Transient outward and delayed rectifier currents in canine atrium: Properties and role of isolation methods

Although the dog is the principal species used for in vivo studies of atrial arrhythmias, little is known about currents governing canine atrial repolarization. Cells were isolated from dog atria by exposure to collagenase of tissue in vitro (''chunk cells'') and by arterial perfusion (''perfusion cells''). Whole cell voltage clamp revealed transient outward K+ current (I-to1), Ca2+-dependent Cl- current (I-to2), and delayed rectifier K+ current (I-K). I-to1 recovered rapidly and showed little frequency dependence. Two components of I-K were present as follows: a rapidly activating E-4031-sensitive current with marked inward rectification and a slower-activating E-4031-insensitive component. I-to1 and I-K resembled corresponding currents previously described in human atrium. Transient outward currents were similar in chunk and perfusion cells, but I-K was seen in 4% of chunk cells vs. 99% of perfusion cells (P < 0.001). Suppression of each identified current retarded canine action potential repolarization. We conclude that I-to1, I-to2, and both components of I-K are present in dog atrium, I-K is much more sensitive to the isolation method than I-to1 or I-to2, and the properties of two important repolarizing currents (I-to1 and I-K) previously described in human atrium are similar to those in dog atrium.