An Ins(1,4,5)P3 receptor in Paramecium is associated with the osmoregulatory system


In the ciliate Paramecium, a variety of well characterized processes are regulated by Ca2+, e.g. exocytosis, endocytosis and ciliary beat. Therefore, among protozoa, Paramecium is considered a model organism for Ca2+ signaling, although the molecular identity of the channels responsible for the Ca2+ signals remains largely unknown. We have cloned - for the first time in a protozoan - the full sequence of the gene encoding a putative inositol (1,4,5)-trisphosphate (Ins(1,4,5)P3) receptor from Paramecium tetraurelia cells showing molecular characteristics of higher eukaryotic cells. The homologously expressed Ins(1,4,5)P3-binding domain binds [3H]Ins(1,4,5)P3, whereas antibodies unexpectedly localize this protein to the osmoregulatory system. The level of Ins(1,4,5)P3-receptor expression was reduced, as shown on a transcriptional level and by immuno-staining, by decreasing the concentration of extracellular Ca2+ (Paramecium cells rapidly adjust their Ca2+ level to that in the outside medium). Fluorochromes reveal spontaneous fluctuations in cytosolic Ca2+ levels along the osmoregulatory system and these signals change upon activation of caged Ins(1,4,5)P3. Considering the ongoing expulsion of substantial amounts of Ca2+ by the osmoregulatory system, we propose here that Ins(1,4,5)P3 receptors serve a new function, i.e. a latent, graded reflux of Ca2+ to fine-tune [Ca2+] homeostasis.

Publication DOI:
Divisions: Life & Health Sciences > Biosciences
Life & Health Sciences
Life & Health Sciences > Cellular and Molecular Biomedicine
Additional Information: © The Company of Biologists Limited 2006
Uncontrolled Keywords: Ca2+,IP3,calcium,inositol 1,4,5-trisphosphate,osmoregulation,paramecium
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Related URLs: http://jcs.biol ... ent/119/17/3705 (Publisher URL)
PURE Output Type: Article
Published Date: 2006-09-01
Published Online Date: 2006-08-15
Authors: Ladenburger, Eva-Maria
Korn, Iris
Kasielke, Nicole
Wassmer, Thomas
Plattner, Helmut



Version: Published Version

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