Comparative analysis of P2X₁ receptor function in platelets, neutrophils, and mononuclear leukocytes. The indicated types of human blood cells were loaded with fura-2 and assayed for agonist-induced changes in cytosolic [Ca²⁺] as described under Materials and Methods. Each experiment was repeated twice using different preparations of blood cells and yielded similar results. For ease of graphic presentation, segments from certain continuous records have been deleted as indicated by braces { }; the duration of each deleted segment is noted. (A) Platelets were suspended in normal basal salt solution (BSS) containing 130 mmol/L NaCl, 1 mmol/L CaCl₂, and 2.5 U/mL apyrase. The cells were first stimulated with 30 μmol/L αβ-methylene ATP (αβme-ATP). After about 3 minutes, the cells were rechallenged with additional αβ-methylene ATP (60 μmol/L final) and then serially stimulated with 30 μmol/L ADP, followed by 1 U/mL thrombin. (B) Platelets were suspended in reduced Na-BSS containing 40 mmol/L NaCl, 90 mmol/L NMG-Cl, 1 mmol/L CaCl₂, and 2.5 U/mL apyrase. The platelets were serially stimulated with 30 μmol/L αβ-methylene ATP (twice), 30 μmol/L ADP, and 1 U/mL thrombin. (C) Neutrophils were suspended in reduced Na-BSS containing 40 mmol/L NaCl, 90 mmol/L NMG-Cl, 1 mmol/L CaCl₂, and 2.5 U/mL apyrase. They were stimulated with 30 μmol/L αβ-methylene ATP, followed by 1 μmol/L FMLP. Another sample (suspended in the same medium) was stimulated by 30 μmol/L ATP. (D) Mononuclear leukocytes were suspended in reduced Na-BSS containing 40 mmol/L NaCl, 90 mmol/L NMG-Cl, 1 mmol/L CaCl₂, and 2.5 U/mL apyrase. They were stimulated with 30 μmol/L αβ-methylene ATP, followed by 5 μg/mL concanavalin A.