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

Eva-Maria Ladenburger, Iris Korn, Nicole Kasielke, Thomas Wassmer, Helmut Plattner

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Pages (from-to)3705-3717
Number of pages13
JournalJournal of Cell Science
Issue number17
Early online date15 Aug 2006
Publication statusPublished - 1 Sept 2006

Bibliographical note

© The Company of Biologists Limited 2006


  • Ca2+
  • IP3
  • calcium
  • inositol 1,4,5-trisphosphate
  • osmoregulation
  • paramecium


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