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 (H₂S) role in the neurogenic relaxation of the pig intravesical ureter. We have performed western blot and immunohistochemistry to study the expression of the H₂S synthesis enzymes cystathionine γ-lyase (CSE) and cystathionine β-synthase (CBS), measurement of enzymatic production of H₂S 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 A₂ analogue U46619, electrical field stimulation (EFS) and the H₂S 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 H₂S 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 (TRPA₁), transient receptor potential vanilloid 1 (TRPV₁), 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 H₂S, 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. H₂S also promotes the release of inhibitory neuropeptides, as PACAP 38 and/or CGRP from CSPA through TRPA₁, TRPV₁ and related ion channel activation.

Underlying mechanisms involved in progesterone-induced relaxation to the pig bladder neck

Progesterone increases bladder capacity and improves the bladder compliance by its relaxant action on the detrusor. A poor information, however, exists concerning to the role of this steroid hormone on the bladder outflow region contractility. This study investigates the progesterone-induced action on the smooth muscle tension of the pig bladder neck. To this aim, urothelium-denuded bladder neck strips were mounted in myographs for isometric force recordings and for simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)]i) and tension. On phenylephrine (PhE)-precontracted strips, progesterone produced concentration-dependent relaxations only at high pharmacological concentrations. The blockade of progesterone receptors, nitric oxide (NO) synthase, guanylyl cyclase, large conductance Ca(2+)-activated K(+) (BKCa) or ATP-dependent K(+) (KATP) channels reduced the progesterone relaxations. The presence of the urothelium and the inhibition of cyclooxygenase (COX), intermediate- and small-conductance Ca(2+)-activated K(+) channels failed to modify these responses. In Ca(2+)-free potassium rich physiological saline solution, progesterone inhibited the contraction to CaCl2 and to the L-type voltage-operated Ca(2+) (VOC) channel activator BAY-K 8644. Relaxation induced by progesterone was accompanied by simultaneous decreases in smooth muscle [Ca(2+)]i. These results suggest that progesterone promotes relaxation of pig bladder neck through smooth muscle progesterone receptors via cGMP/NO pathway and involving the activation of BKCa and KATP channels and inhibition of the extracellular Ca(2+) entry through L-type VOC channels.

Endogenous hydrogen sulfide has a powerful role in inhibitory neurotransmission to the pig bladder neck

PURPOSE

We investigated the possible involvement of H2S in nitric oxide independent inhibitory neurotransmission to the pig bladder neck.

MATERIALS AND METHODS

We used immunohistochemistry to determine the expression of the H2S synthesis enzymes cystathionine γ-lyase and cystathionine β-synthase. We also used electrical field stimulation and myographs for isometric force recordings to study relaxation in response to endogenously released or exogenously applied H2S in urothelium denuded, phenylephrine precontracted bladder neck strips under noradrenergic, noncholinergic, nonnitrergic conditions.

RESULTS

Cystathionine γ-lyase and cystathionine β-synthase expression was observed in nerve fibers in the smooth muscle layer. Cystathionine γ-lyase and cystathionine β-synthase immunoreactive fibers were also identified around the small arteries supplying the bladder neck. Electrical field stimulation (2 to 16 Hz) evoked frequency dependent relaxation, which was decreased by DL-propargylglycine and abolished by tetrodotoxin (blockers of cystathionine γ-lyase and neuronal voltage gated Na(+) channels, respectively). The cystathionine β-synthase inhibitor O-(carboxymethyl)hydroxylamine did not change nerve mediated responses. The H2S donor GYY4137 (0.1 nM to 10 μM) induced potent, concentration dependent relaxation, which was not modified by neuronal voltage gated Na(+) channels, or cystathionine γ-lyase or cystathionine β-synthase blockade.

CONCLUSIONS

Results suggest that endogenous H2S synthesized by cystathionine γ-lyase and released from intramural nerves acts as a powerful signaling molecule in nitric oxide independent inhibitory transmission to the pig bladder neck.

Mechanisms involved in testosterone-induced relaxation to the pig urinary bladder neck

OBJECTIVES

Testosterone replacement therapy improves bladder capacity in urinary tract dysfunction. There is no information, however, about the role of this steroid hormone on the muscle tension of the bladder outflow region. The current study investigated the mechanisms underlying the testosterone-induced action in the pig bladder neck.

METHODS

Urothelium-denuded bladder neck strips were mounted in myographs for isometric force recordings and for simultaneous measurements of intracellular Ca(2+) concentration ([Ca(2+)](i)) and tension. The relaxations to testosterone, the non-aromatizable metabolite 4,5α-dihydrotestosterone (DHT) and electrical field stimulation (EFS) were carried out on phenylephrine (PhE)-precontracted strips.

RESULTS

Testosterone and DHT evoked similar concentration-dependent relaxations only at very high pharmacological concentrations. The presence of the urothelium and the inhibition of intracellular androgenic receptor (AR), aromatase, 5α-reductase, nitric oxide (NO) synthase, guanylyl cyclase, cyclooxygenase (COX), large-, intermediate- and small-Ca(2+)-activated K(+) channels or ATP-dependent K(+) channels failed to modify the testosterone relaxations. Neuronal voltage-gated Ca(2+) (VOC) channels and voltage-gated K(+) (K(V)) channel blockers potentiated these responses. EFS evoked frequency-dependent relaxations, which were not changed by threshold concentrations of testosterone. In Ca(2+)-free potassium rich physiological saline solution, testosterone inhibited the contractions induced by CaCl(2) and the L-type VOC channel activator (±)-BAY K 8644. Relaxations elicited by testosterone were accompanied by simultaneous decreases in smooth muscle [Ca(2+)](i).

CONCLUSIONS

Testosterone produces relaxation of the pig urinary bladder neck through mechanisms independent of urothelium, AR, aromatase, 5α-reductase, NO synthase, guanylyl cyclase, COX and K(+) channels. Testosterone-induced relaxation is produced via the inhibition of the extracellular Ca(2+) entry through L-type VOC channels.

Endothelin ET(B) receptors are involved in the relaxation to the pig urinary bladder neck

AIMS

The involvement of endothelin receptors in the contraction of the lower urinary tract smooth muscle is well established. There is scarce information, however, about endothelin receptors mediating relaxation of the bladder outlet region. The current study investigates the possible existence of endothelin ET(B) receptors involved in the relaxation of pig bladder neck.

METHODS

ET(B) receptor expression was determined by immunohistochemistry and urothelium-denuded bladder neck strips were mounted in organ baths for isometric force recording.

RESULTS

ET(B) -immunoreactivity (ET(B) -IR) was observed within nerve fibers among smooth muscle bundles and urothelium. BQ3020 (0.01-300 nM), an ET(B) receptor agonist, produced concentration-dependent relaxations which were reduced by BQ788, an ET(B) receptor antagonist, and by inhibitors of protein kinase A (PKA) and large (BK(Ca) )- or small (SK(Ca) )-conductance Ca(2+) -activated K(+) channels. Pretreatment with BK(Ca) or SK(Ca) channel inhibitors plus PKA blocking did not cause further inhibition compared with that exerted by inhibiting BK(Ca) or SK(Ca) channels only. BQ3020-induced relaxation was not modified by blockade of either nitric oxide (NO) synthase, guanylyl cyclase, cyclooxygenase (COX) or of intermediate-conductance Ca(2+) -activated-(IK(Ca) ), ATP-dependent-(K(ATP) ), or voltage-gated-(K(v) ) K(+) channels. Under non-adrenergic non-cholinergic (NANC) conditions, electrical field stimulation (0.5-16 Hz) evoked frequency-dependent relaxations, which were reduced by BQ788 and potentiated by threshold concentrations of BQ3020.

CONCLUSIONS

These results suggest that BQ3020 produces relaxation of the pig bladder neck via activation of muscle endothelin ET(B) receptors, NO/cGMP- and COX-independent-, cAMP-PKA pathway-dependent-mechanisms, and involving BK(Ca) and SK(Ca) channel activation. ET(B) receptors are also involved in the NANC inhibitory neurotransmission.

Role of calcitonin gene-related peptide in inhibitory neurotransmission to the pig bladder neck

PURPOSE

We studied the role of calcitonin gene-related peptide in nonadrenergic, noncholinergic neurotransmission to the pig bladder neck.

MATERIALS AND METHODS

We used immunohistochemical techniques to determine the distribution of calcitonin gene-related peptide immunoreactive fibers as well as organ baths for isometric force recording. We investigated relaxation due to endogenously released or exogenously applied calcitonin gene-related peptide in urothelium denuded phenylephrine precontracted strips treated with guanethidine, atropine and NG-nitro-L-arginine to block noradrenergic neurotransmission, muscarinic receptors and nitric oxide synthase, respectively.

RESULTS

Rich calcitonin gene-related peptide immunoreactive innervation was found penetrating through the adventitia and distributed in the suburothelial and muscle layers. Numerous, variable size, varicose calcitonin gene-related peptide immunopositive terminals were seen close below the urothelium. In the muscle layer calcitonin gene-related peptide immunopositive nerves usually appeared as varicose terminals running along muscle fibers. Electrical field stimulation (2 to 16 Hz) and exogenous calcitonin gene-related peptide (0.1 nM to 0.3 μM) evoked frequency and concentration dependent relaxation, respectively. Nerve responses were potentiated by capsaicin, decreased by calcitonin gene-related peptide (8-37) and abolished by tetrodotoxin, capsaicin sensitive primary afferent blockers, calcitonin gene-related peptide receptors and neuronal voltage gated Na+ channels. Calcitonin gene-related peptide-induced relaxation was potentiated by the neuronal voltage gated Ca2+ channels blocker ω-conotoxin-GVIA and decreased by calcitonin gene-related peptide (8-37). Calcitonin gene-related peptide relaxation was not modified by blockade of endopeptidases, nitric oxide synthase, guanylyl cyclase and cyclooxygenase.

CONCLUSIONS

Results suggest that calcitonin gene-related peptide is involved in the nonadrenergic, noncholinergic inhibitory neurotransmission of the pig bladder neck, producing relaxation through neuronal and muscle calcitonin gene-related peptide receptors. Nitric oxide/cyclic guanosine monophosphate and cyclooxygenase pathways do not seem to be involved in such responses.