The interactions of platelets and liposomes with the tripeptide argini
ne-glycine-aspartic acid (RGD) as a surface ligand (RGD liposomes) wer
e studied. The results suggest that the presence of the RGD ligand on
the liposomes results in receptor-mediated mixing of lipid and aqueous
contents of the liposomes and platelets. Mixing of the lipid and aque
ous contents of RGD liposomes with platelets is approximately 4-9 time
s and 3-4 times greater than that for unlabeled liposomes, respectivel
y. Measurements of the cytoplasmic free Ca2+ concentration in platelet
s, [Ca2+](i), show that the RGD liposomes have little effect on [Ca2+]
(i). (C) 1996 Academic Press, Inc.