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 GABA(A) and glycine receptors. Additionally, lindane has been reported to increase the basal intracellular Ca(2+) concentration ([Ca(2+)](i)). As Ca(2+) triggers many cellular processes, including cell death and vesicular neurotransmitter release (exocytosis), we investigated whether lindane affects exocytosis, Ca(2+) homeostasis, production of reactive oxygen species (ROS) and cytotoxicity in neuroendocrine PC12 cells. Amperometric recordings and [Ca(2+)](i) imaging experiments with fura-2 demonstrated that lindane (≥ 10 μM) rapidly increases basal exocytosis and basal [Ca(2+)](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 Ca(2+) 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 [Ca(2+)](i) and exocytosis. Importantly, the non-specific inhibition of VGCCs also reduced stimulation-evoked exocytosis and Ca(2+) 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 [Ca(2+)](i) and exocytosis. In parallel, lindane inhibits VGCCs, thereby limiting the basal effects and reducing stimulation-evoked [Ca(2+)](i) and exocytosis. This study further underlines the need to consider presynaptic, non-receptor-mediated effects in human risk assessment.
Heusinkveld
Harm J
HJ
Neurotoxicology Research Group, Institute for Risk Assessment Sciences (IRAS), Utrecht University, P.O. Box 80.177, NL-3508 TD Utrecht, The Netherlands. H.J.Heusinkveld@uu.nl
Thomas
Gareth O
GO
Lamot
Ischa
I
van den Berg
Martin
M
Kroese
Alfons B A
AB
Westerink
Remco H S
RH
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020864:Calcium Channels, N-Type / Q000187:drug effects / Q000378:metabolism; D020865:Calcium Channels, P-Type / Q000187:drug effects / Q000378:metabolism; D020907:Calcium Channels, Q-Type / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology; D005089:Exocytosis / Q000187:drug effects*; D001556:Hexachlorocyclohexane / Q000008:administration & dosage / Q000633:toxicity*; D006706:Homeostasis / Q000187:drug effects; D007306:Insecticides / Q000008:administration & dosage / Q000633:toxicity*; D016716:PC12 Cells; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism
D020864:Calcium Channels, N-Type; D020865:Calcium Channels, P-Type; D020907:Calcium Channels, Q-Type; D007306:Insecticides; D017382:Reactive Oxygen Species; D001556:Hexachlorocyclohexane; D002118:Calcium