Abstract
Platelet activation was elevated by changes in the fluorescence anisotropy of the sulfhydryl-reactive fluorescent probe, (5-[2-(iodoacetyl) aminacetyl]aminonaphthalene-1-sulfonic acid. The membrane-permeable fluorophore was shown to bind to a multitude of cytoplasmic and membrane proteins. Platelets were stimulated by addition of thrombin, arachidonic acid or ADP under conditions that did not induce aggregation. A sudden increase in the fluorescence anisotropy, r of moderate degree (25–33%) occurred during the first 60 s after exposure of platelets to the aggregating agents and was sustained during the entire period of observation (15–18 min). Phenylmethylsulfonyl thrombin was unable to produce these changes in fluorescence anisotropy. Preincubation of platelets with colchicine reduced r within 30–60 s after platelets were exposed to thrombin. These findings are interpreted as an indication of a general decrease in the ‘motional freedom’ of the fluorophores and indirectly their ligand molecules.
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