Summary
ATP released by activated platelets can serve as a positive feedback machinery to
amplify platelet responses by activating P2X1 receptors. It has, however, not been defined how P2X1 activities influence thromboxane A2 (TXA2)-stimulated platelet functional responses. Our aim was to elaborate the molecular
mechanisms of P2X1 engagements in TXA2-induced platelet secretion and aggregation. P2X1 inhibition by 1 µM NF449 inhibited platelet P-selectin expression induced by a low
concentration of the TXA2 analogue U46619 (0.3 µM) (32.0 ± 2.0% vs 43.4 ± 3.0%; n=5; p<0.05). p38 inhibition
by SB203580, but not ERK inhibition by U0126, elicited a similar inhibition by NF499.
The combination of NF449 and SB203580 provided, however, no additive effects. U46619-induced
platelet aggregation was similarly decreased by NF449 and SB203580 alone or incombination,
and by P2×1 pre-desensitisation with α,β-Me-ATP. U46619 caused rapid and reversible
P2×1-dependent p38 phosphorylation. However, the P2X1-p38 pathway mainly enhanced mild platelet activation by U46619, because α,β-Me-ATP
supplementation or p38 blockade had no effect on intense platelet activation induced
by a higher concentration of U46619 (3 µM). In conclusion, P2×1 activation, via p38
signalling, potentiates platelet activation initiated by low doses of U46619. Hence,
the P2X1-induced p38 signalling promotes more robust platelet activation in response to mild
platelet stimuli.
Keywords
Platelets - ATP - P2X
1
- p38 - thromboxane A
2