Effect of yohimbine on action potentials recorded from isolated canine ventricular myocytes

Yohimbine is used extensively as an alpha 2-adrenoceptor antagonist. This drug also inhibits sodium channels in the squid axon. In this study we investigated the electrophysiological effects of yohimbine in isolated canine ventricular myocytes. Yohimbine produced a reversible and concentration-dependent decrease in the maximum upstroke velocity and a slight increase in the action potential duration. The maximum upstroke velocity was reduced by over 90% by 10(-4) M yohimbine. It did not effect the resting or plateau potentials in control or isoproterenol-treated cells. Delayed after-depolarizations were also inhibited. These data suggest that yohimbine can produce a local anesthetic effect which is primarily due to inhibition of sodium channels.