Zhang, Shetuan. Isolation and characterization of IKr in cardiac

doi:10.1152/ajpheart.00679.2005.—Isolation of the rapidly acti-vating delayed rectifier potassium current (IKr) from other cardiac currents has been a difficult task for quantitative study of this current. The present study was designed to separate IKr using Cs in cardiac myocytes. Cs have been known to block a variety of K channels, including many of those involved in the cardiac action potential such as inward rectifier potassium current IK1 and the transient outward potassium current Ito. However, under iso-tonic Cs conditions (135 mM Cs), a significant membrane current was recorded in isolated rabbit ventricular myocytes. This current displayed the voltage-dependent onset of and recovery from inactivation that are characteristic to IKr. Consistently, the current was selectively inhibited by the specific IKr blockers. The biophysical and pharmacological properties of the Cs-carried human ether-a-go-go-related gene (hERG) current were very sim