[Inhibitory effect of tocainide on calcium current and potassium current in guinea pig ventricular myocytes].
In whole cell voltage clamp experiment with isolated guinea pig ventricular myocytes, tocainide was shown to exhibit a concentration-dependent inhibition of calcium current (ICa) and delayed rectifier potassium current (IK). Tocainide with a therapeutic concentration of 50 mumol.L-1 significantly inhibited the ICa and Itail (deactivating tail current of IK) by 16% and 3% respectively. Inhibition of ICa 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 IK,ATP by 74% at 200 mumol.L-1 but not at 50 mumol.L-1. These inhibitory effects on ICa and IK can probably explain the therapeutic effect of tocainide on supraventricular tachycardia, and the shortening of plateau phase of action potential.
Wu
B W
BW
Department of Physiology, Shanxi Medical College, Taiyuan.
Sheng
B T
BT
Wang
W Z
WZ
Zhao
R R
RR
D000818:Animals; D015220:Calcium Channels / Q000187:drug effects*; D005260:Female; D006168:Guinea Pigs; D006352:Heart Ventricles; D066298:In Vitro Techniques; D008297:Male; D009206:Myocardium / Q000166:cytology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects*; D016677:Tocainide / Q000494:pharmacology*
D015220:Calcium Channels; D015221:Potassium Channels; D016677:Tocainide