Evidence for P(2)-purinoceptors contribution in H(2)O(2)-induced contraction of rat aorta in the absence of endothelium

Abstract

Objective: H(2)O(2) can contract many arteries, however the underlying mechanisms are not fully understood. This study aims to test whether H(2)O(2)-induced vasoconstriction could be functionally attributed to the activation of P(2)-purinoceptors in rat aorta and to explore its possible signaling mechanisms.

Methods: Isometric tension recording of H(2)O(2) and ATP-induced contractions of rat aortic rings were compared in the absence or presence of various pharmacological tools to identify their possible common signaling pathways.

Results: Both H(2)O(2) and ATP induced transient phasic contractions in a concentration-dependent manner (1-1000 microM). Removal of endothelium potentiated the contractile responses to H(2)O(2) and to ATP. H(2)O(2) (30 microM)-induced phasic contraction could be abolished by catalase (800 U/ml), but not affected by SOD (150 U/ml), DMSO (5 mM) and apyrase (5 U/ml), suggesting no involvement of O(2)(-), hydroxyl free radicals and ATP release. Also, several receptor antagonists including phentolamine, atropine, methysergide and chlorpheniramine (each 3 microM) were without effect on H(2)O(2) (30 microM)-induced phasic contraction, suggesting no involvement of typical neurotransmitter release. However, both H(2)O(2) (30 microM) and ATP (1 mM)-induced phasic contractions not only presented homologous desensitization, but also showed heterogeneous desensitization. Furthermore, the phasic contractions in response to H(2)O(2) (30 microM) or ATP (100 microM) could be inhibited or abolished in a concentration dependent manner by RB-2 and suramin (10-100 microM), two widely used P(2)-purinoceptor antagonists, with only partial inhibition by Evans blue (300 microM), a moderately selective P(2x) receptor blocker, or by alpha-beta-methylene-ATP (100 microM), a selective P(2x) receptor desensitizer. On the other hand, both H(2)O(2) (30 microM) and ATP (100 microM)-induced phasic contractions were also attenuated, to different degree, by inhibitors of several enzymes including PLC, PKC, PLA(2) and cyclooxygenase. Lastly, removal of extracellular Ca(2+) or pretreatment with procaine (10 mM) and dantrolene (30 microM), two putative intracellular Ca(2+) release blockers, or with Ni(2+) (100 microM) and tetrandrine (5 microM), two Ca(2+) channel blockers, all significantly inhibited H(2)O(2) and ATP-induced contractions. However, nifedipine (1 microM), a voltage-dependent L-type Ca(2+) channel blocker, was without effect.

Conclusions: Our results demonstrate that H(2)O(2)-induced phasic contraction of rat aorta involves, at least in part, the activation of P(2)-purinoceptors in the aortic smooth muscle cells