1 Electrophysiological effects of MS-551, a new class III antiarrhythmic drug, were examined and compared with those of (+)-sotalol in rabbit ventricular cells. 2 In rabbit ventricular muscles stimulated at 1.0 Hz, MS-551 (0.1-10 LM) and (+)-sotalol (3-100I1M) prolonged action potential duration (APD) and effective refractory period without affecting the maximum upstroke velocity of phase 0 depolarization (V.,a). The class III effect of MS-551 was approximately 30 times more potent than that of (+)-sotalol. 3 Class III effects of MS-551 and (+)-sotalol showed reverse use-dependence, i.e., a greater prolongation of APD at a longer cycle length. 4 In rabbit isolated ventricular cells, 3 gM MS-551 and 100 JLM sotalol inhibited the delayed rectifier potassium current (IK) which was activated at more positive potentials than -50 mV and saturated around + 20 mV. 5 MS-551 at a higher concentration of 10 JAM decreased the transient outward current (Ito) and the inward rectifier potassium current (IKI) although 100 tLM sotalol failed to inhibit these currents.6 MS-551 is a non-specific class III drug which can inhibit three voltage-gated K+ channels in rabbit ventricular cells.
Type-I interferons (IFNs) and the interferon-stimulated genes (ISGs) play a major role in antivirus responses against hepatitis C virus (HCV) infection. In this study, we studied expression profiles of ISGs in cells supporting subgenomic HCV replication (Huh7/Rep), and screened their activities to suppress HCV replication. Real-time PCR analyses showed that the expression levels of 23 ISGs were significantly lower in Huh7/Rep than naive Huh7 cells due to transcriptional suppression of the interferon-stimulated response element (ISRE). Furthermore, the expression level of ISGs was also decreased in the cured Huh7 cells in which replicon had been eliminated (cHuh7), indicating adaptation of the cells to support HCV replication by downregulating ISGs. On the other hand, expression of HCV replicon was significantly suppressed by overexpression of several ISGs including PKR, MxA, IRF-9, GBP-1, IFI-6-16, IFI-27, 25OAS and IRF-1. Knock down of GBP-1, IFI-6-16 and IFI-27 by short hairpin RNA resulted in increase of HCV replication. Thus, we conclude that downregulation of ISG expression is required in the host cells supporting HCV replication and that several ISGs directly suppress HCV replication. The search for ISGs that regulate HCV replication may help to elucidate the cellular antiviral defence mechanisms against HCV infection.
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