title: ADP-induced platelet shape change and mobilization of cytoplasmic ionized calcium are mediated by distinct binding sites on platelets: 5'-p-fluorosulfonylbenzoyladenosine is a weak platelet agonist.
abstract: Platelet stimulation with ADP results in several responses, including shape change, increase in cytoplasmic ionized calcium concentration [Ca2+]i, an inhibition of adenylate cyclase. 5'-p-Fluorosulphonyl benzoyladenosine (FSBA), which covalently labels an ADP binding site on platelets, blocks platelet shape change but not the inhibition of cyclic AMP levels by ADP, whereas p-chloromercuribenzenesulfonate (pCMBS), a nonpenetrating thiol reagent, has the opposite effects. We examined the effect of FSBA and pCMBS on ADP-induced increase in [Ca2+]i using platelets loaded with fluorescent Ca2+ indicators quin2 and fura-2. FSBA (50 to 200 mumol/L) induced a dose-dependent rise in [Ca2+]i, indicating that it is a weak platelet agonist. Under conditions of covalent labeling of the ADP binding sites, FSBA (50 to 100 mumol/L) did not inhibit the ADP-induced increase in [Ca2+]i or its inhibition of adenylate cyclase, whereas pCMBS (up to 1 mmol/L) abolished both these responses but not shape change. These findings suggest that ADP-induced Ca2+ mobilization and inhibition of adenylate cyclase are mediated by platelet binding sites distinct from those mediating shape change.
mesh_terms: D002731:4-Chloromercuribenzenesulfonate / Q000494:pharmacology; D000241:Adenosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000494:pharmacology*; D001665:Binding Sites; D001792:Blood Platelets / Q000166:cytology* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000037:antagonists & inhibitors / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D006801:Humans; D009994:Osmolar Concentration
chemical_list: D002731:4-Chloromercuribenzenesulfonate; D000244:Adenosine Diphosphate; C010959:5'-(4-fluorosulfonylbenzoyl)adenosine; D000242:Cyclic AMP; D000241:Adenosine; D002118:Calcium