ACETYLSALICYLIC ACID ENHANCES PURINERGIC RECEPTOR‐MEDIATED OUTWARD CURRENTS IN RAT MEGAKARYOCYTES

Abstract

Megakaryocytes (MKs) as platelet progenitor cells are a relevant model for platelet reactivity. Patch clamp techniques were used to analyze effects of acetylsalicylic acid (ASA), a COX‐1 inhibitor antithrombotic agent, on purinergic receptor‐mediated Ca++ activated K+ outward currents in rat MKs. Bone marrow MKs were incubated in 1mM ASA (ASA and sodium salicylate IC50 plasma value 2.5 mM; USP Convention. 2000). Using a K+ rich internal solution, currents were recorded in response to 10 μM ATP, 10 μM ADP or 5 μM 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. In different cells, 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 blocker), were stimulated with 2MeSADP. The dose response curve to 2MeSADP was shifted to the left by both drugs, suggesting increased MK reactivity. Current amplitude was increased by 30 μM IP3 added to the internal solution; this was also attenuated by ASA, suggesting that ASA might affect the P2Y‐IP3‐calcium signaling pathway. These findings may be relevant to the increasingly reported ASA resistance during clinical treatment.