Dual actions of lindane (γ-hexachlorocyclohexane) on calcium homeostasis and exocytosis in rat PC12 cells

The persistent organochlorine pesticide lindane is still abundantly found in the environment and in human and animal tissue samples. Lindane induces a wide range of adverse health effects, which are at least partially mediated via the known inhibition of GABAA and glycine receptors. Additionally, lindane has been reported to increase the basal intracellular Ca2+ concentration ([Ca2+]i). As Ca2+ triggers many cellular processes, including cell death and vesicular neurotransmitter release (exocytosis), we investigated whether lindane affects exocytosis, Ca2+ homeostasis, production of reactive oxygen species (ROS) and cytotoxicity in neuroendocrine PC12 cells. Amperometric recordings and [Ca2+]i imaging experiments with fura-2 demonstrated that lindane (≥ 10 μM) rapidly increases basal exocytosis and basal [Ca2+]i. Additional imaging and electrophysiological recordings revealed that this increase was largely due to a lindane-induced membrane depolarization and subsequent opening of N- and P/Q-type voltage-gated Ca2+ channels (VGCC). On the other hand, lindane (≥ 3 μM) induced a concentration-dependent but non-specific inhibition of VGCCs, thereby limiting the lindane-induced increase in basal [Ca2+]i and exocytosis. Importantly, the non-specific inhibition of VGCCs also reduced stimulation-evoked exocytosis and Ca2+ influx. Though lindane exposure concentration-dependently increased ROS production, cell viability was not affected indicating that the used concentrations were not acute cytotoxic.These combined findings indicate that lindane has two, partly counteracting effects. Lindane causes membrane depolarization, thereby increasing basal [Ca2+]i and exocytosis. In parallel, lindane inhibits VGCCs, thereby limiting the basal effects and reducing stimulation-evoked [Ca2+]i and exocytosis. This study further underlines the need to consider presynaptic, non-receptor-mediated effects in human risk assessment.