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Human platelets release a paf‐acether: Acetylhydrolase similar to that in plasma
Author(s) -
Korth Ruth,
Bidualt Jocelyne,
Palmantier Remi,
Benveniste Jacques,
Ninio Ewa
Publication year - 1993
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02536639
Subject(s) - platelet , thrombin , chemistry , lysis , clinical chemistry , biochemistry , platelet activating factor , microbiology and biotechnology , lactic dehydrogenase , lactate dehydrogenase , enzyme , chromatography , endocrinology , biology , immunology
Intact washed human platelets aggregated in response to paf‐acether (paf) and did not metabolize [ 3 H]paf at concentrations up to 10 nM. However, when platelets were lysed by exposure to pH 9.5, resulting in 37.5±2.5% (mean ±SD, n=3) lactic dehydrogenase (LDH) release, 20.5±5.7% of the radioactivity was detected as labeled lyso paf and 5.7±3.1% as labeled alkylacylglycerophosphocholine. When platelets were aggregated with 0.5 IU/mL thrombin or high concentrations of paf (100 nM), they released a part of their acetylhydrolase without releasing LDH. In supernatants obtained from aggregated platelets, 21±2% or 10±2% (n=3), respectively, of the total platelet acetylhydrolase activity was detected vs. none in supernatants of resting cells. The release of acetylhydrolase was concentration‐and time‐dependent and paralleled the release of PF 4, a marker for α‐granules. The acetylhydrolase affinity for paf (K m ) measured in sonicates of resting and thrombin‐activated platelets was 8.3±1.5 μM vs. 10.6±1.5 μM, n=5, n.s. in a “Mann Whitney” test. The latter K m was slightly but significantly different ( P <0.05, n=5) from that of the thrombin‐released acetylhydrolase (7.9 ±1.5 μM) and that of the latter was itself different from plasma acetylhydrolase (5.3±0.5, P <0.05, n=5). Addition of plasma (acid‐treated to inactivate acetylhydrolase) decreased the K m value of supernatant acetylhydrolase to 6.1±1.4 μM. All preparations of acetylhydrolase exhibited similar pH requirements and sensitvity to various inhibitors. Thus paf and thrombin cause release of acetylhydrolase from platelets in parallel with release of the α‐granule marker PF4. This phenomenon might represent a protective mechanism against paf‐mediated effects in thrombotic and cardiovascular diseases.