Tityus zulianus venom induces massive catecholamine release from PC12 cells and in a mouse envenomation model

Abstract

Scorpion envenomation is a public health problem in Venezuela, mainly produced by Tityus discrepans (TD) and Tityus zulianus (TZ). Accidents by these two species differ clinically. Thus, TZ envenomation is associated with high mortality in children due to cardiopulmonary disorders, as a result of, excessive amounts of plasma catecholamines (Epinephrine) release from adrenal medulla, probably via the voltage-gated sodium-channel activated by specific scorpion toxins. This Epi release is, in part responsible, for some of the envenomation clinical consequences, resembling those described for patients presenting catecholamine-releasing tumors (pheochromocytoma). In this work, BALB/c mice and rat pheochromocytoma-derived PC12 cells were used to provide in vivo and in vitro models, respectively, on which the basis for the TZ-mediated catecholamine release mechanism could be elucidated. In mice, TZ venom increased, at 1h post-injection, the Epi plasma levels in 4000%, which remained elevated for 24h. A significant rise in plasma levels of the catecholamine catabolite 3-Methoxy-4-Hydroxy-Phenyl-Glycol (MHPG) was also observed. In [3H]dopamine-loaded PC12 cells, TZ venom potentiated the carbamylcholine (CC)-mediated release of [3H]dopamine, as shown by the leftward shift in the CC-dose-response curves. Moreover, TZ venom also displayed the maximal [3H]dopamine releasing activity compared to TD venom, with significant reduction of the EC50 for CC. The nicotinic-acetylcholine receptor (nAChR) blocker hexamethonium induced a significant inhibition of the [3H]dopamine release produced by CC in PC12 cells but the TZ-elicited release of [3H]dopamine was 70% hexamethonium-insensitive, suggesting unidentified TZ toxins affecting other regulatory mechanisms of catecholamine secretion.