Figure 7.

Effect of NP-313 on thrombin- and A23187-induced Ca²⁺ release from internal stores and influx of extracellular Ca²⁺ in human platelets. Fura-2-loaded platelets were suspended in Tyrode's buffer containing creatining phosphate (CP; 10 mM), creatining phosphatase (CPK; 1 U·mL⁻¹) and indomethacin (100 µM). Effect of NP-313 on the release of the internally stored calcium in thrombin (0.1 U·mL⁻¹; A, left) and A23187 (8 µM; B, left) stimulated platelets. External calcium was not added to the platelet suspension; 1 mM EGTA was added 30 s prior to data collection (zero time). After 10 s, various concentrations of NP-313 were added; 20 s later, thrombin or A23187 was added. Effect of NP-313 on calcium influx initiated after mobilization of intracellular Ca²⁺ by thrombin (0.1 U·mL⁻¹; A, right) and A23187 (8 µM; B, right). Platelets were preincubated in the absence of extracellular Ca²⁺ and in the presence of 1 mM EGTA. Thrombin or A23187 was added at 10 s, and various concentrations of NP-313 were added to the platelets at 90 s. At 110 s, when [Ca²⁺]i was declining because of depletion of intracellular stores, 2 mM Ca²⁺ was added to the platelets. A representative of three experiments is shown. EGTA, ethylene glycol-bis (β-aminoethyl ether)-N,N,N′,N′-tetra acetic acid.