Alteration of intracellular Ca²⁺ homeostasis and membrane potential by low dose hydroxylated PCB in PC12 cells.

Abstract

Polychlorinated biphenyls (PCBs) are well known pollutants that persist ubiquitously in the environment at low concentration. Some of their congeners may affect neuronal development and function by altering signal transduction and gene expression. However, the molecular mechanisms underlying their neurotoxicity are still not clear. Since Ca²⁺ is used as an intracellular signaling molecule, we investigated whether PCB alters Ca²⁺ oscillation in PC12 cells. We also analyzed the effect of PCB on membrane potential, since the alteration of Ca²⁺ oscillation is often associated with its changes.PC12 cells were loaded with Fura-2 AM for Ca²⁺ oscillation and DiBAC₄(3) for membrane potential. PCB (4(OH)-2',3,3',4',5'-penta CB, OH-PCB) was added to the medium at a final concentration of 10⁻⁸ M. Fluorescence of Fura-2 and DiBAC₄(3) was monitored using a CCD camera.Exposure to OH-PCB increased the intracellular Ca²⁺ content up to 3 times. The rise was gradual starting right after the PCB treatment. Interestingly, the increase in intracellular Ca²⁺ preceded the plasma membrane depolarization. Membrane potential showed an increase of 6 times in average with a delay of 1 to 2 min after application of PCB. Deprivation of extracellular Ca²⁺ reduced significantly the increase in cytoplasmic Ca²⁺ after OH-PCB treatment. Our results indicate that low-dose OH-PCBs alter membrane potential as well as disrupt Ca²⁺ homeostasis in part by inducing extracellular Ca²⁺ influx. These mechanisms may partly mediate its toxicity. [J Physiol Sci. 2007;57 Suppl:S122]