Réaction de libération plaquettaire induite par la phospholipase C

Human washed‐platelet suspensions are incubated with 7.5 μg/ml (final concentration) of phospholipase C from Clostridium welchii for 0 to 5 min. The enzyme is previously heated for 12 min at 56°C in presence of 5 mMCaCl 2 for removing thermosensitive haemolysin. Under these conditions, the platelets release ATP, ADP and lactate dehydrogenase with following results.1 After 3 or 5 min, 19–47% of ATP, 17–71% of ADP, but only 0–8.3% of lactate dehydrogenase are released. 2 ATP/ADP ratio of released nucleotides (0.6–1.6) is lower than platelet ratio (1.5–2.3), which increases in the course of incubation (3.0–6.0). 3 With [8‐ 14 C]adenine labelled platelets, little amounts of radioactive ATP or ADP appear in the supernatants. Specific activities of extracellular ATP and ADP are 10 to 20 times lower than those of intracellular ATP and ADP. In the platelets, radioactivity of ADP remains unchanged, but radioactive ATP is metabolized to IMP, inosine and hypoxanthine.It is concluded that the bulk of released nucleotides originates from the “non‐metabolic pool” and is located in platelet dense bodies. Phospholipase C induces a slow cell lysis and a rapid secretory process (release reaction). Little hydrolysis occurs in the time of release reaction (5–10%). With 30‐min incubation, 32.4% of phospholipids are hydrolysed, with preferential splitting of phosphatidylcholine (41.5–69.2%), sphingomyelin (30.4–66.3%) and to a lesser extent phosphatidylethanolamine (13.2–32.4%). Splitting of phosphatidylserine and phosphatidylinositol does not occur. A relation between phospholipid hydrolysis and release reaction seems as yet difficult to stay.