Nitric oxide delays atrial tachycardia-induced electrical remodelling in a sheep model

Abstract

Aims: Rapid atrial pacing for 1 week leads to decreased expression of endocardial nitric oxide (NO)-synthase and decreased NO concentrations. We hypothesized that increasing NO bioavailability may reduce electrical remodelling induced by atrial tachycardia. Methods and results: We examined the effect of molsidomine, a NO donor, and Nω-nitro-l-arginine methylester (l-NAME), a NO-synthase inhibitor, on electrical remodelling occurring during 4 h of rapid atrial pacing in sheep. Haemodynamic and electrophysiological parameters were measured at baseline, 1 h after the start of the infusion and before the start of pacing, and 2 and 4 h after pacing. We measured the effect of molsidomine on atrial monophasic action potentials (MAPs) in non-instrumented sheep and on l-type Ca2 currents and intracellular Ca2 concentration ([Ca2]i) transients in right atrial cells, isolated from control sheep. In control sheep, rapid atrial pacing shortened the atrial effective refractory period (AERP) by 12 ± 0.18 after 4 h, an effect that was unaffected by l-NAME. Infusion of molsidomine increased AERP at baseline (13.4 ± 1.04) and transiently attenuated pacing-induced AERP shortening (13.6 ± 0.1 at 2 h). Molsidomine tended to increase MAP duration by 20.7 ± 13.4 ms. Incubation of isolated atrial myocytes with NO donor 3-morpholino-sydnonimine (SIN-1) increased significantly l-type Ca2 current and [Ca2]i transients. Conclusion: Infusion of molsidomine, a NO donor, delayed shortening of the action potential during short-term rapid atrial pacing, by increasing [Ca2]i. Whereas the former could be protective against repetitive short episodes of atrial fibrillation, the latter might be detrimental in the long term. All rights reserved. © The Author 2011.