Date Published: April 1, 2018
Publisher: American Physiological Society
Author(s): Jesus Prieto-Lloret, Vladimir A. Snetkov, Yasin Shaifta, Inmaculada Docio, Michelle J. Connolly, Charles E. MacKay, Greg A. Knock, Jeremy P. T. Ward, Philip I. Aaronson.
Application of H2S (“sulfide”) elicits a complex contraction in rat pulmonary arteries (PAs) comprising a small transient contraction (phase 1; Ph1) followed by relaxation and then a second, larger, and more sustained contraction (phase 2; Ph2). We investigated the mechanisms causing this response using isometric myography in rat second-order PAs, with Na2S as a sulfide donor. Both phases of contraction to 1,000 μM Na2S were attenuated by the pan-PKC inhibitor Gö6983 (3 μM) and by 50 μM ryanodine; the Ca2+ channel blocker nifedipine (1 μM) was without effect. Ph2 was attenuated by the mitochondrial complex III blocker myxothiazol (1 μM), the NADPH oxidase (NOX) blocker VAS2870 (10 μM), and the antioxidant TEMPOL (3 mM) but was unaffected by the complex I blocker rotenone (1 μM). The bath sulfide concentration, measured using an amperometric sensor, decreased rapidly following Na2S application, and the peak of Ph2 occurred when this had fallen to ~50 μM. Sulfide caused a transient increase in NAD(P)H autofluorescence, the offset of which coincided with development of the Ph2 contraction. Sulfide also caused a brief mitochondrial hyperpolarization (assessed using tetramethylrhodamine ethyl ester), followed immediately by depolarization and then a second more prolonged hyperpolarization, the onset of which was temporally correlated with the Ph2 contraction. Sulfide application to cultured PA smooth muscle cells increased reactive oxygen species (ROS) production (recorded using L012); this was absent when the mitochondrial flavoprotein sulfide-quinone oxoreductase (SQR) was knocked down using small interfering RNA. We propose that the Ph2 contraction is largely caused by SQR-mediated sulfide metabolism, which, by donating electrons to ubiquinone, increases electron production by complex III and thereby ROS production.
Hydrogen sulfide (H2S, hereafter referred to as sulfide) typically acts as a vasodilator but in some arteries causes constriction or a complex response that exhibits both constricting and dilating phases (26). In rat pulmonary arteries (PAs), for example, application of 1 mM sulfide (as NaHS) to PAs preconstricted with norepinephrine caused a brief transient constriction followed by a relaxation and then a second and more sustained constriction (25). This response resembles the effect of hypoxia in these arteries, and based on this similarity and other observations, Olson and coworkers (25, 27) proposed that hypoxic pulmonary vasoconstriction (HPV) is due to a build-up of cellular sulfide concentration ([sulfide]) during hypoxia resulting from an inhibition of its oxidative metabolism.
It has previously been shown that application of 1,000 μM NaHS to preconstricted rat PAs induces a unique triphasic effect on tension consisting of two phases of contraction separated by a relaxation (25). This response bears some resemblance to HPV in these arteries. Based on this similarity and other evidence, Olson et al. (27) proposed that HPV is triggered by an increase in the intracellular concentration of sulfide, which would be predicted to occur under hypoxic conditions. We have recently reported that antagonists of the enzymes that synthesize sulfide do not inhibit HPV, which argues against this model (30). The present study was carried out as a complementary approach to examining this hypothesis by determining to what extent the mechanisms underlying the sulfide response, which remain obscure, resemble those of HPV.
J. Prieto-Lloret, V. Snetkov, and Y. Shaifta were supported by Wellcome Trust Programme Grant 087776 (to J. P. Ward and P. I. Aaronson). M. J. Connolly and C. E. MacKay were supported by PhD Studentships from British Heart Foundation Grants FS/05/117/19967 (to P. I. Aaronson) and FS/12/43/29608 (to G. A. Knock). I. Docio was supported by an Erasmus Traineeship.
No conflicts of interest, financial or otherwise, are declared by the authors.
J.P.-L., V.A.S., Y.S., I.D., M.J.C., C.E.M., G.A.K., and P.I.A. performed experiments; J.P.-L., V.A.S., Y.S., M.J.C., and P.I.A. analyzed data; J.P.-L., V.A.S., J.P.W., and P.I.A. interpreted results of experiments; J.P.-L., V.A.S., and Y.S. prepared figures; J.P.-L., V.A.S., J.P.W., and P.I.A. edited and revised manuscript; J.P.-L., V.A.S., Y.S., I.D., M.J.C., C.E.M., G.A.K., J.P.W., and P.I.A. approved final version of manuscript; P.I.A. conceived and designed research; P.I.A. drafted manuscript.