Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, C80
Mechanism of hydrogen sulphide mediated contraction in rat small pulmonary arteries
J. Prieto-Lloret1, V. Snetkov1, M. J. Connolly1, J. P. Ward1, P. I. Aaronson1
1. King's College London, London, United Kingdom.
The gas H2S (hereafter ‘sulphide’) may act as an endogenous vasodilator in the systemic circulation. In pulmonary arteries, however, sulphide elicits a biphasic contraction with an unknown mechanism. We assessed the mechanism of this contraction in rat 2nd order pulmonary arteries (PA), using NaHS as a source of sulphide. Techniques used included recording of isometric tension in PA rings mounted in a small vessel myograph and measurement of reactive oxygen species (ROS) levels in segments of PA using the luminescent ROS indicator LO12 (10 μM). NaHS (500 μM) evoked a complex increase in tension, comprising a small contraction followed by a second and larger contraction which gradually relaxed. The contraction, measured at its peak, was inhibited by 95 ± 5% by the mitochondrial complex 3 blocker antimycin (10μg/ml, n = 6; p <0.05; paired t test) by 64 ± 7% (mean ± SEM) by the anti-oxidant TEMPOL (3 mM, n = 3; p <0.05 ), and by 78 ± 10 % by the RyR blocker dantrolene (50 μM, n = 4; p <0.05). In 5 experiments, low concentrations (10 or 30 μM) of sulphide caused an immediate short-lived increase in [ROS] measured using LO12. At higher concentrations (100, 300 and 1000 μM), this initial response was followed by a second increase in ROS which developed and then decayed to baseline within 5 minutes. The time courses of the biphasic increases in tension and ROS were similar. The increase in ROS was attenuated by rotenone (1 μM, 29 ± 15% inhibition, n = 5; ns), and very markedly suppressed by a combination of rotenone (1 μM) and antimycin (10μg/ml) (83 ± 6% inhibition, n = 6; p <0.05). There is evidence that sulphide is oxidised by the mitochondrial membrane flavoprotein sulphide-quinone oxoreductase (SQR) and that this reaction generates electrons which are donated to ubiquinone and are then passed onto complex 3 (Hildebrandt & Grieshaber, 2008). Given the marked block by antimycin of both sulphide-induced tension development and the increase of ROS it evokes, we propose that metabolism of sulphide by SQR is giving rise to a complex 3-mediated increase in ROS through this mechanism, and that this causes a contraction by activating the RyR. In light of the proposal that sulphide levels rise in PA during hypoxia (Olson & Whitfield 2010), we further speculate that increases in cellular [sulphide] during hypoxia promote its oxidation by SQR and donation of electrons to complex 3, and that this could account for the apparent paradox that hypoxia may be associated with an increased ROS production by complex 3 in pulmonary artery smooth muscle cells (Waypa et al., 2001).
Where applicable, experiments conform with Society ethical requirements