Inhibitory effect of tocainide on calcium current and potassium current in guinea pig ventricular myocytes
Wu, B.W.; Sheng, B.T.; Wang, W.Z.; Zhao, R.R.
Yao Xue Xue Bao 30(6): 412-416
1995
ISSN/ISBN: 0513-4870 PMID: 7572180 Document Number: 445188
In whole cell voltage clamp experiment, with isolated guinea pig ventricular myocytes, tocainide was shown to exhibit a concentration-dependent inhibition of calcium current (Ic-a) and delayed rectifier potassium current (I-K). Tocainide with a therapeutic concentration of 50 mu-mol cntdot L-1 significantly inhibited the I-Ca and I-tail (deactivating tail current of I-K) by 16% and 3% respectively. Inhibition of I-Ca by tocainide was also shown to be dependent upon stimulating frequencies, with a greater blockade occurring at 2.0 Hz (57%) than at 0.2 Hz (17%). Tocainide was found to inhibit the I-K,ATP by 74% at 200 mu-mol cntdot L-1 but not at 50 mu-mol cntdot L-1. These inhibitory effects on I-Ca and I-K can probably explain the therapeutic effect of tocainide on supraventricular tachycardia, and the shortening of plateau phase of action potential.