ABSTRACT
Dipartimento di Psichiatria, Neurobiologia, Farmacologia e Biotecnologie, Università di Pisa; via Bonanno, 6, I-56126 Pisa, Italy.
Hydrogen sulphide (H2S) is now emerging as an important endogenous modulator [1] with important implications in the homeostatic control of the cardiovascular system, where it is mainly biosynthesized by cystathionine -lyase from the aminoacid L-Cysteine. Among the several important effects in the cardiocirculatory regulation, H2S shows a vasorelaxing activity which is known to be mediated, at least in part, by the activation of ATP-sensitive potassium channels (KATP) of vascular smooth muscle cells [2,3]. Nevertheless, it widely accepted that other types of potassium channel can play a role, but presently this aspect is poorly investigated. In this study, the vasorelaxing activity of the H2S-donor NaHS was tested on rat thoracic aortic rings. Furthermore, its electrophysiological effects were indirectly evaluated on human aortic smooth muscle cells (HASMC) by means of membrane potential sensitive fluorescent dye DiBAC4(3).
As expected, NaHS produced vasorelaxing effects on rat thoracic aortic rings precontracted with KCl 25mM. These responses were strongly reduced by an higher concentration of KCl (60mM), which is used as a non-specific inhibitor of the effects of almost all the potassium channel activators. Even Glibenclamide, a KATP channel blocker, antagonized the vasorelaxing effect but only partially. In order to evaluate the possible involvement of voltage-operated potassium channels (Kv), the effects of NaHS were tested also in the presence of the Kv-blocker tetraethylammonium chloride (TEA). TEA caused a significant Kv1.3 Margatoxin (selective blocker of Kv1.3) did not affect the functional effects of NaHS, while Linopirdine and XE-991 (both selective blockers of Kv7) exhibited a significant antagonism, suggesting a possible involvement of Kv7 potassium channels.
In order to strengthen the hypothesis emerged by the functional study on rat thoracic aorta, the influence of NaHS on the membrane potential of HASMCs was evaluated through the use of DiBAC4(3). NaHS caused a membrane hyperpolarization, which was not affected by Margatoxin and was only slightly influenced by
4-aminopyridine. On the contrary, NaHS-induced membrane hyperpolarizing effects were clearly antagonized by the Kv7 blockers Linopirdine and XE-991. These experimental results suggest the hypothesis that - together with KATP channels - also Kv7 potassium channels can be physiologically involved in the vascular effects of H2S.
Acknowledgements
This work has been supported by the “Regional Health Research Program 2009” of Regione Toscana, Italy.
References
[1] Martelli A, Testai L, Breschi MC, Blandizzi C, Virdis A, Taddei S, Calderone V. Hydrogen sulphide: novel opportunity for drug discovery. Med Res Rev 2011; in press (published on-line DOI: 10.1002/med.20234).
[2] Zhao W, Zhang J, Lu Y, Wang R. The vasorelaxant effect of H2S as a novel endogenous gaseous K(ATP) channel opener. EMBO J 2001; 20: 6008-6016.
[3] Jiang B, Tang G, Cao K, Wu L, Wang R. Molecular Mechanism for H2S-Induced Activation of K(ATP) Channels. Antiox Redox Signal 2010; 12: 1167-1178.