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The determination of chlorine dioxide using Naphthol Green was investigated in the presence of various chlorinated species that can occur under normal water treatment conditions. Ammonium sulfamate (0.75 mol L−1) was used as a masking agent. Naphthol Green selectively reacts with 0–13 mg L−1 ClO2 at pH 9, yielding a linear response (0.9991) with a limit detection of 0.1 mg L−1 ClO2. Several species, , , ClO−, and free available chlorine (FAC), were studied as potential interferents using this method. There was found to be less than 2% interference due to 85 mg L−1 FAC, 23 mg L−1 ClO− and excess of other oxychlorine species could be tolerated without interference.

Previous data have showed that application of ivabradine, a selective blocker of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, leaded to divergent trends regarding proarrhythmic and antiarrhythmic effects in atrial fibrillation (AF). The aim of this study was to investigate the

Myricetin (Myr) is a flavonoid that exerts anti-arrhythmic effects. However, its potential effects on ion channels have remained elusive. The aim of the present study was to investigate the effects of Myr on Kv1.5 channels in HEK293 cells. The current of Kv1.5 channels (Ikur) in HEK293 cells was recorded using the whole-cell patch-clamp technique and the expression of the Kv1.5 protein was measured using western blot analysis 24 h after treatment with Myr. The results showed that 5 µM Myr significantly reduced Ikur from 215.04 ± 40.59 to 77.72 ± 17.94 pA/pF (P

Adult mesenchymal stem cells (MSCs) hold great promise for the repair of heart defects. Both bone marrow-derived mesenchymal stem cells (BMSCs) and adipose tissue-derived stem cells (ASCs) are multipotent and may be induced by 5-azacytidine to differentiate into cardiomyocytes. However, the differentiation potential of human MSCs into sinus node-like cells has not been studied extensively. The aim of this study was to analyze the differences in proliferation and phenotype of ASCs and BMSCs from the same donors and to evaluate their capacity to differentiate into sinus node-like cells in vitro. Five passaged cells from bone marrow and adipose tissue were treated with 10 µM 5-azacytidine for 48 h and further cultured in complete medium for 4 weeks. A comparative study of cultured ASCs and BMSCs was carried out, and the morphological parameters, proliferative capacity, expression of surface markers and differentiation potential to sinus node-like cells were characterized. No morphologic differences were observed between ASCs and BMSCs. Flow cytometric analysis revealed that ASCs and BMSCs both expressed CD29, CD44, CD90 and CD105 and did not express CD34 and CD14, while CD49d, CD106 and CD34 were differentially expressed. Growth curves and doubling time determined with the Cell Counting Kit-8 (CCK-8) demonstrated that ASCs had a stronger proliferative ability than BMSCs. Histological immuofluorescence staining suggested that ASCs and BMSCs were capable of differentiating into sinus node-like cells and that the positive expression ratios of cTNI were higher in ASCs compared to BMSCs at 4 weeks. Expression of the HCN2 and HCN4 genes was detected by reverse transcriptase polymerase chain reaction, and the results revealed that the expression of the HCN genes appeared earlier in ASC-derived sinus node-like cells. ASCs expressed HCN2 and HCN4 shortly after induction with 5-azacytidine for 2 weeks, although BMSCs expressed these genes after 4 weeks. The expression levels of HCN2 and HCN4 mRNA in ASC-derived cells were higher compared to those of BMSCs at 4 weeks. In conclusion, ASCs may be a better candidate as a novel source of cell therapy in sinus bradycardia disorders than BMSCs.

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels underlie the pacemaker currents (I f ) in cardiac cells. The objectives of this study were to investigate the electropharmacological activity of amiodarone on human HCN channels heterologously expressed in Xenopus laevis oocytes. hHCN channels were expressed in oocytes and studied using the standard two-electrode voltage-clamp techniques. The results show that amiodarone blocks hHCN channels heterologously expressed in the Xenopus oocytes in a concentration- and use-dependent manner, but doesn't modify the voltage dependence of activation and reversal potentials. And the removal of blockage of HCN channels by amiodarone was favored by inward current flow, not by hyperpolarizing potential. Characteristics of blockage on hHCN channels were consistent with those of amiodarone as “trapped” drugs on human ether-a-go-go-related gene (HERG) channels. These results will be useful for elucidating the potentially antiarrhythmic mechanism of amiodarone.

BACKGROUND There is a clear association between excessive ethanol ( EtOH ) consumption and the risk of sudden cardiac death. The hyperpolarization-activated cyclic nucleotide-gated (HCN) current, I (f) , is known to contribute to spontaneous pacemaker activity of sinoatrial (SA) node cells. However, the exact mechanisms of EtOH on arrhythmia induction are not well understood. METHODS The preparations of SA node were excised from rabbit heart, transmembrane potentials were recorded by standard glass microelectrode technique, and a whole-cell patch clamp technique was used to record I (f) in enzymatically isolated rabbit SA node pacemaker cells. Human HCN2 (hHCN2) and HCN4 channels were heterologously expressed in Xenopus oocytes and studied using 2-electrode voltage clamp technique. RESULTS Superfusion of EtOH increased the spontaneous firing frequency of SA node cells in a reversible fashion. Treatment with ivabradine irreversibly depressed basal firing frequency and markedly attenuated the enhancement effect of EtOH on firing. The stimulatory effects of EtOH on I (f) were concentration-dependent in the range of 1 to 100 mM, with an average EC (50) value of 20.81 ± 6.71 mM and Hill coefficient of 1.19 ± 0.10. Furthermore, EtOH reversibly enhanced the HCN currents in a concentration-dependent fashion with an EC (50) value of 18.41 ± 2.75 mM for the HCN2 channel and 21.98 ± 3.54 mM for the HCN4 channel, which was accompanied by the acceleration of activation and deactivation kinetics. In addition, EtOH , at both moderate and high doses, caused a shift in the voltage dependence of hHCN4 channel activation to more depolarizing potentials. However, superfusion of high, not moderate, concentration of EtOH caused a shift in the voltage dependence of hHCN2 channel activation to more hyperpolarizing potentials. CONCLUSIONS This study provides insight into the molecular interaction of EtOH and the hHCN channels, which may shed light on elucidating the potentially proarrhythmic mechanism of EtOH .

Cardiac stem cells (CSCs) can differentiate into cardiac phenotypes representing early cardiomyocyte-like cells. However, CSCs-derived specification into sinus nodal cells is rarely known. Using the demethylating agent, 5-Aazacytidine (5-Aza), we tried to follow the process of cardiac specialization into sinus node-like cells. The c-kit+ cells were isolated from 1-month-old rat hearts and sorted by a flow cytometry cell sorting system. Then, analyses of immunofluorescence and reverse transcription polymerase chain reaction were performed on the cells. The sorted c-kit+ cell are self-renewing and clonogenic. Some of the c-kit+ cell could spontaneously express GATA-4, cardiac troponin I (cTnI), smooth muscle actin (SMA) and CD31. At week 8, the cells treated with 10 μM 5-Aza expressed GATA-4 and cTnI at rates of 31.4±2.6% and 32.6±8.5%. Correspondingly, the rates were 21.4±8.1% and 18.7±4.3% in the cells without 5-Aza. The difference of GATA-4 or cTnI expression rate between two groups was of significance respectively, P

To investigate the blocking effects of methylflavonolamine (MFA) on human Na(V)1.5 channels expressed in Xenopus laevis oocytes and on sodium currents (I(Na)) in rabbit ventricular myocytes.Human Na(V)1.5 channels were expressed in Xenopus oocytes and studied using the two-electrode voltage-clamp technique. I(Na) and action potentials in rabbit ventricular myocytes were studied using the whole-cell recording.MFA and lidocaine inhibited human Na(V)1.5 channels expressed in Xenopus oocytes in a positive rate-dependent and concentration-dependent manner, with IC(50) values of 72.61 micromol/L and 145.62 micromol/L, respectively. Both of them markedly shifted the steady-state activation curve of I(Na) toward more positive potentials, shifted the steady-state inactivation curve of I(Na) toward more negative potentials and postponed the recovery of the I(Na) inactivation state. In rabbit ventricular myocytes, MFA inhibited I(Na) with a shift in the steady-state inactivation curve toward more negative potentials, thereby postponing the recovery of the I(Na) inactivation state. This shift was in a positive rate-dependent manner. Under current-clamp mode, MAF significantly decreased action potential amplitude (APA) and maximal depolarization velocity (V(max)) and shortened action potential duration (APD), but did not alter the resting membrane potential (RMP). The demonstrated that the kinetics of sodium channel blockage by MFA resemble those of class I antiarrhythmic agents such as lidocaine.MFA protects the heart against arrhythmias by its blocking effect on sodium channels.

The objectives of this study were to investigate the inhibitory action of capsaicin on wild-type (WT) and mutation human ether-a-go-go -related gene (hERG) potassium channel currents ( I hERG ), and to determine whether mutations in the S6 region are significant for the inhibition of I hERG by capsaicin. The hERG channel (WT, Y652A and F656A) was expressed in Xenopus oocytes and studied using standard two-microelectrode voltage-clamp techniques. The results show that capsaicin blocks WT hERG in a concentration-dependent manner, with an IC 50 of 17.45 μM and a negative shift in the steady-state inactivation curve. Characteristics of blockade were consistent with capsaicin causing components of block in both the closed and open channel states. However, mutating the Y652 residue to Ala enhances the blockade effect of capsaicin with an IC 50 of 4.11 μM, whereas mutation of F656A does not significantly alter drug potency. Simultaneously, for Y652A, the steady-state activation parameter is shifted to a more positive value by 5 mV and the inactivation parameter is shifted to a more negative value by − 29 mV in the presence of 25 μM capsaicin. In conclusion, capsaicin blocks hERG channels by binding to both the closed and open channel states.Y652 was important as a molecular determinant of blockade. Mutation Y652A enhances the drug block, which may cause some patients to be particularly sensitive to capsaicin clinically.