400 ISSN 0022-0930, Journal of Evolutionary Biochemistry and Physiology, 2018, Vol. 54, No. 5, pp. 400—407. © Pleiades Publishing, Ltd., 2018. Original Russian Text © I.F. Shaidullov, M.U. Shafigullin, L.M. Gabitova, F.G. Sitdikov, A.L. Zefirov, G.F. Sitdikova, 2018, published in Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, 2018, Vol. 54, No. 5, pp. 355—361. COMPARATIVE AND ONTOGENIC PHYSIOLOGY Role of Potassium Channels in the Effects of Hydrogen Sulfide on Contractility of Gastric Smooth Muscle Cells in Rats I. F. Shaidullov a , M. U. Shafigullin a , L. M. Gabitova a , F. G. Sitdikov a , A. L. Zefirov b , and G. F. Sitdikova a * a Kazan Federal University, Kazan, Russia b Kazan State Medical University, Kazan, Russia *e-mail: sitdikovaguzel@gmail.com Received April 3, 2017 Abstract—The effect of sodium hydrosulfide (NaHS), a hydrogen sulfide (H 2 S) donor, on spontaneous contractile activity of rat gastric smooth muscle cells was analyzed. Experiments were conducted on gastric stripes under conditions of isometric contraction. It was shown that NaHS has a biphasic effect on spontaneous contractile activity, increasing tonic tension and the amplitude of phasic contractions within the first minutes since application. This initial phase is followed by a decrease in amplitude, basal tone, and frequency of spontaneous contractions. The inhibitory effect of NaHS was dose-dependent at concentrations from 10 to 600 μM. Preliminary application of tetraethylammonium and 4-aminopirydine, inhibitors of voltage-gated and calcium- activated potassium channels, prevented a NaHS-induced initial increase in basal tone and phasic contraction amplitude. Activation of ATP-dependent potassium channels (K ATP -channels) by diazoxide prevented in part a NaHS-induced decrease in basal tone and amplitude of spontaneous contractions. Glibenclamide, an inhibitor of K ATP -channels, decreased the inhibitory effect of NaHS on amplitude, basal tone and frequency of spontaneous contractions. It was concluded that in rat gastric smooth muscles the excitatory effect of H 2 S is mediated by the inhibition of voltage- gated and calcium-activated potassium channels, while its inhibitory effect involves the activation of K ATP -channels. DOI: 10.1134/S0022093018050083 Key words: rat gastric smooth muscle cells, hydrogen disulfide, contractility, voltage-gated and calcium-activated potassium channels, ATP-dependent potassium channels. as well as 3-mercaptopyruvate sulftransferase with a concomitant activation of cysteine aminotrans- ferase [3, 4]. Apart from endogenous production, an important source of H 2 S is represented by sulfate-reducing bacteria isolated from the hu- man gut and able to reduce sulfates contained in foods and intestinal secretions to sulfides, includ- ing H 2 S [3, 4]. In the gastrointestinal tract (GIT), CBS and CSE expression was found in varied cell INTRODUCTION Hydrogen sulfide (H 2 S) is a gaseous media- tor which, along with nitrogen oxide and carbon monoxide, influences various functions of the or- ganism under physiological and pathological con- ditions [1–6]. H 2 S is synthesized endogenously in different tissues by the enzymes cystathionine-β- synthase (CBS) and cystathionine-γ-lyase (CSE)