Brief structural insight into the allosteric gating mechanism of BK (Slo1) channel

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Antiarrhythmic and Inotropic Effects of Selective Na+/Ca2+ Exchanger Inhibition: What Can We Learn from the Pharmacological Studies?

Life-long stable heart function requires a critical balance of intracellular Ca2+. Several ion channels and pumps cooperate in a complex machinery that controls the influx, release, and efflux of Ca2+. Probably one of the most interesting and most complex players of this crosstalk is the Na+/Ca2+ exchanger, which represents the main Ca2+ efflux mechanism; however, under some circumstances, it can also bring Ca2+ into the cell. Therefore, the inhibition of the Na+/Ca2+ exchanger has emerged as one of the most promising possible pharmacological targets to increase Ca2+ levels, to decrease arrhythmogenic depolarizations, and to reduce excessive Ca2+ influx. In line with this, as a response to increasing demand, several more or less selective Na+/Ca2+ exchanger inhibitor compounds have been developed. In the past 20 years, several results have been published regarding the effect of Na+/Ca2+ exchanger inhibition under various circumstances, e.g., species, inhibitor compounds, and experimental conditions; however, the results are often controversial. Does selective Na+/Ca2+ exchanger inhibition have any future in clinical pharmacological practice? In this review, the experimental results of Na+/Ca2+ exchanger inhibition are summarized focusing on the data obtained by novel highly selective inhibitors

Effect of thymol on kinetic properties of Ca and K currents in rat skeletal muscle

BACKGROUND: Thymol is widely used as a general antiseptic and antioxidant compound in the medical practice and industry, and also as a stabilizer to several therapeutic agents, including halothane. Thus intoxication with thymol may occur in case of ingestion or improper anesthesia. In the present study, therefore, concentration-dependent effects of thymol (30–600 micro-grams) were studied on calcium and potassium currents in enzymatically isolated rat skeletal muscle fibers using the double vaseline gap voltage clamp technique. RESULTS: Thymol suppressed both Ca and K currents in a concentration-dependent manner, the EC(50 )values were 193 ± 26 and 93 ± 11 μM, with Hill coefficients of 2.52 ± 0.29 and 1.51 ± 0.18, respectively. Thymol had a biphasic effect on Ca current kinetics: time to peak current and the time constant for inactivation increased at lower (100–200 μM) but decreased below their control values at higher (600 μM) concentrations. Inactivation of K current was also significantly accelerated by thymol (200–300 μM). These effects of thymol developed rapidly and were partially reversible. In spite of the marked effects on the time-dependent properties, thymol caused no change in the current-voltage relationship of Ca and K peak currents. CONCLUSIONS: Present results revealed marked suppression of Ca and K currents in skeletal muscle, similar to results obtained previously in cardiac cells. Furthermore, it is possible that part of the suppressive effects of halothane on Ca and K currents, observed experimentally, may be attributed to the concomitant presence of thymol in the superfusate

The myosin activator omecamtiv mecarbil: a promising new inotropic agent

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Can the electrophysiological action of rosiglitazone explain its cardiac side effects?

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Utódepolarizációk ionmechanizmusainak vizsgálata akciós potenciál clamp módszerrel = Afterdepolarization, Cellular electrophysiology, Action Potential Clamp

A project célja az volt, hogy megismerjük az utódepolarizációk által kiváltott ritmuszavarok hátterében álló ionmechanizmusokat. Hagyományos- és akciós potenciál feszültség clamp technika segítségével tanulmányoztuk az akciós potenciál alatt folyó ionáramok tulajdonságait emlős miocardiumban. Matematikai modellek alkalmazásával a tanulmányozott ionáramok viselkedése az akciós potenciál formájából prediktálható volt. - Vizualizáltuk és analizáltuk az akciós potenciál alatti lefutását a következő áramoknak: klorid áram, L-tipusú kalcium áram és a késői egyenirányító kálium áram lassú komponense. A klorid áram az akciós potenciál korai fázisában kifelé irányul, majd irányt vált. Gátlása az akciós potenciált nyújtja és fokozza az utódepolarizációk jelentkezésének gyakoriságát. Az L-tipusú kalcium áram az akciós potenciál első 20 milliszekunduma alatt eléri maximumát, majd platófázis nélkül igen gyorsan lecseng. Megfigyelésünk szerint a késői egyenirányító kálium áram lassú komponense a terminális repolarizáció igen fontos tényezője. - Vizsgáltuk az emlős szívizomzat ioncsatornáinak aszimmetrikus megoszlását. Összehasonlítottuk az ionáramokat és az akciós potenciál morfológiáját az szivizomzat különböző régióiban. Azt találtuk, hogy a tranziens outward K+ áram és a késői egyenirányító K+ áram lassú komponense jelentősen nagyobb az epicardiumban mint a midmyocardiumban mind humán mind kutya szívizom esetén. A Kv4.3, Kv1.4, KchIP2 és KvLQT1 csatornaproteinek expressziója ugyancsak jelentősen magasabb volt az epicardiumban. | The goal of this project was to obtain information on the ionic mechanism of cardiac arrhythmias caused different types of afterdepolarizations. We used traditional and action potential voltage clamp methods to understand the behavior of ionic currents during the action potential in mammalian myocardium. Using mathematical models we could predict the profile of ionic currents studied from the contour of action potential. - We visualized and analyzed the profile of the chloride current, the L-type calcium current and the slow component of delayed rectifier potassium current during the action potential. The chloride current showed an outward peak during the early phase of action potential, but later it became inward. Inhibition of the chloride current prolonged the action potential and facilitated the development of afterdepolarizations. The L-type calcium current showed an early peak during the firs 20 milliseconds of the action potential and decayed quickly without a plateau phase. The slow component of the delayed rectifier potassium current was found to be a crucial component of terminal repolarization. - We studied the asymmetrical distribution of ion channels in mammalian myocardium. We compared the ionic currents and the morphology of action potential in the different regions of the myocardium. We found that the amplitude of the transien outward K+ current and the slow componenet of the delayed rectifier K+ current was significanly larger in epicardiac than in midmyocardiac cells in both human and canine heart. Expression of Kv4.3, Kv1.4, KchIP2 and KvLQT1 was singificantly higher in epicardium

Perspectives of a myosin motor activator agent with increased selectivity

Clinical treatment of heart failure is still not fully solved. A novel class of agents, the myosin motor activators, acts directly on cardiac myosin resulting in an increased force generation and prolongation of contraction. Omecamtiv mecarbil, the lead molecule of this group, is now in human 3 phase displaying promising clinical performance. However, omecamtiv mecarbil is not selective to myosin, since it readily binds to and activates cardiac ryanodine receptors (RyR-2), an effect that may cause complications is case of overdose. In this study, in silico analysis was performed to investigate the docking of omecamtiv mecarbil and other structural analogues to cardiac myosin heavy chain and RyR-2 in order to select the structure which has a higher selectivity to myosin over RyR-2. In silico docking studies revealed that omecamtiv mecarbil has comparable affinity to myosin and RyR-2: the respective Kd values are 0.60 and 0.87 µM. Another compound CK-1032100 has much lower affinity to RyR-2 than omecamtiv mecarbil, while it still has a moderate affinity to myosin. It was concluded that further research starting from the chemical structure of CK-1032100 may result a better myosin activator burdened probably less by the RyR-2 binding side effect. It also is possible, however, that the selectivity of omecamtiv mecarbil to myosin over RyR-2 cannot be substantially improved, because similar moieties seem to be responsible for the high affinity to both myosin and RyR-2

Interactions of Cisplatin and Daunorubicin at the chromatin level

Unexpectedly, the widely used anticancer agents Cisplatin (Cis-Pt) and Daunorubicin (Dauno) exhibited cell type- and concentration-dependent synergy or antagonism in vitro. We attempted to interpret these effects in terms of the changes elicited by the drugs in the chromatin, the target held primarily responsible for the cytotoxicity of both agents. We measured the effect of Cis-Pt on the levels of Dauno in different cell compartments, the effect of Cis-Pt on Dauno-induced nucleosome eviction, and assessed the influence of Dauno on DNA platination in flow- and laser scanning cytometry as well as in laser ablation-inductively coupled plasma-mass spectrometry assays. We show that the two drugs antagonize each other through a decrease of interstrand crosslinks upon co-treatment with Dauno, and also via the diminished Dauno uptake in the presence of Cis-Pt, and both effects are observed already at low Dauno concentrations. At high Dauno concentrations synergy becomes dominant because histone eviction by Dauno intercalation into the DNA is enhanced in the presence of co-treatment with Cis-Pt. These interactions may have an impact on the efficacy of combination treatment protocols, considering the long retention time of DNA adducts formed by both agents

Diabetes mellitus attenuates the repolarization reserve in mammalian heart

Objective: In diabetes mellitus several cardiac electrophysiological parameters are known to be affected. In rodent experimental diabetes models changes in these parameters were reported, but no such data are available in other mammalian species including the dog. The present study was designed to analyse the effects of experimental type I diabetes on ventricular repolarization and its underlying transmembrane ionic currents and channel proteins in canine hearts. Methods and results: Diabetes was induced by a single injection of alloxan, a subgroup of dogs received insulin substitution. After the development of diabetes (8 weeks) electrophysiological studies were performed using conventional microelectrodes, whole cell voltage clamp, and ECG. Expression of ion channel proteins was evaluated by Western blotting. The QT(c) interval and the ventricular action potential duration in diabetic dogs Were moderately prolonged. This was accompanied by significant reduction in the density of the transient outward K+ current (I-to) and the slow delayed rectifier K+ current (I-Ks), to 54.6% and 69.3% of control, respectively. No differences were observed in the density of the inward rectifier K+ current (I-K1), rapid delayed rectifier K+ current (I-Kr), and L-type Ca2+ current (I-Ca). Western blot analysis revealed a reduced expression of Kv4.3 and MinK (to 25 +/- 21% and 48 +/- 15% of control, respectively) in diabetic dogs, while other channel proteins were unchanged (HERG, MiRP1, alpha(1c)) or increased (Kv1.4, KChIP2, KvLQT1). Insulin substitution fully prevented the diabetes-induced changes in I-Ks, KvLQT1 and MinK, however, the changes in I-to, Kv4.3, and Kv1.4 were only partially diminished by insulin. Conclusion: It is concluded that type I diabetes mellitus, although only moderately, lengthens ventricular repolarization, attenuates the repolarization reserve by decreasing I-to and I-Ks currents, and thereby may markedly enhance the risk of sudden cardiac death