Distinct spatio-temporal Ca2+ signaling elicited by integrin α2β1 and glycoprotein VI under flow

AbstractWe studied how integrin α2β1 and glycoprotein VI (GPVI) contribute to collagen-induced platelet activation under flow conditions by evaluating stable adhesion and intracellular Ca2+ concentration ([Ca2+]i) of FLUO 3-AM–labeled platelets perfused over acid-soluble type I or microfibrillar type VI collagen. Adhering platelets displayed 2 kinds of [Ca2+]i oscillations. Rapid α-like peaks were unaffected by the membrane-impermeable Ca2+ chelator ethyleneglycoltetraacetic acid but abolished by membrane-permeable BAPTA-AM. Longer-lasting γ-like peaks were always preceded by at least one α-like peak and abolished by intracellular or extracellular Ca2+ chelation. Inhibition of phosphatidylinositol 3-kinase or phospholipase C and modulation of cyclic nucleotides, but not blockage of adenosine diphosphate receptors, prevented both Ca2+ responses. Human or mouse platelets lacking GPVI function exhibited α-like but not γ-like Ca2+ peaks, whereas those lacking α2β1 showed markedly reduced to absent α-like and no γ-like Ca2+ peaks. Specific α2β1 ligation induced α-like but not γ-like peaks. Thus, α2β1 may generate Ca2+ signals that are reinforced by GPVI and required for subsequent longer-lasting Ca2+ oscillation mediated by GPVI through transmembrane ion flux. Our results delineate a GPVI-independent signaling role of α2β1 in response to collagen stimulation.