Selective release of ATP from sympathetic nerves of rat vas deferens by the toxin TsTX-I from Brazilian scorpion Tityus serrulatus

1 The effects of the main component of the Tityus serrulatus scorpion venom, toxin TsTX-I, were studied on the contractility and release of neurotransmitters in the rat vas deferens. Since TsTX-I is known to act on sodium channels, we used veratridine, another sodium channel agent, for comparison. 2 Toxin TsTX-I induced concentration-dependent contractions with an EC50 value of 47.8+/-0.1 nM and a maximum effect of 84.4+/-10.4% of that for BaCl2. 3 Contractions by TsTX-I were abolished by denervation or tetrodotoxin (0.1 muM), showing that the toxin effects depend on the integrity of sympathetic nerve terminals. 4 To check for the presence of a noradrenergic component, experiments were conducted after removal of adrenergic stores in nerve terminals by reserpinization (10 mg kg(-1), 24 h prior to experiments) or blockade of alpha(1) adrenoceptors by prazosin (30 muM), showing that these procedures did not modify the response to TsTX-I, and therefore that adrenoceptors were not involved in contractions. 5 To check for the presence of a purinergic component, experiments were carried out after blockade of P-2X receptors by suramin (0.1 mM) or desensitization by alpha,beta-methylene-ATP (30 muM). These agents greatly abolished the contractile response to TsTX-I (about 83% by desensitization and 96% by suramin), showing the involvement of purinergic receptors. 6 The release of noradrenaline and purinergic agents (ATP, ADP, AMP and adenosine) was detected by HPLC. Together, the total release of purines in the presence of TsTX-I was about 42 times higher than in the control group. In contrast, TsTX-I did not modify the overflow of noradrenaline, showing that the release was selective for purines. 7 The release of purinergic agents was reduced by the N-type calcium channel blocker omega-conotoxin GVIA (1 muM) and by the P/Q-type blocker omega-conotoxin MVIIC (1 muM), showing that the effects of TsTX-I are calcium-dependent. 8 The results show that TsTX-I produced a selective release of purines from postganglionic sympathetic nerves in the rat vas deferens.