Effect of tributyltin chloride on the release of calcium ion from intracellular calcium stores in rat hepatocytes

Citation
T. Kawanishi et al., Effect of tributyltin chloride on the release of calcium ion from intracellular calcium stores in rat hepatocytes, BIOCH PHARM, 62(7), 2001, pp. 863-872
Citations number
42
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Pharmacology & Toxicology
Journal title
BIOCHEMICAL PHARMACOLOGY
ISSN journal
0006-2952 → ACNP
Volume
62
Issue
7
Year of publication
2001
Pages
863 - 872
Database
ISI
SICI code
0006-2952(20011001)62:7<863:EOTCOT>2.0.ZU;2-L
Abstract
The effects of tri-n-butyltin chloride (TBT), an environmental pollutant, o n the release of Ca2+ from intracellular stores were investigated in isolat ed rat hepatocytes. Isolated hepatocytes permeabilized with digitonin were suspended in solution, and the concentration of extracellular Ca2+ was meas ured, using a fluorescent Ca2+ dye, fura-2. In the solution containing perm eabilized hepatocytes that had been preincubated with 4.0 muM TBT for 30 mi n, the extracellular Ca2+ concentration was high, but the inositol 1,4,5-tr isphosphate (InsP(3))-induced increase in Ca2+ concentration was suppressed , suggesting that the extracellular release of Ca2+ in response to TBT trea tment was from intracellular stores. Images of the Ca2+ concentration in th e intracellular stores of primary cultured hepatocytes loaded with fura-2 w ere obtained after digitonin-permeabilization, using digitalized fluorescen ce microscopy. The permeabilized hepatocytes that had been preincubated wit h 4.0 muM TBT for 30 min had a very low fura-2 fluorescence ratio (340/380 nm), suggesting that stored Ca2+ was released. When the hepatocytes were tr eated with 4.0 muM TBT after digitonin-permeabilization, the decrease in th e fura-2 fluorescence ratio was very small. However, when the permeabilized hepatocytes were incubated with 4.0 muM TBT and 2.0 muM NADPH, the decreas e was enhanced, raising the possibility that TBT might be metabolized to th e active form(s), thus releasing Ca2+ from intracellular stores. When the h epatocytes were preincubated with 0.1 muM TBT for 30 min and then were perm eabilized, the fura-2 fluorescence ratio was almost the same as that in the control permeabilized hepatocytes. However, the InsP(3)-induced decrease i n the fluorescence ratio was suppressed significantly in the permeabilized hepatocytes. These results suggest that TBT released Ca2+ from the intracel lular stores at high concentrations, and suppressed the InsP(3)-induced Ca2 + release at non-toxic low concentrations. It is probable that the latter e ffect was responsible for the previously reported suppression of Ca2+ respo nse induced by hormonal stimulations (Kawanish et al., Toxicol Appl Pharmac ol 1999; 155:54-61). (C) 2001 Elsevier Science Inc. All rights reserved.