Effects Induced by Tityus serrulatus Scorpion Venom and Its Toxins TsTX-I and TsTX-V on the Rat Isolated Retractor Penis Muscle

The aims of the present study were to investigate the pharmacological effects induced by Tityus serrulatus venom (TsV) and its fractions and to compare with the effects induced by pure α (TsTX-V) and β (TsTX-I) toxins isolated from TsV on rat retractor penis muscle (RPM). TsV, fractions X, XI, XIIa, XIIb (0.01–100 µg/ml) and TsTX-V (1 nmol/l–10 µmol/l) induced concentration-dependent contractions. Prazosin and guanethidine or tetrodotoxin (TTX, 5 µmol/l, 30 min) completely abolished these contractions, suggesting complete dependence on sympathetic nerves. TsV or fractions X, XI, XIIa, XIIb (0.01– 100 µg/ml), TsTX-I and TsTX-V (1 nmol/l–10 µmol/l) induced concentration-dependent relaxations in the precontracted RPM. TTX or N ω -nitro-L-arginine methyl ester (L-NAME, 100 µmol/l, 30 min) completely abolished the relaxations. Our results suggest that most of TsV-derivated toxins induce contraction and relaxation on RPM by sympathetic and NANC nitrergic nerve stimulation. Noteworthy, TsTX-I only induces relaxation on RPM suggesting that this protein selectively acts on inhibitory nerves.