Effects of fire ant venom alkaloids on platelet and neutrophil function

About 95% of venom of the imported fire ant Solenopsis invicta is composed of dialkyl piperidines. These alkaloids produce a distinct pustule at the site of injection. The formation of this pustule may involve the activation of platelets and neutrophils. The purpose of this paper was to characterize the effects of fire ant venom alkaloids (FAVA) on certain physiological and biochemical functions of human platelets and neutrophils. In platelets, FAVA caused a rise in intracellular [Ca2+], secretion of dense granules as measured by ATP release, and aggregation as measured by light transmission through a suspension of platelets. Aggregation response was less complete with FAVA than with thrombin or PAF. However, secretion response was greater with FAVA than thrombin. One of our most significant findings was that pretreatment of platelets with subthreshold concentrations of FAVA produced enhanced PAF-induced increase in [Ca2+]cyt, suggesting that synergism between the two agonists might play an important role in the physiological response to FAVA. In neutrophils, FAVA produced a rise in intracellular [Ca2+] and aggregation, although the responses were more moderate than those observed in platelets. These results suggest that FAVA activation of platelets and neutrophils may occur in vivo as a response to stings by red fire ants.