Remodelling and dysfunction of the sinus node in pulmonary arterial hypertension.

Patients with pulmonary arterial hypertension (PAH) have a high burden of arrhythmias, including arrhythmias arising from sinus node dysfunction, and the aim of this study was to investigate the effects of PAH on the sinus node. In the rat, PAH was induced by an injection of monocrotaline. Three weeks after injection, there was a decrease of the intrinsic heart rate (heart rate in the absence of autonomic tone) as well as the normal heart rate, evidence of sinus node dysfunction. In the sinus node of PAH rats, there was a significant downregulation of many ion channels and Ca2+-handling genes that could explain the dysfunction: HCN1 and HCN4 (responsible for pacemaker current, If), Cav1.2, Cav1.3 and Cav3.1 (responsible for L- and T-type Ca2+ currents, ICa,L and ICa,T), NCX1 (responsible for Na+-Ca2+ exchanger) and SERCA2 and RYR2 (Ca2+-handling molecules). In the sinus node of PAH rats, there was also a significant upregulation of many fibrosis genes that could also help explain the dysfunction: vimentin, collagen type 1, elastin, fibronectin and transforming growth factor ß1. In summary, in PAH, there is a remodelling of ion channel, Ca2+-handling and fibrosis genes in the sinus node that is likely to be responsible for the sinus node dysfunction. This article is part of the theme issue 'The heartbeat: its molecular basis and physiological mechanisms'.

Atrioventricular Node Dysfunction and Ion Channel Transcriptome in Pulmonary Hypertension.

BACKGROUND: Heart block is associated with pulmonary hypertension, and the aim of the study was to test the hypothesis that the heart block is the result of a change in the ion channel transcriptome of the atrioventricular (AV) node. METHODS AND RESULTS: The most commonly used animal model of pulmonary hypertension, the monocrotaline-injected rat, was used. The functional consequences of monocrotaline injection were determined by echocardiography, ECG recording, and electrophysiological experiments on the Langendorff-perfused heart and isolated AV node. The ion channel transcriptome was measured by quantitative PCR, and biophysically detailed computer modeling was used to explore the changes observed. After monocrotaline injection, echocardiography revealed the pattern of pulmonary artery blood flow characteristic of pulmonary hypertension and right-sided hypertrophy and failure; the Langendorff-perfused heart and isolated AV node revealed dysfunction of the AV node (eg, 50% incidence of heart block in isolated AV node); and quantitative PCR revealed a widespread downregulation of ion channel and related genes in the AV node (eg, >50% downregulation of Cav1.2/3 and HCN1/2/4 channels). Computer modeling predicted that the changes in the transcriptome if translated into protein and function would result in heart block. CONCLUSIONS: Pulmonary hypertension results in a derangement of the ion channel transcriptome in the AV node, and this is the likely cause of AV node dysfunction in this disease.

Oral administration of eicosapentaenoic acid or docosahexaenoic acid modifies cardiac function and ameliorates congestive heart failure in male rats.

This study assessed the effects of eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) on normal cardiac function (part 1) and congestive heart failure (CHF) (part 2) through electrocardiogram analysis and determination of EPA, DHA, and arachidonic acid (AA) concentrations in rat hearts. In part 2, pathologic assessments were also performed. For part 1 of this study, 4-wk-old male rats were divided into a control group and 2 experimental groups. The rats daily were orally administered (1 g/kg body weight) saline, EPA-ethyl ester (EPA-Et; E group), or DHA-ethyl ester (DHA-Et; D group), respectively, for 28 d. ECGs revealed that QT intervals were significantly shorter for groups E and D compared with the control group (P ≤ 0.05). Relative to the control group, the concentration of EPA was higher in the E group and concentrations of EPA and DHA were higher in the D group, although AA concentrations were lower (P ≤ 0.05). In part 2, CHF was produced by subcutaneous injection of monocrotaline into 5-wk-old rats. At 3 d before monocrotaline injection, rats were administered either saline, EPA-Et, or DHA-Et as mentioned above and then killed at 21 d. The study groups were as follows: normal + saline (control), CHF + saline (H group), CHF + EPA-Et (HE group), and CHF + DHA-Et (HD group). QT intervals were significantly shorter (P ≤ 0.05) in the control and HD groups compared with the H and HE groups. Relative to the H group, concentrations of EPA were higher in the HE group and those of DHA were higher in the control and HD groups (P ≤ 0.05). There was less mononuclear cell infiltration in the myocytes of the HD group than in the H group (P = 0.06). The right ventricles in the H, HE, and HD groups showed significantly increased weights (P ≤ 0.05) compared with controls. The administration of EPA-Et or DHA-Et may affect cardiac function by modification of heart fatty acid composition, and the administration of DHA-Et may ameliorate CHF.

Effects of squalene/squalane on dopamine levels, antioxidant enzyme activity, and fatty acid composition in the striatum of Parkinson's disease mouse model.

Active oxygen has been implicated in the pathogenesis of Parkinson's disease (PD); therefore, antioxidants have attracted attention as a potential way to prevent this disease. Squalene, a natural triterpene and an intermediate in the biosynthesis of cholesterol, is known to have active oxygen scavenging activities. Squalane, synthesized by complete hydrogenation of squalene, does not have active oxygen scavenging activities. We examined the effects of oral administration of squalene or squalane on a PD mouse model, which was developed by intracerebroventricular injection of 6-hydroxydopamine (6-OHDA). Squalene administration 7 days before and 7 days after one 6-OHDA injection prevented a reduction in striatal dopamine (DA) levels, while the same administration of squalane enhanced the levels. Neither squalene nor squalane administration for 7 days changed the levels of catalase, glutathione peroxidase, or superoxide dismutase activities in the striatum. Squalane increased thiobarbituric acid reactive substances, a marker of lipid peroxidation, in the striatum. Both squalane and squalene increased the ratio of linoleic acid/linolenic acid in the striatum. These results suggest that the administration of squalene or squalane induces similar changes in the composition of fatty acids and has no effect on the activities of active oxygen scavenging enzymes in the striatum. However, squalane increases oxidative damage in the striatum and exacerbates the toxicity of 6-OHDA, while squalene prevents it. The effects of squalene or squalane treatment in this model suggest their possible uses and risks in the treatment of PD.

Effects of zingerone [4-(4-hydroxy-3-methoxyphenyl)-2-butanone] and eugenol [2-methoxy-4-(2-propenyl)phenol] on the pathological progress in the 6-hydroxydopamine-induced Parkinson's disease mouse model.

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons in the nigrostriatal system and dopamine (DA) depletion in the striatum. The most popular therapeutic medicine for treating PD, 3-(3,4-Dihydroxyphenyl)-L-alanine (L-DOPA), has adverse effects, such as dyskinesia and disease acceleration. As superoxide (·O(2)(-)) and hydroxyl radical (·OH) have been implicated in the pathogenesis of PD, free radical scavenging and antioxidants have attracted attention as agents to prevent disease progression. Rodents injected with 6-hydroxydopamine (6-OHDA) intracerebroventricularly are considered to be a good animal model of PD. Zingerone and eugenol, essential oils extracted from ginger and cloves, are known to have free radical scavenging and antioxidant effects. Therefore, we examined the effects of zingerone and eugenol on the behavioral problems in mouse model and on the DA concentration and antioxidant activities in the striatum after 6-OHDA administration and L-DOPA treatment. Daily oral administration of eugenol/zingerone and injection of L-DOPA intraperitoneally for 4 weeks following a single 6-OHDA injection did not improve abnormal behaviors induced by L-DOPA treatment. 6-OHDA reduced the DA level in the striatum; surprisingly, zingerone and eugenol enhanced the reduction of striatal DA and its metabolites. Zingerone decreased catalase activity, and increased glutathione peroxidase activity and the oxidized L-ascorbate level in the striatum. We previously reported that pre-treatment with zingerone or eugenol prevents 6-OHDA-induced DA depression by preventing lipid peroxidation. However, the present study shows that post-treatment with these substances enhanced the DA decrease. These substances had adverse effects dependent on the time of administration relative to model PD onset. These results suggest that we should be wary of ingesting these spice elements after the onset of PD symptoms.

In vivo tissue uptake of intravenously injected water soluble all-trans beta-carotene used as a food colorant.

Water soluble beta-carotene (WS-BC) is a carotenoid form that has been developed as a food colorant. WS-BC is known to contain 10% of all-trans beta-carotene (AT-BC). The aim of the present study was to investigate in vivo tissue uptake of AT-BC after the administration of WS-BC into rats. Seven-week-old male rats were administered 20 mg of WS-BC dissolved in saline by intravenous injection into the tail vein. At 0, 6, 24, 72, 120 and 168 hours (n = 7/time), blood was drawn and liver, lungs, adrenal glands, kidneys and testes were dissected. The levels of AT-BC in the plasma and dissected tissues were quantified with HPLC. After intravenous administration, AT-BC level in plasma first increased up to 6 h and returned to normal at 72 h. In the testes, the AT-BC level first increased up to 24 h and then did not decrease but was retained up to 168 h. In the other tissues, the level first increased up to 6 h and then decreased from 6 to 120 or 168 h but did not return to normal. The accumulation of WS-BC in testes but not in the other 5 tissues examined may suggest that AT-BC was excreted or metabolized in these tissues but not in testes. Although WS-BC is commonly used as a food colorant, its effects on body tissues are still not clarified. Results of the present study suggest that further investigations are required to elucidate effects of WS-BC on various body tissues.

Docosahexaenoic acid ethyl ester enhances 6-hydroxydopamine-induced neuronal damage by induction of lipid peroxidation in mouse striatum.

Superoxide and hydroxyl radicals are implicated in the pathogenesis of Parkinson disease, and induction of lipid peroxidation is an important factor in progression of this disease. Docosahexaenoic acid (DHA) is a key component of the cell membrane, and its peroxidation is inducible due to the double-bond chemical structure. However, DHA has neuroprotective effects. In this study, we examined the effects of intraperitoneal injection (ipi) of DHA ethyl ester (DHA-Et) on 6-hydroxydopamine (6-OHDA)-induced dopamine (DA) reduction in the mouse striatum. DHA-Et ipi for 7 days before and 7 days after a single intracerebroventricular injection of 6-OHDA enhanced 6-OHDA-induced reduction of striatal DA level. On the other hand, ipi of DHA-Et for 7 days increased its concentration in the striatum. Co-injection of DHA-Et and 6-OHDA increased the levels of thiobarbituric acid-reactive substances (a marker of lipid peroxidation) in the striatum. Our results suggest that DHA-Et enhances 6-OHDA-induced DA depression by increasing lipid peroxidation, and that excessive use of DHA-Et may increase the susceptibility of Parkinson disease in animal model.

Localization of Na+ channel isoforms at the atrioventricular junction and atrioventricular node in the rat.

BACKGROUND: The electrical activity of the atrioventricular node (AVN) is functionally heterogeneous, but how this relates to distinct cell types and the 3-dimensional structure of the AVN is unknown. To address this, we have studied the expression of Na(V)1.5 and other Na+ channel isoforms in the AVN. METHODS AND RESULTS: The rat AVN was identified by Masson's trichrome staining together with immunolabeling of marker proteins: connexin40, connexin43, desmoplakin, atrial natriuretic peptide, and hyperpolarization-activated and cyclic nucleotide-gated channel 4. Na+ channel expression was investigated with immunohistochemistry with isoform-specific Na+ channel antibodies. Na(V)1.1 was distributed in a similar manner to Na(V)1.5. Na(V)1.2 was not detected. Na(V)1.3 labeling was present in nerve fibers and cell bodies (but not myocytes) and was abundant in the penetrating atrioventricular (AV) bundle and the common bundle but was much less abundant in other regions. Na(V)1.5 labeling was abundant in the atrial and ventricular myocardium and the left bundle branch. Na(V)1.5 labeling was absent in the open node, penetrating AV bundle, AV ring bundle, and common bundle but present at a reduced level in the inferior nodal extension and transitional zone. Na(V)1.6 was not detected. CONCLUSIONS: Our findings provide molecular evidence of multiple electrophysiological cell types at the AV junction. Impaired AV conduction as a result of mutations in or loss of Na(V)1.5 must be the result of impaired conduction in the AVN inputs (inferior nodal extension and transitional zone) or output (bundle branches) rather than the AVN itself (open node and penetrating AV bundle).

K(+) current distribution in rat sub-epicardial ventricular myocytes.

In the rat ventricle, the transient outward K(+) current ( I(TO)) is carried by heteromeric channels composed of Kv4.2 and Kv4.3. However its distribution in the cell membrane is unclear: immunohistochemical studies of Kv4.2 distribution in the cardiac ventricular cell membrane have given equivocal results, and there are no corresponding studies of Kv4.3. We therefore used detubulated cardiac cells to investigate the functional distribution of I(TO) between the t-tubules and surface membrane. I(TO), the delayed rectifier ( I(K)), the inward rectifier ( I(K1)) and steady-state ( I(SS)) K(+) currents were monitored using the patch-clamp technique in control and formamide-treated (detubulated) cells from rat left ventricular sub-epicardium. Formamide treatment decreased cell capacitance by 20%, did not significantly change the density of I(TO), I(K) or I(K1) but decreased the density of I(SS) and L-type Ca current ( I(Ca)). These data suggest that I(TO), I(K), and I(K1) are uniformly distributed between the surface and t-tubule membranes, but that I(SS) and I(Ca) are concentrated in the t-tubules.