Mechanism of hydrogen sulfide mediated contraction in rat small pulmonary arteries

Abstract

The gas H2S (sulfide) causes a biphasic contraction of unknown mechanism in pulmonary arteries (PA). We assessed this mechanism in rings of rat 2nd order PA using myography to measure tension and NaHS as a source of sulfide. Reactive oxygen species (ROS) levels and the mitochondrial membrane potential (Δψ) were recorded using the indicators LO12 and TMRE, respectively. NaHS (500μM) evoked a small contraction and then a much larger 2nd contraction which gradually relaxed. The 2nd contraction was strongly reduced by 10μg/ml antimycin (AM) and 50μM dantrolene but was unaffected by 1μM rotenone (ROT). 10 or 30μM sulfide caused an immediate transient rise in [ROS]; at 100–1000μM this was followed by a 2nd larger rise in ROS which fell to baseline within ~10 min. The biphasic increases in tension and ROS had similar timecourses. The rise in [ROS] was slightly blocked by 1μM ROT but was almost abolished by 10μg/ml AM. 500 μM sulphide caused a triphasic effect on Δψ: a rapid very transient hyperpolarization was followed by a depolarization, a 2nd slower hyperpolarization, and then a return to baseline. Sulfide oxidation by the mitochondrial flavoprotein sulfide‐quinone oxoreductase (SQR), which is expressed in PA, has been shown in some cells to generate electrons that are passed to complex 3. We propose that metabolism of sulfide by SQR gives rise to a complex 3‐mediated increase in ROS that causes a contraction by activating the RyR.