Role of H2S in Regulation of Vascular Tone in Metabolic Disorders.

We studied the effect of the H2S donor (NaHS, 1-500 µM) on the contractile responses of isolated aortic smooth muscle segments from rats with metabolic syndrome induced by high-fat, high-carbohydrate diet. It was found that the vasorelaxing effect of NaHS (5-100 µM) decreased in under conditions of MS. The endothelial NO synthase inhibitor L-NAME (100 µM) suppressed the effect of NaHS, while cystathionine-gamma-lyase inhibitor PAG (100 µM) decreased the vasodilating effects of acetylcholine (0.1-100 µM). Application of endogenous NO precursor L-arginine (1 mM) potentiated in the effects of H2S donor NaHS. Thus, the contractile activity of vascular smooth muscles in metabolic syndrome is determined by not only the effect of H2S, but also the influence of NO.

Regulation of Vascular Smooth Muscle Contractions in the Model of Metabolic Syndrome.

Reduced glucose tolerance, hyperglycemia, and imbalance in lipid levels were found in rats with metabolic syndrome induced by a high-fat, high-carbohydrate diet. The contractile responses of intact and endothelium-denuded aortic smooth muscle segments from rats with metabolic syndrome to application of acetylcholine, phenylephrine, sodium nitroprusside, and forskolin were studied by mechanographic method. It was found that endothelial dysfunction develops against the background of metabolic and hemodynamic disorders in metabolic syndrome. It was shown that the regulation of vasoconstrictor reactions of vascular smooth muscles in metabolic syndrome is due to a decrease in Ca2+ entry, mainly voltage-independent, as well as changes in the function of cGMP- and cAMP-activated K+-channels.

H2S-Mediated Changes in Erythrocyte Volume: Role of Gardos Channels, Na+,K+,2Cl- Cotransport and Anion Exchanger.

The effect of H2S on changes in erythrocyte volume was studied by spectrophotometrical and potentiometric methods. It was found that H2S donor NaHS (2.5, 10, and 100 µM) induced an increase in erythrocyte volume in heterosmotic media. Activation of Gardos channels with A23187 or ascorbate-phenazine methosulfate system causes erythrocyte shrinkage and hyperpolarization of their membrane, while addition of NaHS restored erythrocyte volume. The decrease in erythrocyte volume upon blockade of Na+,K+,2Cl- cotransporter (bumetanide) or anion exchanger (SITS) was abolished by H2S donor NaHS, which attested to an important role of these transporters and chlorine conductivity of the membrane in the maintenance of the homeostasis of blood cells.

Role of Carbon Monoxide in the Mechanisms of Action of Extracellular ATP on Contractile Activity of Vascular Smooth Muscle Cells.

We studied the role of carbon monoxide (CO) in the effect of P2X and P2Y receptor agonist ATP on the tone of rat aorta segments with intact endothelium. ATP (1-1000 µM) and P2X receptor agonist α,ß-MeATP (100 µM) relaxed segments precontracted with phenylephrine (10 µM), while UTP (100-1000 µM) increased the amplitude of phenylephrine-induced contraction. The relaxing effect of ATP was enhanced by CORM II (100 µM), NO synthase inhibitor L-NAME, and guanylate cyclase inhibitor ODQ and attenuated by ZnPP IX (100 µM). The constrictive effect of UTP was weakened by CORM II (100 µM), but was not changed by ZnPP IX (100 µM). ZnPP IX (100 µM) weakened the relaxation response to α,ß-MeATP. Thus, ATP involves the CO-dependent signaling cascade through P2X receptors.

Molecular Mechanisms of Action of Gas Transmitters NO, CO and H2S in Smooth Muscle Cells and Effect of NO-generating Compounds (Nitrates and Nitrites) on Average Life Expectancy.

Gaseous signaling molecules (gas transmitters) take an especial position among the numerous signaling molecules involved in the regulation of both intracellular processes that occur in different types of cells and cell-cell interactions. At present time, gas transmitters include three molecules whose enzymatic systems of synthesis and degradation, physiological action and intracellular effectors, the change of which under the action of gas transmitters may result in physiological and/or pathophysiological effects are well- determined. These molecules include nitrogen oxide (NO), carbon monoxide (CO) and hydrogen sulfide (H2S). They are involved in the regulation of functions of various organs and systems of the human body, including the circulatory system. Interaction of NO, CO and H2S with various enzymatic and structural components of endothelial and, especially, smooth muscle cells has a significant impact on vascular tone and blood pressure. Furthermore, the crossing of NO-, CO- and H2S-mediated signaling pathways at common effectors and interaction with each other can determine the end, resulting functional response of the cell. The knowledge of the molecular targets of gas transmitters' action, the structure of the binding centers for gas transmitters and their interaction with each other may be essential in the development of methods of regulation of these signaling systems by targeted, directed action. This review summarizes the molecular mechanisms of the NO, CO and H2S interaction with the main targets, which carry out their regulatory effect on vascular smooth muscle cells. Also we describe here different ways of cross-regulation of NO-, CO- and H2S-dependent signaling pathways. We analyzed NO-synthase and nitrite reductase systems of nitric oxide cycle and discuss the nitrate-nitrite background of the existence of modern man, which can substantially modify the signaling system, the metabolism of virtually all cell ultrastructure of neurons, neuron-neuron and neuron-glial interactions and exerts its influence on socially significant diseases that can affect the quality and the average life expectancy.

Regulation of Contractile Responses of Vascular Smooth Muscle Cells under Conditions of Hypoxia-Reoxygenation.

We analyzed the effects of hypoxia and reoxygenation on changes in contractile activity in rat aortic smooth muscles. Both hypoxia and reoxygenation induced relaxation of smooth muscle cells precontracted with high-potassium Krebs solution (30 mM KCl) or α1-adrenoceptor agonist phenylephrine. Vasodilation resulted from enhancement of potassium permeability of smooth muscle cell membranes caused by activation of voltage-gated potassium channels (triggered by both precontracting agents) or by opening of ATP-sensitive potassium channels (phenylephrine). In isolated smooth muscle cells, both hypoxia and inhibition of Na+,K+-ATPase with ouabain led to depletion of intracellular store of macroergic substances, reduced potassium concentration, and elevated the content of sodium ions.

[THE ROLE OF HYDROGEN SULFIDE IN VOLUME-DEPENDENT MECHANISMS OF REGULATION OF VASCULAR SMOOTH MUSCLE CELLS CONTRACTILE ACTIVITY].

The hydrogen sulfide (H2S) influence on the contractile activity of vascular smooth muscle cells (SMC) was studied on endothelium-denuded aortic ring segments of male Wistar rats with method of mechanography. Contractions of SMS were induced by incubation in high potassium solution as well as in hyper-, hypo- and isosmotic solutions. 5-100 LM of H2S donor--sodium hydrosulfide (NaHS) increased mechanical tension of SMC precontracted with high potassium solution that was abolished by bumetanide--the inhibitor of Na+, K+, 2Cl(-) -cotransporter (NKCC), but 100-1000 microM of NaHS relaxed SMS. NaHS (10 microM) increased the amplitude of hyper- and isosmotic contraction, but not of hyposmotic contraction. NaHS (ImM) decreased the amplitude of hyper-, iso-, and hyposmotic contractions. The direct measurements of NKCC activity with radionuclide method showed an increase in NKCC activity under the action of 5-100 microM of NaHS. These findings suggest that low concentrations of H2S participate in the NKCC activation. This mechanism underlines constrictive action of H2S on smooth muscle cells.

[Gas Signalling in Mammalian Cells].

At the end of the last century after the discovery of signaling functions of nitric oxide (NO, II), a new class of biologically active substances was admitted. It includes so-called gas transmitters acting as intercellular and intracellular regulators of different physiological functions. Currently, this class includes such gases as NO, carbon monoxide (CO) and hydrogen sulfide (H2S). It was found that these gases regulate not only functions of the. gastrointestinal tract and the cardiovascular system, where it has been determined initially, but also affect the function of the central and peripheral nervous.systems. Apparently, they constitute a single complex of gas transmitters, which easily penetrates through the membrane and regulates numerous enzymatic and non enzymatic cells reactions. This review presents the mechanisms of gas transmitters' influence on the electrical and contractile properties of smooth muscle cells (SMC) as a possible new ways to interact with the "classical" intracellular signaling cascades (Ca2+, cyclic nucleotides) and effectors systems. On account of their interactions the role of cyclic nucleotides and calcium ions in the implementation of the signal gas molecules functions is analyzed. We summarize the literature data and the results of our own research on the role of SMC membrane ion-transporting systems in myogenic effects of NO, CO and H2S and describe possible reasons of gas transmitters multidirectional influence on the excitation-contraction coupling in SMC.