- Email: [email protected]
TNF-α induces ion channel (Ito) down-regulation in myocyte independently on the Reactive Oxygen Species (ROS) generation
Poster 5 (class III and IV) heart failure despite optimal medical therapy is well established. This case report describes the use of cardiac resynchronization therapy to treat symptomatic congestive heart failure in two patients with congenitally corrected transposition of the great vessels Both patients had drug refractory congestive heart failure. A transvenous system was placed into the coronary sinus lateral wall branch of both patietns. In one patietn a baloon occlusive venogram was performed, and in another, teh coronary sinus was seen with coronary angiography and levophase visualization. Both patients had a significant improvment in their functional class. More patients with CCTGV are surviving to adulthood and developing symptomatic heart failure that exceeds the limits of medical therapy. Since these patients are unlikely to be transplant candidates, alternate strategies need to be deployed to improve symptoms and quality of life. CRT has improved the quality of life and symptoms from heart failure in patients with Class III to IV heart failure and ventricular dyssynchrony in patients without congenital heart disease. This case report opens the possibility that this technology will be beneficial in patients with CCGTV that have ventricular dyssynchrony and symptomatic heart failure.
S255 and Ito-related molecules, and the regulation of action potential duration (APD) in neonatal rat myocytes. Methods: The ventricular myocytes were isolated from 1⬃2-day-old Lewis rat and incubated for 72h. Then, the cells were treated with TNF-␣ (50ng/ml) for 48h after preincubation with NAC (1nM) for 1h. Ito density and APD was measured by the patch-clamp technique and cell-size was evaluated by measurement of cell-capacitance and area of microscopic image. The expression of Kv4.2 was analyzed by real time RT-PCR. Results: TNF-␣ caused hypertrophy, APD prolongation and Ito reduction in myocytes. With the NAC pretreatment, TNF-␣ induced hypertrophy was totally inhibited (cell area: TNF-␣; 3424⫾1084, NAC⫹TNF-␣; 2386⫾772m2, p⬍0.0001). In contrast, NAC pretreatment did not prevent TNF-␣ induced electrical remodeling, i.e., APD prolongation (APD90: TNF-␣; 186⫾48, NAC⫹TNF-␣; 143⫾28ms, p⫽0.220), Ito-reduction (peak current: TNF-␣; 11.0 ⫾ 2.9, NAC⫹TNF-␣: 9.07 ⫾ 3.4pA/pF, NS), and reduction of Kv4.2 mRNA expression. Conclusion: NAC inhibited TNF-␣ induced cellular hypertrophy but not the electrophysiological changes, i.e, Ito reduction and APD prolongation. This indicates that TNF-␣-induced Ito and Kv4.2 down-regulation is mediated by different pathway from the ROS generation systems.
P5-2 NOVEL INTRINSIC MECHANISM OF THE ENHANCED RATEDEPENDENT QT SHORTENING IN R1623Q MUTANT OF THE LQT3 SYNDROME Toshihisa Nagatomo, MD, Yasushi Oginosawa, MD, Haruhiko Abe, MD, Takuo Tsurugi, MD, Kan Kikuchi, MD, Kazunobu Kawakami, MD, Hiroko Takemasa, MD and Yasuhide Nakashima, MD. University of Occupational and Environmental Health, Kitakyushu, Japan.
POSTER SESSION 5 Friday, May 6, 2005 Session Time: 2:00 p.m.–5:00 p.m. Presenter Available: 3:45 p.m.– 4:45 p.m. Location: Exhibit Hall P5-1 TNF-␣ INDUCES ION CHANNEL (ITO) DOWN-REGULATION IN MYOCYTE INDEPENDENTLY ON THE REACTIVE OXYGEN SPECIES (ROS) GENERATION Masaru Yuge, MD, Shinichi Niwano, MD, Hiroe Niwano, MD, Hideaki Kawada, Yoshihiro Yumoto, MD, Yuko Wakisaka, MD and Tohru Izumi. Kitasato University, Sagamihara, Japan. Background: We have reported that TNF-␣ caused down-regulation of transient outward current (Ito) as well as hypertrophy in cultured neonatal myocytes. Although TNF-␣ induced hypertrophy was reported to be mediated by the activation of reactive oxygen speicies (ROS), the mechanism regulating ion channel is unclear. In this study, we evaluated the effect of n-acetyl cystein (NAC), an antioxidant, on TNF-␣ induced reduction of Ito
Objective: In type 3 long QT syndrome (LQT3), arrhythmia events tend to occur at rest or during sleep. One of the mutations, R1623Q, is located in the voltage sensor of the cardiac sodium channel (hH1) and patients with R1623Q mutation has been also reported to show bradycardia-dependent cardiac events. Although the mutant channel has been characterized by inactivation gating defects, the intrinsic mechanism(s) that might explain why arrhythmia attack is most prevalent at slower heart rates has not been investigated. Methods: cDNA encoding either wild-type (WT) or R1623Q mutant of hH1 was stably transfected into HEK293 cells. INa was recorded using a whole-cell patch-clamp technique at 23°C. Results: A train of 50 depolarizing pulses from holding potentials (HP⫽120, -80 mV) to -20 mV or a train of 50 action potential waveforms (HP⬇-85 mV) was applied at different frequencies. When using rectangular waveform voltage clamp, rate-dependent reduction of INa was holding voltage-dependent but was not different between peak and late INa. However, using the action potential clamp, preferential rate-dependent reduction of phase 3 INa in the R1623Q mutant was obvious as compared with peak INa. To elucidate this discrepancy between protocols, time course of recovery from inactivation for WT and R1623Q mutant were studied with a two-pulse protocol (HP, recovery potential ⫽-120, -100 and -80 mV). The recovery time constants were significantly increased at depolarized HPs in both WT and the R1623Q mutant. However, R1623Q mutant channels showed smaller voltage-dependence of recovery compared with WT resulting in a faster recovery from inactivation at a depolarized HP ( N.S. at -120 mV, P ⬍0.05 at -100 mV and P ⬍0.0001 at -80 mV, respectively). Conclusion: Preferential rate-dependent reduction of phase 3 INa was attributed to accelerated recovery from inactivation under non-equilibrium gating. The mechanism may explain the enhanced rate-dependent QTshortening in LQT3 patients. Our findings are important for genotypephenotype correlations in LQT3 mutants as well as for understanding the function of S4 segment of domain IV region in the cardiac Na⫹ channel.
S255 and Ito-related molecules, and the regulation of action potential duration (APD) in neonatal rat myocytes. Methods: The ventricular myocytes were isolated from 1⬃2-day-old Lewis rat and incubated for 72h. Then, the cells were treated with TNF-␣ (50ng/ml) for 48h after preincubation with NAC (1nM) for 1h. Ito density and APD was measured by the patch-clamp technique and cell-size was evaluated by measurement of cell-capacitance and area of microscopic image. The expression of Kv4.2 was analyzed by real time RT-PCR. Results: TNF-␣ caused hypertrophy, APD prolongation and Ito reduction in myocytes. With the NAC pretreatment, TNF-␣ induced hypertrophy was totally inhibited (cell area: TNF-␣; 3424⫾1084, NAC⫹TNF-␣; 2386⫾772m2, p⬍0.0001). In contrast, NAC pretreatment did not prevent TNF-␣ induced electrical remodeling, i.e., APD prolongation (APD90: TNF-␣; 186⫾48, NAC⫹TNF-␣; 143⫾28ms, p⫽0.220), Ito-reduction (peak current: TNF-␣; 11.0 ⫾ 2.9, NAC⫹TNF-␣: 9.07 ⫾ 3.4pA/pF, NS), and reduction of Kv4.2 mRNA expression. Conclusion: NAC inhibited TNF-␣ induced cellular hypertrophy but not the electrophysiological changes, i.e, Ito reduction and APD prolongation. This indicates that TNF-␣-induced Ito and Kv4.2 down-regulation is mediated by different pathway from the ROS generation systems.
P5-2 NOVEL INTRINSIC MECHANISM OF THE ENHANCED RATEDEPENDENT QT SHORTENING IN R1623Q MUTANT OF THE LQT3 SYNDROME Toshihisa Nagatomo, MD, Yasushi Oginosawa, MD, Haruhiko Abe, MD, Takuo Tsurugi, MD, Kan Kikuchi, MD, Kazunobu Kawakami, MD, Hiroko Takemasa, MD and Yasuhide Nakashima, MD. University of Occupational and Environmental Health, Kitakyushu, Japan.
POSTER SESSION 5 Friday, May 6, 2005 Session Time: 2:00 p.m.–5:00 p.m. Presenter Available: 3:45 p.m.– 4:45 p.m. Location: Exhibit Hall P5-1 TNF-␣ INDUCES ION CHANNEL (ITO) DOWN-REGULATION IN MYOCYTE INDEPENDENTLY ON THE REACTIVE OXYGEN SPECIES (ROS) GENERATION Masaru Yuge, MD, Shinichi Niwano, MD, Hiroe Niwano, MD, Hideaki Kawada, Yoshihiro Yumoto, MD, Yuko Wakisaka, MD and Tohru Izumi. Kitasato University, Sagamihara, Japan. Background: We have reported that TNF-␣ caused down-regulation of transient outward current (Ito) as well as hypertrophy in cultured neonatal myocytes. Although TNF-␣ induced hypertrophy was reported to be mediated by the activation of reactive oxygen speicies (ROS), the mechanism regulating ion channel is unclear. In this study, we evaluated the effect of n-acetyl cystein (NAC), an antioxidant, on TNF-␣ induced reduction of Ito
Objective: In type 3 long QT syndrome (LQT3), arrhythmia events tend to occur at rest or during sleep. One of the mutations, R1623Q, is located in the voltage sensor of the cardiac sodium channel (hH1) and patients with R1623Q mutation has been also reported to show bradycardia-dependent cardiac events. Although the mutant channel has been characterized by inactivation gating defects, the intrinsic mechanism(s) that might explain why arrhythmia attack is most prevalent at slower heart rates has not been investigated. Methods: cDNA encoding either wild-type (WT) or R1623Q mutant of hH1 was stably transfected into HEK293 cells. INa was recorded using a whole-cell patch-clamp technique at 23°C. Results: A train of 50 depolarizing pulses from holding potentials (HP⫽120, -80 mV) to -20 mV or a train of 50 action potential waveforms (HP⬇-85 mV) was applied at different frequencies. When using rectangular waveform voltage clamp, rate-dependent reduction of INa was holding voltage-dependent but was not different between peak and late INa. However, using the action potential clamp, preferential rate-dependent reduction of phase 3 INa in the R1623Q mutant was obvious as compared with peak INa. To elucidate this discrepancy between protocols, time course of recovery from inactivation for WT and R1623Q mutant were studied with a two-pulse protocol (HP, recovery potential ⫽-120, -100 and -80 mV). The recovery time constants were significantly increased at depolarized HPs in both WT and the R1623Q mutant. However, R1623Q mutant channels showed smaller voltage-dependence of recovery compared with WT resulting in a faster recovery from inactivation at a depolarized HP ( N.S. at -120 mV, P ⬍0.05 at -100 mV and P ⬍0.0001 at -80 mV, respectively). Conclusion: Preferential rate-dependent reduction of phase 3 INa was attributed to accelerated recovery from inactivation under non-equilibrium gating. The mechanism may explain the enhanced rate-dependent QTshortening in LQT3 patients. Our findings are important for genotypephenotype correlations in LQT3 mutants as well as for understanding the function of S4 segment of domain IV region in the cardiac Na⫹ channel.