ISSN 1990-7478, Biochemistry (Moscow) Supplement Series A: Membrane and Cell Biology, 2013, Vol. 7, No. 1, pp. 52–57. © Pleiades Publishing, Ltd., 2013. Original Russian Text © N.N. Khaertdinov, D.R. Ahmetshina, A.L. Zefirov, G.F. Sitdikova, 2012, published in Biologicheskie Membrany, 2012, Vol. 29, No. 4, pp. 231–237. 52 Hydrogen sulfide (H 2 S) is known for a long time as a toxic gas [1]; however, more and more data show that H 2 S is synthesized endogenously and has various physiological effects on the cardiovascular and ner- vous systems, as well as on gastrointestinal tract [2–7]. It is supposed that H 2 S is an endogenous “gasotrans- mitter”, like two other physiologically active gasses: nitric oxide (NO) and carbon monoxide (CO) [8, 9]. In the cardiovascular system, H 2 S is synthesized from L-cysteine by cystathionin-γ-lyase and 3-mercapto- sulfotransferase [5, 10, 11], induces vasodilation and regulates proliferation, apoptosis, and angiogenesis. In addition, H 2 S has a cardioprotective effect against injuries induced by ischemia–reperfusion [5, 10, 12]. It is interesting that H 2 S influences the vascular tone of all classes of vertebrates (fish, amphibian, reptiles), including vasoconstriction and vasodilation, which indicates the phylogenetic antiquity of H 2 S as a gas- otransmitter and universality of its action [13, 14]. It was shown in the intact rat heart and isolated car- diomyocytes that H 2 S reduced the duration of action potential and had a negative inotropic effect [10, 15, 16]. The mechanisms of H 2 S action in mammalian myocardium include, according to different data and depending on animal species, the adenylate cyclase system, ATP-dependent K channels, and voltage- dependent L-type Ca channels [11, 15–17]. The reg- ulation of cAMP synthesis by H 2 S may play a critical role in cardioprotection, as there is a substantial decrease in H 2 S production in different models of ischemia and hyperstimulation of β-adrenoceptors [10, 12]. In the frog myocardium, the hydrogen sulfide donor NaHS had a dose-dependent negative inotropic effect [18], but the mechanisms of H 2 S action were not revealed. The goal of this work was to study the effects of exogenous and endogenous H 2 S on frog myocardial contractility and to elucidate the plausible molecular mechanisms of its action. MATERIALS AND METHODS The experiments on contractility recording were performed on the strips of frog myocardium in a Pow- Hydrogen Sulfide in Regulation of Frog Myocardium Contractility 1 N. N. Khaertdinov a , D. R. Ahmetshina a , A. L. Zefirov b , and G. F. Sitdikova a a Kazan Federal University, ul. Kremlevskaya 18, Kazan, 420008 Russia e-mail: Guzel.Sitdikova@ksu.ru b Kazan State Medical University, Ministry of Health and Social Development of the Russian Federation, ul. Butlerova, 42, Kazan, 420012 Russia Received June 25, 2011; in final form, October 19, 2011 Abstract—Hydrogen sulfide (H 2 S) is an endogenously synthesized gaseous molecule which, along with nitric oxide and carbon monoxide, induces a number of effects in cardiovascular system under normal and patho- logical conditions. In the present work, the effects and underlying mechanisms of the H 2 S donor sodium hydrosulfide (NaHS) on the isometric force of frog myocardium contraction have been studied. NaHS at the concentration of 100 μM induced negative inotropic effect and reduced the maximum velocity of te contrac- tion and relaxation of the isolated ventricle strips. The substrate of H 2 S synthesis, L-cysteine (200 μM and 1 mM), induced the same effect, while the inhibitors of cystathionin-γ-lyase, the H 2 S-producing enzyme in heart, β-cyanoalanine (500 μM) and propargylglycine (500 μM), increased the amplitude of contraction. Inhibition of cystathionin-γ-lyase by β-cyanoalanine prevented the negative inotropic effect of L-cysteine. After the inhibition of adenylate cyclase by MDL-12,330A (3 μM) or phosphodiesterases by IBMX (200 μM), the effect of NaHS was less than that in the control. In the presence of membrane-penetrating analogous of cAMP, 8Br- cAMP (100 μM) and pCPT-cAMP (100 μM), the negative inotropic effect of NaHS was completely retained. The effect of NaHS significantly decreased after preliminary application of the NO donor, SNAP (10 μM), and did not change after the inhibition of NO synthases by L-NAME (100 μM). The results suggest the possibility of endogenous synthesis of H 2 S in frog myocardium and regulation of its contractility by the activation of phosphodiesterases hydrolyzing cAMP, which leads to a decrease in the activation of cAMP- dependent protein kinases and phosphorylation of voltage-dependent L-type Ca channels. As a result, the reduction of calcium entry into cardiomyocytes decreases the contractility of frog myocardium. Keywords: hydrogen sulfide, myocardial contractility, adenylate cyclase, nitric oxide DOI: 10.1134/S1990747812030117 ARTICLES 1 The article was translated by the authors.