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Effect of calcium and calcium antagonists on (/sup 3/H)-Paf-acether binding to washed human platelets

Journal Article · · Thromb. Res.; (United States)
; ; ; ;

(/sup 3/H)-Platelet activating factor (Paf-acether, 1-O-octadecyl-2-acetyl-sn-glycero-3-phosphocholine) binds to washed human platelets in a specific, dose-dependent, and saturable manner. Scatchard analysis reveals a high affinity site with a KD value of 0.25 +/- 0.033 nM (245 +/- 30 sites per platelet), and a second low affinity site with a KD value of 9.22 +/- 1.17 nM (1616 +/- 165 sites per platelet). Binding to the high affinity site is independent of buffer calcium concentration, inhibited on an equimolar basis by unlabelled 1-O-octadecyl-Paf-acether, but remains unchanged in the presence of 1-O-octadecyl-lyso-Paf-acether. The relative inhibitory effect of four calcium antagonists on (/sup 3/H)-Paf-acether high affinity binding correlates closely with their respective anti-aggregatory activity against Paf-acether induced responses in human PRP; order of potency being (+)-cis diltiazem greater than (+/-)-verapamil greater than (-)-cis diltiazem greater than nifedipine. In the case of (+)-cis diltiazem, the effect is competitive, stereo-specific and progressively reversed by addition of calcium (1.0 mM and 5.0 mM). A close spatial relationship may thus exist between the Paf-acether receptor and membrane calcium channels in the human platelet.

Research Organization:
Searle Research and Development, Buckinghamshire, England
OSTI ID:
5682121
Journal Information:
Thromb. Res.; (United States), Journal Name: Thromb. Res.; (United States) Vol. 2; ISSN THBRA
Country of Publication:
United States
Language:
English

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Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
AFFINITY
ALKALINE EARTH METALS
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL EFFECTS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BLOOD COAGULATION FACTORS
BLOOD PLATELETS
BODY FLUIDS
BUFFERS
CALCIUM
COAGULANTS
DOSE-RESPONSE RELATIONSHIPS
DRUGS
ELEMENTS
HEMATOLOGIC AGENTS
KINETICS
LABELLED COMPOUNDS
MATERIALS
MEMBRANE PROTEINS
METALS
ORGANIC COMPOUNDS
PROTEINS
REACTION KINETICS
RECEPTORS
TRITIUM COMPOUNDS