title: Acetylsalicylic acid enhances purinergic receptor-mediated outward currents in rat megakaryocytes.
abstract: Purinergic receptor activation increases cytosolic Ca(2+) concentration in a fluctuating fashion, triggering oscillatory outward Ca(2+)-activated K(+) currents in rat megakaryocytes (MKs). Whole cell and nystatin-perforated patch-clamp techniques were used to analyze changes in ionic conductance in MK with acetylsalicylic acid (ASA), a cyclooxygenase-1 inhibitor and antithrombotic agent. MKs are a model for platelet reactivity, particularly in ASA treatment failure (ASA resistance). Freshly isolated MKs were incubated 30 min in the absence or presence of 1 mM ASA. Using a K(+)-rich internal solution, we recorded outward currents in response to 10 microM ATP, 10 microM ADP, and 5 microM 2-methyl-thio-ADP (2MeSADP) in the voltage-clamp mode. Agonist-induced currents decreased in amplitude over time, but this decline was attenuated by ASA in both continuous and repeated agonist challenge, indicating increased MK reactivity with ASA treatment. In separate experiments, heterologous desensitization was observed when MKs were stimulated with ADP after exposure to a thromboxane receptor agonist (U46619), indicating cross talk between thromboxane and purinergic pathways. Different cells, treated with ASA or MRS2179 (P2Y1 receptor antagonist), were stimulated with 2MeSADP. The dose-response curve was shifted to the left in both cases, suggesting increased MK reactivity. ASA also caused an increased interval between currents (delay). ASA attenuated desensitization of purinergic receptors and increased delay, again suggesting cross talk between purinergic and thromboxane pathways. These findings may be relevant to ASA resistance, because individual variations in sensitivity to the multiple effects of ASA on signaling pathways could result in insensitivity to its antiplatelet effects in some patients.
authors.affiliation: Dept. of Physiology and Biophysics, Georgetown Univ., Columbia, Washington, DC 20057, USA. jpy9@georgetown.edu
authors.forename: José P
authors.initials: JP
authors.lastname: Young
authors.forename: Jacob
authors.initials: J
authors.lastname: Beckerman
authors.forename: Stefano
authors.initials: S
authors.lastname: Vicini
authors.forename: Adam
authors.initials: A
authors.lastname: Myers
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001241:Aspirin / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004351:Drug Resistance; D005343:Fibrinolytic Agents / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D007700:Kinetics; D008297:Male; D008533:Megakaryocytes / Q000187:drug effects* / Q000378:metabolism; D008564:Membrane Potentials; D009761:Nystatin / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010975:Platelet Aggregation Inhibitors / Q000494:pharmacology*; D011188:Potassium / Q000378:metabolism*; D024681:Potassium Channels, Calcium-Activated / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020239:Receptor Cross-Talk; D011983:Receptors, Purinergic / Q000187:drug effects* / Q000378:metabolism; D017482:Receptors, Thromboxane / Q000037:antagonists & inhibitors / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013873:Thionucleotides / Q000378:metabolism
chemical_list: D016861:Cyclooxygenase Inhibitors; D005343:Fibrinolytic Agents; D007476:Ionophores; C111914:N(6)-methyl-2'-deoxyadenosine 3',5'-diphosphate; D010975:Platelet Aggregation Inhibitors; D024681:Potassium Channels, Calcium-Activated; D011983:Receptors, Purinergic; D017482:Receptors, Thromboxane; D013873:Thionucleotides; D009761:Nystatin; C002480:methylthio-ADP; D000244:Adenosine Diphosphate; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D000255:Adenosine Triphosphate; D001241:Aspirin; D011188:Potassium; D002118:Calcium