Hydrogen Sulfide Plays a Key Role in the Inhibitory Neurotransmission to the Pig Intravesical Ureter

According to previous observations nitric oxide (NO), as well as an unknown nature mediator are involved in the inhibitory neurotransmission to the intravesical ureter. This study investigates the hydrogen sulfide (H(2)S) role in the neurogenic relaxation of the pig intravesical ureter. We have performed western blot and immunohistochemistry to study the expression of the H(2)S synthesis enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), measurement of enzymatic production of H(2)S and myographic studies for isometric force recording. Immunohistochemical assays showed a high CSE expression in the intravesical ureter muscular layer, as well as a strong CSE-immunoreactivity within nerve fibres distributed along smooth muscle bundles. CBS expression, however, was not consistently observed. On ureteral strips precontracted with thromboxane A(2) analogue U46619, electrical field stimulation (EFS) and the H(2)S donor P-(4-methoxyphenyl)-P-4-morpholinylphosphinodithioic acid (GYY4137) evoked frequency- and concentration-dependent relaxations. CSE inhibition with DL-propargylglycine (PPG) reduced EFS-elicited responses and a combined blockade of both CSE and NO synthase (NOS) with, respectively, PPG and N(G)-nitro-L-arginine (L-NOARG), greatly reduced such relaxations. Endogenous H(2)S production rate was reduced by PPG, rescued by addition of GYY4137 and was not changed by L-NOARG. EFS and GYY4137 relaxations were also reduced by capsaicin-sensitive primary afferents (CSPA) desensitization with capsaicin and blockade of ATP-dependent K(+) (K(ATP)) channels, transient receptor potential A1 (TRPA(1)), transient receptor potential vanilloid 1 (TRPV(1)), vasoactive intestinal peptide/pituitary adenylyl cyclase-activating polypeptide (VIP/PACAP) and calcitonin gene-related peptide (CGRP) receptors with glibenclamide, HC030031, AMG9810, PACAP(6–38) and CGRP(8–37), respectively. These results suggest that H(2)S, synthesized by CSE, is involved in the inhibitory neurotransmission to the pig intravesical ureter, through an NO-independent pathway, producing smooth muscle relaxation via K(ATP) channel activation. H(2)S also promotes the release of inhibitory neuropeptides, as PACAP 38 and/or CGRP from CSPA through TRPA(1), TRPV(1) and related ion channel activation.