Electrophysiological Effects Of No-antiarrhythmic Agents On Single Guinea Pig Ventricular Myocytes

Background Long QT syndrome (LQT) is a cardiovascular disease thatcauses syncope, seizure, and sudden death from cardiac arrhythmias, suchas torsade de pointes, and ventricular fibrillation. LQT can be inherited oracquired.Acquired LQT most frequently results from medications, oftenantiarrhythmic drugs, such as quinidine. There were also reports of LQT,even unexpected sudden cardiac death after the administrations ofpsychoactive drugs, macrolide antibiotics, or other no-antiarrhythmicagents.In order to understand the mechanisms of LQT induced by these no-antiarrhythmics drugs, we studied the effects of phenothiazine(psychoactive drug), bepridil (antianginal drug), erythromycin (antibiotics)on action potential duration (APD) and main currents involved in thedepolarization and repolarization of isolated guinea pig ventricularmyocytes.Methods and results Effects of the three drugs on APD of single guinea pig ventricular myocytes were studied by using Nystatin-perfortated configuration of the patch-clamp techniques. At a stimulation frequency of 5 Hz, phenothiazine (100 μmol/L) prolonged APD₉₀ by % (p<0.01), and the effect was reversible. Erythromycin also prolonged APD, but only at concentration of 300 μmol/L (APD₉₀ prolonged 11.89%, p<0.05), 100 μmol/L of erythromycin did not prolong the APD. 0.1 μmol/L bepridil prolonged APD₉₀ by 18.01% (p<0.05), but 1 μmol/L and 3 μmol/L bepridil did not change APD compared with that of control, while 10 μmol/L and 30 μmol/L...