, that of lysosome release by 75%, compared to only 15% of reduct
ion in the presence of thrombin. Thus calcium influx was more importan
t for TRAPs-induced release than for thrombin-induced release. At stro
ng concentrations giving maximal aggregation and release in the absenc
e of secondary mediators (by pretreatment with ADP scavengers plus asp
irin), SFLLRN mobilized less calcium, with a fast return towards the b
asal level and induced smaller lysosome release than did thrombin. The
results further demonstrate the essential role of external Calcium in
triggering sustained and full platelet responses, and emphasize the m
ajor difference between TRAP and thrombin in mobilizing [Ca2+](i). Thu
s, apart from the proteolysis of the seven transmembrane receptor, ano
ther thrombin binding site or thrombin receptor interaction is require
d to obtain full and complete responses.