A possible mechanism of halocarbon-induced cardiac sensitization arrhythmias

1,1-Difluoroethane Hydrocarbon Cardiomyopathy

1,1-Difluoroethane (DFE) cardiomyopathy results from the direct inhalation of toxic halogenated hydrocarbons. We present a case series of acute DFE cardiomyopathy illustrating the typical presentation of severe DFE cardiomyopathy along with a detailed description of its mechanism of injury. (Level of Difficulty: Advanced.).

Inhalants

Toxic inhalants include various xenobiotics. Irritants cause upper and lower respiratory tract injuries. Highly water-soluble agents injure the upper respiratory tract, while low water-soluble inhalants injure the lower track. Asphyxiants are divided into simple asphyxiants and chemical asphyxiants. Simple asphyxiants displace oxygen, causing hypoxia, while chemical asphyxiants also impair the body's ability to use oxygen. Cyanide is a classic chemical asphyxiant. Treatment includes hydroxocobalamin. Electronic cigarette or vaping use-associated lung injury (EVALI) is a relatively new illness. Patients present with respiratory symptoms and gastrointestinal distress. EVALI appears to be associated with vaping cannabinoids. Treatment is supportive and may include steroids.

Chloroform is a potent activator of cardiac and neuronal Kir3 channels

Chloroform has been used over decades in anesthesia before it was replaced by other volatile anesthetics like halothane or sevoflurane. Some of the reasons were inadmissible side effects of chloroform like bradycardia or neural illness. In the present study, we identified members of the G protein-activated inwardly rectifying potassium channel family (Kir3) expressed in Xenopus oocytes as potential common molecular targets for both the neural and cardiac effects of chloroform. Millimolar concentration currents representing a 1:10000 dilution of commercially available chloroform were used in laboratories that augment neuronal Kir3.1/3.2 currents as well as cardiac Kir3.1/3.4. This effect was selective and only observed in currents from Kir3 subunits but not in currents from Kir2 subunits. Augmentation of atrial Kir3.1/3.4 currents leads to an effective drop of the heart rate and a reduction in contraction force in isolated mouse atria.

Two Cases of Chloral Hydrate Overdose

Chloral hydrate overdose is associated with cardiac toxicities, gastrointestinal tract injuries, central nervous system and respiratory depression. Among all the complications, cardiac arrhythmias are particularly concerning and frequently reported in the literature. The majorities of fatalities from chloral hydrate overdose are due to refractory cardiac arrhythmia. Chloral hydrate-induced arrhythmias are resistant to most of the standard anti-arrhythmic agents but have good response to propranolol. We report two cases of severe chloral hydrate overdose presenting with alarming cardiac rhythm disturbances. One of the patients was successfully treated with intravenous propranolol in the accident and emergency department. The management of chloral hydrate overdose in particular to its cardiac toxicity is reviewed.

Inhibitory effect of gap junction blockers on cerebral vasospasm

OBJECT

The gap junction is important in the propagation of dilation/constriction signals along vessels for coordinated behavior in control of vascular tone. The authors hypothesized that gap junctions might play a role in cerebral vasospasm following subarachnoid hemorrhage (SAH). The aims of the present study were to investigate the role of gap junctions and to observe the potential therapeutic efficacy of gap junction blockers in cerebral vasospasm in vitro and in vivo.

METHODS

For the in vitro investigation, the effect of heptanol on the oxyhemoglobin (HbO(2))-induced contraction of isolated rabbit basilar arteries (BAs) was observed by using an isometric tension-recording method. For the in vivo experiments, the potential therapeutic efficacy of heptanol and carbenoxolone was surveyed after it was given intravenously in the rabbit double-hemorrhage model. Light microscopy was performed to assess the morphological changes in the arteries examined.

RESULTS

For the in vitro method, heptanol significantly inhibited the sustained contraction induced both by HbO(2) and K(+) in the BA rings. The magnitude of the heptanol-induced relaxation was dose dependent. The inhibitory effect of heptanol on the K(+)-induced vasoconstriction was weaker than that on the HbO(2)-induced constriction. After arterial rings were pretreated for 10 minutes, heptanol significantly decreased their responses to the HbO(2)-induced contraction. For the in vivo method, heptanol and carbenoxolone significantly decreased the narrowing of BAs when given intravenously in the rabbit double-hemorrhage model. In both treated groups, the diameters of the arteries had not changed significantly on Day 7 compared with those of the arteries in the SAH + vehicle and the SAH-only group.

CONCLUSIONS

Heptanol and carbenoxolone significantly inhibited the experimental cerebral vasospasm both in vitro and in vivo. Blockage of gap junctions is a probable candidate for a new approach in the treatment of cerebral vasospasm. Gap junctions may play a pathophysiological role in cerebral vasospasm.

NF-kappaB-dependent transcriptional regulation of the cardiac scn5a sodium channel by angiotensin II

Angiotensin II (ANG II) increases oxidative stress and is associated with increased risk of sudden cardiac death. The cardiac Na(+) channel promoter contains elements that confer redox sensitivity. We tested the hypothesis that ANG II-mediated oxidative stress may modulate Na(+) channel current through altering channel transcription. In H9c2 myocytes treated for 48 h with ANG II (100 nmol/l) or H(2)O(2) (10 micromol/l) showed delayed macroscopic inactivation, increased late current, and 59.6% and 53.8% reductions in Na(+) current, respectively (P < or = 0.01). By quantitative real-time RT-PCR, the cardiac Na(+) channel (scn5a) mRNA abundance declined by 47.3% (P < 0.01) in H9c2 myocytes treated for 48 h with 100 nmol/l ANG II. A similar change occurred with 20 micromol/l H(2)O(2) (46.9%, P < 0.01) after 48 h. Comparable effects were seen in acutely isolated ventricular myocytes. The effects of ANG II could be inhibited by prior treatment of H9c2 cells with scavengers of reactive oxygen species or an inhibitor of the NADPH oxidase. Mutation of the scn5a promoter NF-kappaB binding site prevented decreased activity in response to ANG II and H(2)O(2). Gel shift and chromosomal immunoprecipitation assays confirmed that nuclear factor (NF)-kappaB bound to the scn5a promoter in response to ANG II and H(2)O(2). Overexpression of the p50 subunit of NF-kappaB in H9c2 cells reduced scn5a mRNA (77.3%, P < 0.01). In conclusion, ANG II can decrease scn5a transcription and current. This effect appears to be through production of H(2)O(2) resulting in NF-kappaB binding to the Na(+) channel promoter.

Human heart failure is associated with abnormal C-terminal splicing variants in the cardiac sodium channel

Heart failure (HF) is associated with reduced cardiac Na+ channel (SCN5A) current. We hypothesized that abnormal transcriptional regulation of this ion channel during HF could help explain the reduced current. Using human hearts explanted at the transplantation, we have identified 3 human C-terminal SCN5A mRNA splicing variants predicted to result in truncated, nonfunctional channels. As compared with normal hearts, the explanted ventricles showed an upregulation of 2 of the variants and a downregulation of the full-length mRNA transcript such that the E28A transcript represented only 48.5% (P<0.01) of the total SCN5A mRNA. This correlated with a 62.8% (P<0.01) reduction in Na+ channel protein. Lymphoblasts and skeletal muscle expressing SCN5A also showed identical C-terminal splicing variants. Variants showed reduced membrane protein and no functional current. Transfection of truncation variants into a cell line stably transfected with the full-length Na+ channel resulted in dose-dependent reductions in channel mRNA and current. Introduction of a premature truncation in the C-terminal region in a single allele of the mouse SCN5A resulted in embryonic lethality. Embryonic stem cell-derived cardiomyocytes expressing the construct showed reductions in Na+ channel-dependent electrophysiological parameters, suggesting that the presence of truncated Na+ channel mRNA at levels seen in HF is likely to be physiologically significant. In summary, chronic HF was associated with an increase in 2 truncated SCN5A variants and a decrease in the native mRNA. These splice variations may help explain a loss of Na+ channel protein and may contribute to the increased arrhythmic risk in clinical HF.