Chloride channels and Na2S‐induced relaxation

Ana Mijušković, Aleksandra Nikolić Kokić, Zorana Oreščanin Dušić, Marija Slavić, Mihajlo B Spasić, Duško Blagojević

Hydrogen sulphide reduces uterine contractility and is of potential interest to treat uterine disorders.The aim of this study was to explore the mechanism of sodium sulphide (Na2 S)-induced relaxation of rat uterus, investigating importance of redox effects and ion channel-mediated mechanisms, as well as interactions between these two mechanisms. Organ bath studies were employed to perform pharmacological assessment of Na2 S effects by using uterine strips that were exposed to Na2 S with or without: Cl(-) channel blockers (DIDS, NFA, IAA-94, T16Ainh-A01, TA), raised KCl (15 mM and 75mM), K(+) channel inhibitors (glibenclamide, TEA, 4-AP), L-type Ca(2+) channel activator (S-Bay K 8644), propranolol and methylene blue. Antioxidative enzyme activities were measured in homogenates of treated uteri. Expression studies of the bestrophin channel 1 (BEST-1) were performed by Western blotting and RT-PCR. Na2 S caused concentration-dependent reversible relaxation of spontaneously active and calcium-induced uteri, affecting both amplitude and frequency of contractions. Uteri exposed to 75 mM KCl were less sensitive to Na2 S compared to uteri under 15mM KCl. DIDS abolished Na2 S-induced relaxation. Relaxation was not affected by other modulators, or by the absence of extracellular HCO3 (-) suggesting involvement of chloride ion channel. Na2 S in combination with different modulators provoked specific changes in anti-oxidative profiles of uteri. Expression studies demonstrated presence of BEST-1 in rat uterus at both the mRNA and protein level. These data demonstrate that Na2 S relaxatory effects are mediated mainly via DIDS-sensitive Cl(-) -pathway. Components of relaxation are redox and Ca(2+) dependent.