Effects of toxin Ts-γ and tityustoxin purified from Tityus serrulatus scorpion venom on isolated rat atria

Abstract

The effects of toxin Ts-γ and tityustoxin purified from Tityus serrulatus scorpion venom were investigated on isolated rat atria. Rat atria were placed in an organ bath containing Krebs-Ringer solution, 30 °C, pH 7.4, and bubbled with a gas mixture of 95% O 2 and 5% CO 2. The atrial rate and contractile force were simultaneously recorded. Addition of toxin Ts-γ to the bath (0.14 μM) evoked an initial reduction of both atrial rate and contractile force, followed by a small increase in force and a decrease in rate, and finally a long reduction of rate and force. Addition of an identical dose of Ts-γ 30 or 60 min later did not evoke any effect. Addition of tityustoxin to the bath (0.14 μM) induced an increase of atrial rate and force. Addition of an identical dose of tityustoxin 30 min later evoked similar effects. The negative chronotropic and inotropic effects induced by Ts-γ were abolished by tetrodotoxin (TTX, 1 μM) or atropine (1.5 μM), whereas the positive effects observed in the presence of atropine were prevented by TTX (1 μM) or alprenolol (10 μM). The negative chronotropic effect of 0.14 μM tityustoxin was only observed in the presence of physostigmine (0.3 μM). This negative effect was abolished by TTX (1 μM) or atropine (1.5 μM). The positive inotropic effect of tityustoxin was decreased by TTX (1 μM and 10 μM), but was totally prevented by guanethidine (10 μM) or alprenolol (10 μM). It is concluded that the main effects of toxin Ts-γ on isolated rat atria are on cholinergic nerve fibers and of long duration, whereas the main effects of tityustoxin are on adrenergic nerve fibers and of short duration.