NO is a reversible inhibitor of the thrombin-induced shape change. Aspirin-treated and gel-filtered human platelets in the presence of CP/CPK were stimulated with thrombin (0.01 U/mL) and exposed to NO (1.1 × 10^-10 mol NO/mL/min, as indicated), and platelet shape change is consistent with a decrease in light transmission (see “Materials and methods”). (A) Shape change induced by thrombin (0.01 U/mL). (B) NO infusion was started 1 minute prior to the addition of thrombin. Two minutes after the addition of thrombin, NO infusion was stopped, and 2 minutes later, infusion of NO was restarted. Aliquots were withdrawn (i-vii) for the analysis of platelet resistive-volume and platelet morphology (Figures 2 and 3). Traces are from a single experiment, representative of 6.