AIM To evaluate the
integration method for a nalysis of voltage-dependent Ca 2+-independent transient outward K+ cur rents
(I to) in pharmacology. METHODS The inactiva tion phases of I to were best fitted by the sum of two or thr ee exponentials equations. The area u nder the raw current curves (AUC) was obtained by the
integration of exponential equations. The AUC
normalized to the cell capacitance represented the net K+ charge flow during any depolarized duration and was as the index for comparison. Calcineurin overexpression transgenic (TG) mice showed downregulation of I to. These data were tested by the integration method. RESULTS AUC obtained from three or two exponentials fittings was calculated as: AUC=A 1τ 1+A 2τ 2+A 3τ 3+A 0t-A 1τ 1e - t/τ1-A 2τ 2e -t/τ2-A 3τ 3e -t/τ3 or AUC=A 1τ 1+A 2τ 2+A 0t- A 1τ 1e -t/τ1-A 2τ 2e -t/τ2. The 50% and 90% action potential duration (APD 50, APD 90) in ventricu lar myocytes of mice are about 10 ms and 30 ms, respectively. AUC at 10 ms (AUC 50, AUC of 50% APD) and 30 ms (AUC 90, AUC of 90% APD) in left ventricl e cardiomyocytes of wild type (WT) and TG mice were normalized to the cell capac itance. The normalized AUC 50 and AUC 90 of WT group were significantl y more than those of TG group, which was consistent to the prolongation of APD i n TG mice and the previous published results(downregulation of components of I to in TG mice). CONCLUSION The integration method was an ideal way for analysis of transient outward K+ currents in pharmacology.