Click to download
| 197P London, UK Pharmacology 2016 |
Role of pannexin channels in mediating endothelium dependent vasorelaxation in PSA
Introduction: Pannexins are a newly discovered family of proteins with sequence homology to innexins1 that form channels in cell membranes to allow ATP to pass to act as an intercellular messenger. It has been suggested that Panx1 plays a role in endothelium-dependent regulation of arterial tone 2. This study examined the expression and function of pannexins in porcine splenic arteries.
Methods: PSA were prepared for isometric tension recording in oxygenated Krebs solution .The presence of Panx proteins was studied by Western blotting and immunohistochemistry. The effect of Panx1 inhibitors on endothelium-dependent vasorelaxation induced by bradykinin (BK) was determined following preconstriction with (U46619), a TxAâ‚‚ mimetic. Tone was raised to 50% of the KCl response with U46619. Once stable tone was achieved responses to the endothelium-dependent vasorelaxant, BK, were assessed in the absence and presence of the nitric oxide synthase inhibitor L-NAME (100 µM) and/ or cyclooxygenase inhibitor, indomethacin (10 µM). Similar experiments examined the effect of pannexin inhibitors Mefloquine (2X10-5M) and probenecid (2X10-4M). Vasorelaxant responses were expressed as a percentage of U46619-induced contraction. Data were presented as means ± SEM. Statistical analysis were performed by two-way ANOVA followed by a Bonferroni post-hoc test P<0.05 was considered significant.
Results: Both Panx1 and Panx2 proteins were present in PSA and on the vascular endothelium. In functional studies under control conditions, BK produced a concentration-dependent vasorelaxation (log EC50= -9.09± 0.3; Rmax = -83.62 ± 8%, n = 6. The response to BK was decreased significantly in the presence of L-NAME (log EC50 = -8.5 ± 0.2; Rmax = -25.7 ± 6%, n = 6), unaffected by indomethacin (log EC50 =-8.77 ± 0.60; Rmax = -81.1 ± 12.8%,n = 6) but reduced by Indomethacin and L-NAME together (log EC50 =-8.74± 0.4 ; Rmax = -20.34 ± 7% , n =6). BK response were not affected by mefloquine (2X10-5M) The maximum response to BK was -51.72 ± 7% (control) and -58.84 ± 10% in the presence of mefloquine (2x10-5M). The maximum response to BK was -54.29 ± 4.5% (control) and -50.18 ± 5% in the presence of probenecid (2x10-4M) ,the sensitivity was -8.35± 0.2 (control) and -8.32± 0.2 (probenecid (2x10-4M)) n =7.
Conclusion: The data show that BK induces a vasorelaxation in the PSA mostly by releasing nitric oxide. The nitric oxide-mediated response was not affected by pannexin inhibitors and so these proteins are not involved in mediating endothelium dependent responses in the PSA.