Effects of DCB, bepridil, or Ro31-8220 on platelet granule secretion. (A) Effects on dense granule secretion. Washed platelets (3 × 10⁵/μL) labeled with [¹⁴C]5-HT were stimulated by 0.1 U/mL thrombin in the presence of DCB (a), bepridil (b), or Ro31-8220 (c). Relative amounts of [¹⁴C]5-HT released from platelets for 15 minutes after stimulation were determined by liquid scintillation and normalized to 100% for 5-HT release from platelets stimulated in the absence of inhibitors. Results are the mean ± SD. (B) Effects on -granule secretion. Washed platelets (1 × 10⁵/μL) were suspended in modified Tyrode Hepes buffer containing 1 mmol/L CaCl₂(columns 1, 2, 5 to 7), 2 mmol/L EGTA (column 3), or TMA-buffer (column 4). The platelets were stimulated with (columns 2 to 7) or without (column 1) 0.1 U/mL thrombin in the presence of 10 μmol/L DCB (column 5), 80 μmol/L bepridil (column 6), or 8 μmol/L Ro31-8220 (column 7). Relative amounts of bound ¹²⁵I-S12 (anti–P-selectin MoAb) were normalized to 100% value for S12 binding to platelets stimulated with 0.1 U/mL thrombin in the absence of inhibitors (column 2).