The role of L-cysteine/hydrogen sulfide pathway on beta-3 adrenoceptor induced relaxation in mouse gastric fundus

In our study, the possible role of the L-cysteine/hydrogen sulfide pathway in Beta-3 Adrenoceptor (β3–AR) mediated relaxation in isolated mouse gastric fundus tissue was investigated. For this purpose, the non-selective β-AR agonist isoprenaline (10-9-10-4 M) and the selective β3-AR agonist BRL 37344 (10-9-10-4 M), L-cysteine (endogenous H2S; 10-6-10-2 M) and sodium hydrogen sulfide (NaHS) (exogenous H2S; 10-6-10-3 M) were used in carbachol (10-6 M) pre-contracted mouse gastric fundus. Firstly, the non-selective β-AR antagonist propranolol (10-6 M) reduced the relaxant response obtained with isoprenaline; but it did not cause a change in the relaxant response obtained with BRL 37344. On the other hand, the selective β3–AR antagonist SR 59230A (10-5 M) inhibited the relaxant responses obtained with BRL 37344. In addition, L-cysteine and NaHS relaxations were obtained in the tissue. The effects of endogenous H2S synthesis inhibitors propargylglycine (PAG; cystathionine-gamma-lyase (CSE) inhibitor; 10–2 M), aminooxyacetic acid (AOAA; cystathionine-β-synthase (CBS) inhibitor; 10–2 M); seperately or their combination, on the relaxant response to L-cysteine and BRL 37344 were investigated. PAG, AOAA and the combination of these inhibitors significantly reduced the relaxant responses induced by L-cysteine and BRL 37344. Endogenous H2S levels measured in the tissue also support these findings. Basal H2S release was detected in the measurements; H2S level increased in the presence of NaHS, L-cysteine and BRL 37344. High H2S level in L-cysteine and BRL 37344 groups decreased significantly with PAG and AOAA enzyme inhibitors. In addition, protein expressions of CSE, CBS and 3-mercaptopurivate sulfurransferase (3-MST) enzymes responsible for endogenous H2S synthesis and β3-ARs were demonstrated by western blot method. As a result, it has been shown that endogenous H2S in mouse gastric fundus tissue is synthesized from L-cysteine by means of CSE and CBS enzymes, that there are β3-adrenoceptors in this tissue and L-cysteine/hydrogen sulfide pathway plays a role in β3-AR mediated relaxation.