Abstract-In the heart, oxidative stress caused by exogenous H 2 O 2 has been shown to induce early afterdepolarizations (EADs) and triggered activity by impairing Na current (I Na ) inactivation. Because H 2 O 2 activates Ca 2ϩ /calmodulin kinase (CaMK)II, which also impairs I Na inactivation and promotes EADs, we hypothesized that CaMKII activation may be an important factor in EADs caused by oxidative stress. Using the patch-clamp and intracellular Ca (Ca i ) imaging in Fluo-4 AM-loaded rabbit ventricular myocytes, we found that exposure to H 2 O 2 (0.2 to 1 mmol/L) for 5 to 15 minutes consistently induced EADs that were suppressed by the I Na blocker tetrodotoxin (10 mol/L), as well as the I Ca,L blocker nifedipine. H 2 O 2 enhanced both peak and late I Ca,L , consistent with CaMKII-mediated facilitation. By prolonging the action potential plateau and increasing Ca influx via I Ca,L , H 2 O 2 -induced EADs were also frequently followed by DADs in response to spontaneous (ie, non-I Ca,L -gated) sarcoplasmic reticulum Ca release after repolarization. The CaMKII inhibitor (1 mol/L; nϭ4), but not its inactive analog (1 mol/L, nϭ5), prevented H 2 O 2 -induced EADs and DADs, and the selective CaMKII peptide inhibitor AIP (autocamtide-2-related inhibitory peptide) (2 mol/L) significantly delayed their onset. In conclusion, H 2 O 2 -induced afterdepolarizations depend on both impaired I Na inactivation to reduce repolarization reserve and enhancement of I Ca,L to reverse repolarization, which are both facilitated by CaMKII activation.

A new adsorbent, bead cellulose loaded with iron oxyhydroxide (BCF), was prepared and applied for the adsorption and removal of arsenate and arsenite from aqueous systems. The continuing loading process of Fe in the cellulose beads was realized through hydrolization of ferric salts when alkaline solution was added dropwise. Spherical BCF had excellent mechanical and hydraulic properties. Akaganeite (beta-FeOOH), the reactive center of BCF that was stably loaded into the cellulose, had a high sensitivity to arsenite as well as arsenate. The maximum content of Fe in BCF reached 50% (w/w). In this study we investigated the adsorption behavior of arsenite and arsenate on BCF, including adsorption isotherms, adsorption kinetics, the influence of pH and competing anions on adsorption, and column experiments. The adsorption data accorded with both Freundlich and Langmuir isotherms. The adsorption capacity for arsenite and arsenate was 99.6 and 33.2 mg/g BCF at pH 7.0 with an Fe content of 220 mg/ mL. Kinetic data fitted well to the pseudo-second-order reaction model. Arsenate elimination was favored at acidic pH, whereas the adsorption of arsenite by BCF was found to be effective in a wide pH range of 5-11. Under the experimental conditions, the addition of sulfate had no effect on arsenic adsorption, whereas phosphate greatly influenced the elimination of both arsenite and aresenate. Silicate moderately decreased the adsorption of arsenite, but not arsenate. Both batch experiments and column experiments indicated that BCF had higher removal efficiency for arsenite than for arsenate. While the influent contaminant concentration was 500 microg/L in groundwater and the empty-bed contact time (EBCT) for arsenite and arsenate was 4.2 and 5.9 min, breakthrough empty-bed volumes at the WHO provisional guideline value of 10 microg/L were 2200 and 5000, respectively. BCF can be effectively regenerated when elution is done with 2 M NaOH solution. The column experiments for four cycles showed that stable and high removal efficiency of arsenic was sustained by BCF after regeneration.

Oxidative stress with hydrogen peroxide (H(2)O(2)) readily promotes early afterdepolarizations (EADs) and triggered activity (TA) in isolated rat and rabbit ventricular myocytes. Here we examined the effects of H(2)O(2) on arrhythmias in intact Langendorff rat and rabbit hearts using dual-membrane voltage and intracellular calcium optical mapping and glass microelectrode recordings. Young adult rat (3-5 mo, N = 25) and rabbit (3-5 mo, N = 6) hearts exhibited no arrhythmias when perfused with H(2)O(2) (0.1-2 mM) for up to 3 h. However, in 33 out of 35 (94%) aged (24-26 mo) rat hearts, 0.1 mM H(2)O(2) caused EAD-mediated TA, leading to ventricular tachycardia (VT) and fibrillation (VF). Aged rabbits (life span, 8-12 yr) were not available, but 4 of 10 middle-aged rabbits (3-5 yr) developed EADs, TA, VT, and VF. These arrhythmias were suppressed by the reducing agent N-acetylcysteine (2 mM) and CaMKII inhibitor KN-93 (1 microM) but not by its inactive form (KN-92, 1 microM). There were no significant differences between action potential duration (APD) or APD restitution slope before or after H(2)O(2) in aged or young adult rat hearts. In histological sections, however, trichrome staining revealed that aged rat hearts exhibited extensive fibrosis, ranging from 10-90%; middle-aged rabbit hearts had less fibrosis (5-35%), whereas young adult rat and rabbit hearts had <4% fibrosis. In aged rat hearts, EADs and TA arose most frequently (70%) from the left ventricular base where fibrosis was intermediate ( approximately 30%). Computer simulations in two-dimensional tissue incorporating variable degrees of fibrosis showed that intermediate (but not mild or severe) fibrosis promoted EADs and TA. We conclude that in aged ventricles exposed to oxidative stress, fibrosis facilitates the ability of cellular EADs to emerge and generate TA, VT, and VF at the tissue level.

Na,K-ATPase is an essential gene maintaining electrochemical gradients across the plasma membrane. Although previous studies have intensively focused on the role of Na,K-ATPase in regulating cardiac function in the adults, little is known about the requirement for Na,KATPase during embryonic heart development. Here, we report the identification of a zebrafish mutant, heart and mind, which exhibits multiple cardiac defects, including the primitive heart tube extension abnormality, aberrant cardiomyocyte differentiation, and reduced heart rate and contractility. Molecular cloning reveals that the heart and mind lesion resides in the α1B1 isoform of Na,K-ATPase. Blocking Na,K-ATPase α1B1 activity by pharmacological means or by morpholino antisense oligonucleotides phenocopies the patterning and functional defects of heart and mind mutant hearts, suggesting crucial roles for Na,KATPase α1B1 in embryonic zebrafish hearts. In addition to α1B1, the Na,K-ATPase α2 isoform is required for embryonic cardiac patterning. Although the α1B1 and α2 isoforms share high degrees of similarities in their coding sequences, they have distinct roles in patterning zebrafish hearts. The phenotypes of heart and mind mutants can be rescued by supplementing α1B1, but not α2, mRNA to the mutant embryos, demonstrating that α1B1 and α2 are not functionally equivalent. Furthermore, instead of interfering with primitive heart tube formation or cardiac chamber differentiation, blocking the translation of Na,KATPase α2 isoform leads to cardiac laterality defects. Supplemental figure available online