Thrombin binding to GP Ib-IX-V expressed on leukemic mouse fibroblasts cells is inhibited by HK. Mouse fibroblast cell line transfected with GP Ib-IX-V complex was tested for the ability to bind thrombin with or without added HK. The first bar shows biotinylated thrombin (590 nmol/L) binding to untransfected cells. Thrombin binding to cells transfected with and expressing GP Ib-IX-V complex in the absence (bar 2) or presence (bar 3) of 1.3 μmol/L HK is shown. The results are the mean ± SEM of 10 determinations. The binding to L cells and the effect of HK addition to L-Ib-IX-V cells are statistically different from the binding to L-Ib-IX-V cells alone (P < .0001).