Characterization of the effect of the adenosine agonist cyclohexyladenosine on platelet activating factor-induced increases in [Ca2+]i in human platelets in vitro

M. A. Javors, M. Liu, B. S. Cuvelier, C. L. Bowden

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Previous studies have shown that adenosine agonists acting at A-2 receptors Inhibit platelet aggregation. Since an increase in cytosolic Ca2+ concentration (Δ[Ca2+]i) is closely associated with the time frame of platelet aggregation, we have examined the effect or adenosine receptor function on induced increases of [Ca2+]i by a potent platelet activator, piatelet activating factor (PAF). We loaded washed platelets with Fura-2, then induced increases in [Ca2+]i with various concentrations of PAF, and then determined EC50 values (PAF concentration at half-maximal response) and values for maximal response of Δ[Ca2+]i (max-Δ[Ca2+]i). The EC50 for PAF-Δ[Ca2+]i was 112 ± 37 (SD) pM and the max-Δ[Ca2+]i was 284 ± 138 (SD) nM. Our results show that PAF-Δ[Ca2+]i was inhibited in a non-competitive manner by the adenosine receptor agonist cyclohexyladenosine (CHA) with an IC50 of 14.9 μM. This inhibition was partially reversed by theophylline, an adenosine receptor antagonist, with an IC50 of 19 μM. Based on the results of these studies together with evidence from other research groups that platelets do not possess A-1 receptors, our results suggest that CHA inhibited PAF-Δ[Ca2+]i in platelets through an activation of A-2 receptors.

Original languageEnglish (US)
Pages (from-to)647-653
Number of pages7
JournalCell Calcium
Issue number10
StatePublished - Jan 1 1990


ASJC Scopus subject areas

  • Physiology
  • Molecular Biology
  • Cell Biology

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