a b s t r a c tThis minireview focuses on observation of the properties, functional significance, and modulation of single chloride channels in the mitochondrial inner membrane using two electrophysiological methods -the patch-clamp and bilayer lipid membrane methods. Measurements of parameters such as conductance, Cl À /K + selectivity, voltage or pH dependence as well as their modulation by endogenous and exogenous compounds using individual mitochondrial chloride channels result in an unexpectedly wide range of values. This paper discusses the origin of this wide variety of channel parameters and the possible involvement of these channels in mitochondrial membrane potential oscillations, apoptosis, carrier function, and mitochondrial fusion and fission.

H2S donor molecules have the potential to be viable therapeutic agents. The aim of this current study was (i) to investigate the effects of a novel triphenylphosphonium derivatised dithiolethione (AP39), in the presence and absence of reduced nitric oxide bioavailability and (ii) to determine the effects of AP39 on myocardial membrane channels; CaV3, RyR2 and Cl(-). Normotensive, L-NAME- or phenylephrine-treated rats were administered Na2S, AP39 or control compounds (AP219 and ADT-OH) (0.25-1 µmol kg(-1)i.v.) and haemodynamic parameters measured. The involvement of membrane channels T-type Ca(2+) channels CaV3.1, CaV3.2 and CaV3.3 as well as Ca(2+) ryanodine (RyR2) and Cl(-) single channels derived from rat heart sarcoplasmic reticulum were also investigated. In anaesthetised Wistar rats, AP39 (0.25-1 µmol kg(-1) i.v) transiently decreased blood pressure, heart rate and pulse wave velocity, whereas AP219 and ADT-OH and Na2S had no significant effect. In L-NAME treated rats, AP39 significantly lowered systolic blood pressure for a prolonged period, decreased heart rate and arterial stiffness. In electrophysiological studies, AP39 significantly inhibited Ca(2+) current through all three CaV3 channels. AP39 decreased RyR2 channels activity and increased conductance and mean open time of Cl(-) channels. This study suggests that AP39 may offer a novel therapeutic opportunity in conditions whereby (•)NO and H2S bioavailability are deficient such as hypertension, and that CaV3, RyR2 and Cl(-) cardiac membrane channels might be involved in its biological actions.

Abstract. As a part of the nitroso signalling pathway, nitroso-compounds serve as stores and carriers of NO; as part of the sulphide signalling pathway, bound sulfane-sulphur compounds serve as stores and carriers of H 2 S. Here we hypothesise a coupled sulphide-nitroso signalling pathway, in which H 2 S plays a main role. H 2 S releases NO from the endogenous S-nitroso-compounds nitrosocysteine, nitroso-acetylcysteine and nitroso-albumin. Relaxation of noradrenaline-precontracted aortic rings by H 2 S is also enhanced in the presence of nitroso-albumin, which may implicate the involvement of the nitroso signalling pathway. Pretreatment of albumin, cysteine, N-acetylcysteine and lipids with H 2 S results in binding of sulphur to these compounds creating thus new-modified sulphur compounds that release NO from nitroso-compounds directly and/or through released H 2 S, which suggests sulphide-nitroso signalling pathway participation. This hypothesis is supported by the observation that the pretreatment of noradrenaline-precontracted aortic rings with H 2 S significantly enhanced relaxation induced by nitroso-glutathione in the absence of H 2 S. We assume that the NO release from nitroso-compounds directly by H 2 S or indirectly by the H 2 S-induced sulphur-bound compounds represents coupled sulphide-nitroso signalling, which may explain some of the numerous biological effects of H 2 S that are shared with NO.

Physiological and pathological functions of mitochondria are highly dependent on the properties and regulation of mitochondrial ion channels. There is still no clear understanding of the molecular identity, regulation, and properties of anion mitochondrial channels. The inner membrane anion channel (IMAC) was assumed to be equivalent to mitochondrial centum picosiemens (mCS). However, the different properties of IMAC and mCS channels challenges this opinion. In our study, we characterized the single-channel anion selectivity and pH regulation of chloride channels from purified cardiac mitochondria. We observed that channel conductance decreased in the order: Cl⁻ > Br⁻ > I⁻ > chlorate ≈ formate > acetate, and that gluconate did not permeate under control conditions. The selectivity sequence was Br⁻ ≥ chlorate ≥ I⁻ ≥ Cl⁻ ≥ formate ≈ acetate. Measurement of the concentration dependence of chloride conductance revealed altered channel gating kinetics, which was demonstrated by prolonged mean open time value with increasing chloride concentration. The observed mitochondrial chloride channels were in many respects similar to those of mCS, but not those of IMAC. Surprisingly, we observed that acidic pH increased channel conductance and that an increase of pH from 7.4 to 8.5 reduced it. The gluconate current appeared and gradually increased when pH decreased from pH 7.0 to 5.6. Our results indicate that pH regulates the channel pore diameter in such a way that dilation increases with more acidic pH. We assume this newly observed pH-dependent anion channel property may be involved in pH regulation of anion distribution in different mitochondrial compartments.

The objective of this work was to characterize in more detail the inhibition effect of diisothiocyanatostilbene-2',2-disulfonic acid (DIDS) on anion channels isolated from the rat heart mitochondria. The channels reconstituted into a planar lipid membrane displayed limited powers of discrimination between anions and cations and the ion conductance measured under asymmetric (250/50 mM KCl, cis/trans) and symmetric (150 mM KCl) conditions was approximately 100 pS. DIDS caused a dramatic decrease in the channel activity (IC(50) = 11.7 +/- 3.1 microM) only when it was added to the cis side of a planar lipid membrane. The inhibition was accompanied by the significant prolongation of closings and the shortening of openings within the burst as well as gaps between bursts were prolonged and durations of bursts were reduced. The blockade was complete and irreversible when concentration of DIDS was increased up to 200 microM. Our data indicate that DIDS is an allosteric blocker of mitochondrial anion channels and this specific effect could be used as a tool for reliable identification of anion channels on the functional level.

Abstract.We studied the involvement of O 2 , pH and low molecular thiols in H 2 S-induced decomposition of S-nitrosoglutathione (GSNO). The GSNO decomposition -• NO release was evaluated by UV-VIS spectroscopy and Griess assay. The H 2 S donor Na 2 S was used. O 2 slightly increased, but was not necessary for the H 2 S-induced GSNO decomposition. The rate of GSNO decomposition depended on pH; the maximum rate was observed at pH 7.4-8.0, and this decreased with lowering pH (6.4-4.5) as well as with increasing pH at 9.0-12.0. H 2 S-induced GSNO decomposition was slowed by the presence of other thiols, such as L-cysteine (Cys), N-acetyl-L-cysteine (NAC) and Lglutathione (GSH), but not in the presence of L-methionine (Met) or oxidized glutathione (GSSG). In sharp contrast, at pH 6.0, H 2 S-induced GSNO decomposition was negligible, yet the presence of Cys, NAC and GSH induced the H 2 S-driven GSNO decomposition (whilst Met and GSSG were inactive). In conclusion we postulate an involvement of low molecular thiols and pH in• NO signaling, by modulating the interactions of H 2 S with nitroso compounds, and hence in part they also appear to control H 2 S-triggered• NO release. The interaction of H 2 S and/or its derivatives with the thiol group may be responsible for the observed effects.

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