Membrane hyperpolarization and depolarization of rat thymocytes by azoxystrobin, a post harvest fungicide

Azoxystrobin, a broad-spectrum fungicide, has been increasingly used in the agricultural industry. In Japan in 2018, azoxystrobin at five times the normal limit was detected in a shipment of Australian barley that had been used in food products. Therefore, the effects of azoxystrobin need to be carefully examined to predict potential adverse reactions in humans. In this study, the effects of azoxystrobin on the membrane potential and intracellular Ca²⁺ levels of thymocytes have been photochemically examined using flow cytometry. Azoxystrobin hyperpolarized plasma membrane potential. This hyperpolarization appeared to be due to the activation of Ca²⁺-dependent K⁺ channels, as both the removal of extracellular Ca²⁺ and addition of charybdotoxin attenuated the observed hyperpolarization. In the presence of quinine, an anti-malarial drug that blocks Ca²⁺-dependent K⁺ channels, azoxystrobin depolarized the membranes instead. Azoxystrobin increased intracellular Ca²⁺ levels in a concentration-dependent manner through the influx of extracellular Ca²⁺ and intracellular release of Ca²⁺, as confirmed by reduction in azoxystrobin-induced response in the absence of extracellular Ca²⁺. It appears likely that azoxystrobin at micromolar concentrations modifies membrane ion permeability in thymocytes. Since changes in membrane potential and intracellular Ca²⁺ levels occur during typical physiological lymphocyte responses, azoxystrobin may disturb lymphocyte function.