Characteristics of transient outward K+ current in human atrial cardiomyocytes.

AIM: To study the properties of transient outward potassium current (Ito) in human atrial myocytes. METHODS: The patch-clamp whole-cell recording techniques were used. When the calcium inward current was blocked by CdCl2 (0.1 mmol.L-1), the transient outward potassium current (Ito) was recorded by depolarizing cells. RESULTS: The current was voltage dependent, it was activated quickly and inactivated rapidly too. 4-Aminopyridine (4-AP) 10 mmol.L-1 (a selective blocker of Ito) blocked the current completely. The IC50 (95% confidence limits) of 4-AP on Ito were 0.67 (0.58-0.80) mmol.L-1, 4-AP 1 mmol.L-1 shifted the activation curve of Ito to positive potential, therefore a higher membrane potential was required to activate Ito. CONCLUSION: Ito, a major K+ channel current in human atrial cells, is blocked by 4-AP.