NSF-2 peptides inhibit both Ca²⁺-induced and agonist-induced platelet granule secretion. Platelets with¹⁴C-serotonin–loaded dense granules were preincubated with saponin and with or without NSF-2 peptides (1.5 mmol/L). Granule secretion was induced by increasing the free Ca²⁺-concentration to 10 μmol/L (Ca²⁺⁾, with or without 1 U/mL thrombin (thr). Secretion was measured by counting radioactivity in the cell supernatants (see Materials and Methods; mean ± SD, n = 2; representative of 2 independent experiments with similar results).