Rapid component I(Kr) of cardiac delayed rectifier potassium currents in guinea-pig is inhibited by alpha(1)-adrenoreceptor activation via protein kinase A and protein kinase C-dependent pathways.

Ventricular tachyarrhythmias are often precipitated by physical or emotional stress, indicating a link between increased adrenergic stimulation and cardiac ion channel activity. Human ether-a-go-go related gene (hERG) potassium channels conduct the rapid component of delayed rectifier potassium current, I(kr), a crucial component for action potential repolarization. To evaluate the correlation between increased alpha(1)-adrenergic activity and the rapid component of cardiac I(kr), whole-cell patch-clamp recording was performed in isolated guinea-pig ventricular myocytes. Stimulation of alpha(1)-adrenoceptors using phenylephrine (0.1 nM-100 microM) reduced I(kr) current in a dose-dependent manner at 37 degrees C. Phenylephrine (0.1 microM) reduced I(kr) current to 66.83+/-3.16%. Chelerythrine (1 microM), a specific inhibitor of protein kinase C (PKC) completely inhibited the changes in I(kr) trigged by 0.1 microM phenylephrine. KT5720 (2.5 microM), a specific inhibitor of protein kinase A (PKA) partially inhibited the current decrease induced by 0.1 microM phenylephrine. Both chelerythrine and KT5720 drastically reduced the phenylephrine-induced effects, indicating possible involvement of PKC and PKA in the alpha(1)-adrenergic inhibition of I(kr). Our data suggest a link between I(kr) and the alpha(1)-adrenoceptor, involving activation of PKC and PKA in arrhythmogenesis.

Negative regulation of quinone reductase 2 by resveratrol in cultured vascular smooth muscle cells.

1. Resveratrol, a polyphenol in red wine, has a cardioprotective effect. Resveratrol-targeting protein (RTP) has been purified using a resveratrol affinity column (RAC) and has been identified as quinone reductase type 2 (NQO2). We hypothesize that NQO2 is the target protein of resveratrol in vascular smooth muscle cells (VSMC) and that resveratrol inhibits proliferation of VSMC through its action on NQO2. In the present study, we investigated the correlation between NQO2 regulation and cell proliferation in VSMC in response to resveratrol treatment. 2. The RTP was purified using RAC and was detected with a NQO2 polyclonal antibody. The VSMC were incubated with resveratrol (1, 10 and 50 micromol/L) for 24, 48 and 72 h. Cell proliferation was detected by cell counting and bromodeoxyuridine (BrdU) assay. A lentiviral vector incorporating NQO2 short interference (si) RNA of short hairpin design was constructed and transduced into VSMC. Real-time quantitative polymerase chain reaction was used to measure NQO2 mRNA levels; NQO2 expression was determined by western blot analysis. 3. Using RAC, we extracted a 26 kDa protein from aortic smooth muscle, which was referred to as RTP-26. Proliferation of VSMC was inhibited by resveratrol in a concentration- and time-dependent manner. The mRNA and protein expression of NQO2 was also repressed by resveratrol in a concentration- and time-dependent manner. A similar pattern of inhibition was observed for cells treated with resveratrol (25 micromol/L) as for cells transduced with a lentiviral vector containing siRNA sequences against NQO2. 4. Collectively, these data indicate that the suppression of VSMC proliferation mediated by resveratrol correlates with NQO2 downregulation.

Effect of red wine and wine polyphenol resveratrol on endothelial function in hypercholesterolemic rabbits.

The effect of red wine and wine polyphenol resveratrol on endothelial function was investigated in experimental hypercholesterolemic rabbits. Endothelial function as measured by flow-mediated dilation (FMD) in the femoral artery was 19.28+/-2.81% in control animals fed a regular diet. In contrast, rabbits fed a high-cholesterol (1.5%) diet showed a reduced endothelial function, as revealed by a 25% reduction in the measured FMD. Intragastric feeding of resveratrol (3 mg/kg/day), red wine (4 ml/kg/day), dealcoholized red wine (4 ml/kg/day), for 12 weeks in hypercholesterolemic rabbits significantly mitigated the reduction in endothelial function, and resulted in FMD values of 14.52+/-0.60, 18.95+/-2.30, 17.58+/-1.43, and 18.80+/-3.94%, respectively. Measurement of plasma endothelin 1 (ET-1) and nitric oxide (NO) levels showed that feeding a high-cholesterol diet significantly increased plasma ET-1 levels (from 51.4+/-17.6 to 96.9+/-24.3 pg/ml), and decreased plasma NO concentration (from 104.6+/-18.5 to 67.7+/-16.1 pg/ml). With administration of resveratrol, red wine, or dealcoholized red wine, plasma ET-1 levels statistically decreased, in parallel with a significant elevation in NO levels. These results provide in vivo evidence suggesting that resveratrol and red wine improve endothelial function, which may be one of the mechanisms by which this red wine polyphenol exerts its alcohol-independent cardioprotective effects.

Effect of CYP2D6*10 genotype on propafenone pharmacodynamics in Chinese patients with ventricular arrhythmia.

AIM: To determine the effect of CYP2D6*10 genotype on propafenone pharmacodynamics in Chinese patients with ventricular arrhythmia. METHODS: Seventeen Chinese patients with ventricular premature contractions (VPC> or =1000/d) were recruited. They were normal in routine laboratory testing and administered propafenone hydrochloride 450-600 mg per day in three divided doses. Twelve lead cardiogram and 24 h Holter monitoring were performed before and after 7 d treatment of propafenone. Steady-state peak and trough concentrations of propafenone were measured by HPLC method. CYP2D6*10 genotypes of patients were assayed by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP). RESULTS: Total inhibitory rate of VPC was 79.9 % in 17 patients with ventricular arrhythmia after propafenone treatment. PR interval prolongation was increased from 0.146 s+/-0.018 s to 0.161 s+/-0.022 s (P<0.05). CYP2D6 genotypes played an important role in plasma levels and effects of propafenone. In 450 mg/d group, patients with homozygous mutant of CYP2D6*10 not only had a Cmax of propafenone two times as high as those of wild-type genotype, but also showed a two fold higher inhibitory rate of VPC compared with those with homozygous CYP2D6*1 (P<0.05). CONCLUSION: CYP2D6*10 genotype is relevant to decreased activity of CYP2D6 enzyme in Chinese patients. Elevated plasma concentration is consistent with better efficacy of propafenone in patients with ventricular arrhythmia.