Characterization of calcium oscillations in normal and benzo[a]pyrene-treated clone 9 cells.
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 (InsP(3))-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 (InsP(3))-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.
Barhoumi
Rola
R
Department of Veterinary Anatomy and Public Health, Texas A&M University, College Station, Texas 77843, USA.
Mouneimne
Youssef
Y
Awooda
Igbal
I
Safe
Stephen H
SH
Donnelly
Kirby C
KC
Burghardt
Robert C
RC
D000818:Animals; D001564:Benzo(a)pyrene / Q000633:toxicity*; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002273:Carcinogens / Q000633:toxicity*; D002460:Cell Line; D002999:Clone Cells; D004336:Drug Antagonism; D019044:Image Cytometry; D008099:Liver / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D010121:Oxytocin / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000494:pharmacology; D051381:Rats; D019789:Tetraethylammonium / Q000494:pharmacology; D014667:Vasopressins / Q000494:pharmacology
D002273:Carcinogens; D026902:Potassium Channel Blockers; D014667:Vasopressins; D001564:Benzo(a)pyrene; D010121:Oxytocin; D019789:Tetraethylammonium; D002118:Calcium