Journal Article

Characterization of Calcium Oscillations in Normal and Benzo[<i>a</i>]pyrene-Treated Clone 9 Cells

Rola Barhoumi, Youssef Mouneimne, Igbal Awooda, Stephen H. Safe, Kirby C. Donnelly and Robert C. Burghardt

in Toxicological Sciences

Volume 68, issue 2, pages 444-450
Published in print August 2002 | ISSN: 1096-6080
Published online August 2002 | e-ISSN: 1096-0929 | DOI: http://dx.doi.org/10.1093/toxsci/68.2.444
Characterization of Calcium Oscillations in Normal and Benzo[a]pyrene-Treated Clone 9 Cells

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Intracellular Ca2+ oscillations induced by oxytocin and vasopressin were analyzed in a rat liver cell line (Clone 9) in order to identify mechanisms by which benzo[a]pyrene (BaP) alters Ca2+signaling patterns in these cells. Clone 9 cells exhibit an initial Ca2+ spike, followed by Ca2+ oscillations upon oxytocin or vasopressin treatment. The range of frequencies (maximum 110 mHz) was dependent on agonist concentration with a constant amplitude less than or equal to the amount of Ca2+ generated from the inositol trisphosphate (InsP3)-sensitive pool. This study examined contributions of extracellular and intracellular pools to the frequency of Ca2+ oscillations and the role of membrane channels, second messengers, and different pharmacological reagents on the regulation of oscillation frequency in both control and BaP-treated cells. Results indicated that the Ca2+ oscillations are mainly due to inositol 1,4,5-triphosphate (InsP3)-sensitive stores and that extracellular Ca2+ contributes to refilling of this intracellular Ca2+ pool. The frequency of Ca2+ oscillations is also sharply affected by protein kinase C activated by phospholipase C. In BaP-treated Clone 9 cells, basal Ca2+ levels were elevated and the frequency of Ca2+ oscillations was suppressed in a dose-dependent fashion. Suppression of Ca2+ oscillations is due, at least in part, to an effect of BaP on enhanced opening of K+ channels. This was confirmed by showing that inhibition of the K+ channel opening by tetraethylammonium chloride can reverse the effect of BaP on oxytocin-induced Ca2+ oscillations, and potentially decrease the toxicity of BaP.

Keywords: Ca2+ oscillations; oxytocin; vasopressin; fluorescence microscopy; laser cytometry; BaP

Journal Article.  5412 words.  Illustrated.

Subjects: Medical Toxicology ; Toxicology (Non-medical)

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