ABSTRACT
We studied the effects of the lidocaine on the hERG K+ channels with a focus on the electrophysiology of the heart. The hERG current was recorded using the conventional whole-cell patch clamp technique and the channel protein expression level was measured with Western blot in HEK 293 cells stablely expressed hERG K+ channels. The langendorff perfusion system was used to record the ECG from isolated rabbit heart. Lidocaine inhibited hERG current in a concentration-dependent manner at 0.3-1 000 μmol·L-1, the IC50 value was 88.63±7.99 μmol·L-1. The inhibitory action was enhanced by positive votalge without changing the votalge-dependent activation of the channel. However, lidocaine inhibited hERG current in a frequency-dependent manner. In addition, chronic incubation of lidocaine did not change the hERG K+ channel protein expression. ECG recordings in the isolated perfused rabbit heart demonstrated that lidocaine (> 100 μmol·L-1) did not affected QTc interval, but decreased the heart rate and prolonged the PR interval and QRS duration. Our results demonstrate that lidocaine potentially inhibits the hERG K+ current at a high concentration, but does not prolonged the QTc of ECG.
ABSTRACT
Objective Cardiac HERG potassium channel currents can cause long QT syndrome .The function of the cardiac HERG potassium channel is regulated by tyrosine kinase and phosphatase , and protein tyrosine phosphatase non-receptor type 11 ( PTPN11) negatively regulates the HERG potassium channel .This study aimed to investigate the effect of PTPN 11 on the electrophysio-logical characteristics of the HERG channel . Methods The plasmids of pcDNA3.1-PTPN11-EGFP were constructed by PCR technique and transfected or cotransfected with the pcDNA 3.1-PTPN11-EGFP plasmid into HEK293 cells using Lipofectamine 2000.The patch clamp technique was employed to record the HERG channel currents in the control group ( HEK293 cells transfected with pcDNA3.0-HERG-EGFP), PTPN11 overexpression group (pcDNA3.0-HERG and pcDNA3.1-PTPN6-EGFP cotransfected HEK293 cells), and PTPN11 overexpression with PAO group . Results The pcDNA3.1-PTPN11-EGFP plasmid was successfully constructed .Green fluorescence was observed in the HEK293 cells transfected with pcDNA3.0-HERG-EG-FP or cotransfected with pcDNA3.0-HERG and pcDNA3.1-PTPN11.The maximum densities of pulse and tail currents were significantly decreased in the PTPN11 overexpression group as compared with the control ([31.85 ±5.54] vs [45.92 ±3.18] pApF, P<0.05;[73.82 ±11.31] vs [108.43 ±7.98] pApF, P<0.05) but markedly in-creased in the PTPN11 overexpression with PAO group ([48.08 ±4.32] pApF;[120.06 ±8.02] pApF) (P<0.05).The time con-stant of deactivation was significantly higher in the PTPN 11 overexpression group than in the control ([622.16 ±46.49] vs [440.70 ± 49.49] ms, P<0.05). Conclusion The overexpression of PTPN11 decreases HERG potassium channel currents , which can be re-versed by PAO.This finding provides a theoretical basis for the application of certain regulatory enzymes in the HERG channel as a treat -ment of long QT syndrome .
ABSTRACT
Objective To study the effects of sibutramine on the human-ether-a-go-go-related gene (hERG) current in HEK293 cell line that overexpresses hERG potassium channels. Methods HEK293 cell line that overexpresses hERG potassium channels was constructed. Whole cell patch clamp techniques were employed to investigate the effects of sibutratime on Iherg in the cell line. Results Sibutramine reduced hERG current in a concentration-dependent manner:the inhibition rate was (8.82?2.32)%,(26.7?5.78)%,(44.93?4.60)% and (85.22?3.37)% at the dose of 3,10,30 and 100 ?mol/L. IC50 value was 32.66 ?mol/L (n=8). Ⅰ-Ⅴ relationship was inhibited by sibutramine (3,10,30 and 100 ?mol/L) at membrane potentials from -10 mV to +60 mV (step) and from 0 mV to +60 mV (tail) (n=8). Conclusion Sibutramine significantly inhibited Iherg in HEK293 cell line that overexpresses hERG potassium channels in a concentration-dependent manner,which may be a major mechanism of causing QT interval prolongation.