Inhibition of [3H]platelet activating factor (PAF) binding by Zn2+: A possible explanation for its specific PAF antiaggregating effects in human platelets

https://doi.org/10.1016/0003-9861(89)90241-5Get rights and content

Abstract

Zinc ions in the micromolar range exhibited a strong inhibitory activity toward platelet activating factor (PAF)-induced human washed platelet activation, if added prior to this lipid chemical mediator. The concentration of Zn2+ required for 50% inhibition of aggregation (IC50) was inversely proportional to the concentration of PAF present. The IC50 values (in μm) for Zn2+ were 8.8 ± 3.9, 27 ± 5.8, and 34 ± 1.7 against 2, 5, and 10 nm PAF, respectively (n = 3–6). Zn2+ exhibited comparable inhibitory effects on [3H]-serotonin secretion and the IC50 values (in μm) were 10 ± 1.2, 18 ± 3.5, and 35 ± 0.0 against 2,5, and 10 nm PAF, respectively (n = 3). Under the same experimental conditions, aggregation and serotonin secretion induced by ADP (5 μm), arachidonic acid (3.3 μm), or thrombin (0.05 U/ml) were not inhibited. Introduction of Zn2+ within 0–2 min after PAF addition not only blocked further platelet aggregation and [3H]serotonin secretion but also caused reversal of aggregation. Analysis of [3H]PAF binding to platelets showed that Zn2+ as well as unlabeled PAF prevented the specific binding of [3H]PAF. The inhibition of [3H]PAF specific binding was proportional to the concentration of Zn2+ and the IC50 value was 18 ± 2 μm against 1 nm [3H]PAF (n = 3). Other cations, such as Cd2+, Cu2+, and La3+, were ineffective as inhibitors of PAF at concentrations where Zn2+ showed its maximal effects. However, Cd2+ and Cu2+ at high concentrations exhibited a significant inhibition of the aggregation induced by 10 nm PAF with IC50 values being five- and sevenfold higher, respectively, than the IC50 for Zn2+, and with the IC50 values for inhibition of binding of 1 nm [3H]PAF being 5 and 19 times higher, respectively, than the IC50 for Zn2+. The specific inhibition of PAF-induced platelet activation and PAF binding to platelets suggested strongly that Zn2+ interacted with the functional receptor site of PAF or at a contiguous site.

References (40)

  • C.A. Demopoulos et al.

    J. Biol. Chem

    (1979)
  • S.D. Shukla et al.

    J. Biol. Chem

    (1983)
  • Y. Huo et al.

    Arch. Biochem. Biophys

    (1988)
  • M. Lagarde et al.

    Prostaglandins Med

    (1979)
  • D. Nunez et al.

    Eur. J. Pharmacol

    (1986)
  • J. Sugatani et al.

    Arch. Biochem. Biophys

    (1986)
  • R. Korth et al.

    Eur. J. Pharmacol

    (1987)
  • H. Homma et al.

    J. Biol. Chem

    (1987)
  • C.M. Chesney et al.

    Biochem. Biophys. Res. Commun

    (1985)
  • F.H. Valone

    Thromb. Res

    (1987)
  • S.B. Hwang

    J. Biol. Chem

    (1988)
  • S. Wagner et al.

    Biochim. Biophys. Acta

    (1980)
  • J. Patel et al.

    Brain Res

    (1982)
  • E.E. Mena et al.

    Brain Res

    (1985)
  • E.H. Huang et al.

    Life Sci

    (1986)
  • D. Findik et al.

    FEBS Lett

    (1988)
  • M.F. Crouch et al.

    Biochem. Biophys. Res. Commun

    (1988)
  • S.B. Hwang et al.

    Biochem. Pharmacol

    (1986)
  • J. Benveniste et al.

    C. R. Acad. Sci. Paris

    (1979)
  • F. Snyder

    Med. Res. Rev

    (1985)
  • Cited by (0)

    Supported by Grant AQ-887 from the Robert A. Welch Foundation.

    View full text