Evidence for a functional vasodilatatory role for hydrogen sulphide in the human cutaneous microvasculature.

KEY POINTS: Hydrogen sulphide (H2 S) is vasoprotective, attenuates inflammation and modulates blood pressure in animal models; however, its specific mechanistic role in the human vasculature remains unclear. In the present study, we report the novel finding that the enzymes responsible for endogenous H2 S production, cystathionine-γ-lyase and 3-mercaptopyruvate sulphurtransferase, are expressed in the human cutaneous circulation. Functionally, we show that H2 S-induced cutaneous vasodilatation is mediated, in part, by tetraethylammonium-sensitive calcium-dependent potassium channels and not by ATP-sensitive potassium channels. In addition, nitric oxide and cyclo-oxygenase-derived byproducts are required for full expression of exogenous H2 S-mediated cutaneous vasodilatation. Future investigations of the potential role for H2 S with respect to modulating vascular function in humans may have important clinical implications for understanding the mechanisms underlying vascular dysfunction characteristic of multiple cardiovascular pathologies. ABSTRACT: The present study aimed to identify the presence of cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate sulphurtransferase (3-MST), which endogenously produce hydrogen sulphide (H2 S), and to functionally examine the mechanisms of H2 S-induced vasodilatation in the human cutaneous microcirculation. CSE and 3-MST were quantified in forearm skin samples from 5 healthy adults (24 ± 3 years) using western blot analysis. For functional studies, microdialysis fibres were placed in the forearm skin of 12 healthy adults (25 ± 3 years) for graded infusions (0.01-100 mm) of sodium sulphide (Na2 S) and sodium hydrogen sulphide (NaHS). To define the mechanisms mediating H2 S-induced vasodilatation, microdialysis fibres were perfused with Ringer solution (control), a ATP-sensitive potassium channel (KATP ) inhibitor, an intermediate calcium-dependent potassium channel (KCa ) inhibitor, a non-specific KCa channel inhibitor or triple blockade. To determine the interaction of H2 S-mediated vasodilatation with nitric oxide (NO) and cyclo-oxygenase (COX) signalling pathways, microdialysis fibres were perfused with Ringer solution (control), a non-specific NO synthase inhibitor, a non-selective COX inhibitor or combined inhibition during perfusion of increasing doses of Na2 S. CSE and 3-MST were expressed in all skin samples. Na2 S and NaHS elicited dose-dependent vasodilatation. Non-specific KCa channel inhibition and triple blockade blunted Na2 S-induced vasodilatation (P < 0.05), whereas KATP and intermediate KCa channel inhibition had no effect (P > 0.05). Separate and combined inhibition of NO and COX attenuated H2 S-induced vasodilatation (all P < 0.05). CSE and 3-MST are expressed in the human microvasculature. Exogenous H2 S elicits cutaneous vasodilatation mediated by KCa channels and has a functional interaction with both NO and COX vasodilatatory signalling pathways.