Figure 1.

Extracellular chloride is required for efficient platelet activation. (a) Washed platelets were stimulated by increasing concentrations of thrombin or 1 µg mL⁻¹ CRP-XL in the presence of 151 mM (black) or 1 mM (gray) [Cl⁻]_o. Representative aggregation traces are shown for each condition (ai). Maximum aggregation (aii) and the initial rate of aggregation (aiii) were calculated for each condition. (b) In the presence of 2 mM [Ca²⁺]_o, [Cl⁻]_o substitution continued to reduce the initial rate of thrombin-evoked aggregation. (c) The sensitivity of thrombin-evoked (0.1 U mL⁻¹) aggregation to Cl⁻ was assessed by increasing [Cl⁻]_o from 1 to 151 mM in 30 mM increments. Representative traces (ci), maximum (cii) and initial rate of thrombin-induced (0.1 U mL⁻¹) aggregation (ciii) for each [Cl⁻]_o are shown. The rate of aggregation increased across the concentration range with an EC₅₀ = 46.5 ± 23.3 mM. Data are representative of a minimum of four independent experiments. Thrombin and CRP-XL data sets were analyzed by two-way ANOVA and Student’s t test, respectively.