Methylmercury induces Ca(2+)-dependent hyperpolarization of mouse thymocytes: a flow cytometric study using fluorescent dyes.
The effect of methylmercury on mouse thymocytes was examined using fluorescent dyes for membrane potential and intracellular Ca2+. Methylmercury at concentrations of 1 microM or higher (up to 30 microM) produced hyperpolarization in a dose-dependent fashion. Charybdotoxin and quinine, but not 4-aminopyridine and tetraethylammonium, greatly suppressed methylmercury-induced hyperpolarization. Removal of external Ca2+ reduced the degree of hyperpolarization. Pretreatment of thymocytes with A23187 under Ca(2+)-free conditions abolished the hyperpolarization induced by methylmercury. Under both normal and Ca(2+)-free conditions methylmercury increased the intracellular concentration of Ca2+. The results suggest that the increase in intracellular Ca2+ is mediated through a Ca2+ release from intracellular stores as well as through influx of external Ca2+. Therefore, it is likely that methylmercury increases the intracellular concentration of Ca2+, resulting in activation of Ca(2+)-dependent K+ conductance of mouse thymocytes.
Oyama
Y
Y
Laboratory of Cell Signaling Pharmacology, Graduate School of Human and Natural Environments, University of Tokushima, Japan.
Carpenter
D O
DO
Ueno
S
S
Hayashi
H
H
Tomiyoshi
F
F
D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D018999:Charybdotoxin / Q000494:pharmacology; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D008767:Methylmercury Compounds / Q000633:toxicity*; D051379:Mice; D008815:Mice, Inbred Strains; D010777:Photochemistry; D011803:Quinine / Q000494:pharmacology; D013601:T-Lymphocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*
D005456:Fluorescent Dyes; D008767:Methylmercury Compounds; D018999:Charybdotoxin; D011803:Quinine; D002118:Calcium