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ArticlesCopyright © 1988 by American Association for the Advancement of Science
Inositol 1,3,4,5-tetrakisphosphate induces Ca2+ sequestration in rat liver cells
Cancer Research Center of Hawaii, University of Hawaii, Honolulu 96813.
Inositol 1,4,5-trisphosphate [I(1,4,5)P3] is a second messenger generated along with diacylglycerol upon the binding of various physiological agents with their cell surface receptors. I(1,4,5)P3 mobilizes Ca2+ from intracellular storage sites through a receptor-coupled mechanism, and the subsequent increased intracellular free calcium ion concentration [( Ca2+]i) activates a multitude of cellular responses. Electropermeabilized neoplastic rat liver epithelial (261B) cells were used to study Ca2+ sequestration, a process that reverses the elevated [Ca2+]i to resting levels and replenishes intracellular Ca2+ pools. Although I (1,4,5)P3-mobilized Ca2+ is readily sequestered into storage pools by the action of Ca2+-adenosine triphosphatases, Ca2+ mobilized by addition of the nonmetabolized inositol trisphosphate isomer I(2,4,5)P3 is not sequestered, suggesting that metabolism is necessary to eliminate the stimulus for Ca2+ release. Several inositol phosphate compounds were examined for their ability to lower the buffer [Ca2+] to determine if a specific I(1,4,5)P3 metabolite might be involved in stimulating Ca2+ sequestration; of these, I(1,3,4,5)P4 alone was found to induce Ca2+ sequestration, demonstrating a physiological role for this inositol trisphosphate metabolite.
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Science. ISSN 0036-8075 (print), 1095-9203 (online)