title: Rapid downregulation of the Ca2+-signal after exocytosis stimulation in Paramecium cells: essential role of a centrin-rich filamentous cortical network, the infraciliary lattice.
abstract: We analysed in Paramecium tetraurelia cells the role of the infraciliary lattice, a cytoskeletal network containing numerous centrin isoforms tightly bound to large binding proteins, in the re-establishment of Ca2+ homeostasis following exocytosis stimulation. The wild type strain d4-2 has been compared with the mutant cell line Delta-PtCenBP1 which is devoid of the infraciliary lattice ("Delta-PtCenBP1" cells). Exocytosis is known to involve the mobilization of cortical Ca2+-stores and a superimposed Ca2+-influx and was analysed using Fura Red ratio imaging. No difference in the initial signal generation was found between wild type and Delta-PtCenBP1 cells. In contrast, decay time was greatly increased in Delta-PtCenBP1 cells particularly when stimulated, e.g., in presence of 1mM extracellular Ca2+, [Ca2+]o. Apparent halftimes of f/f0 decrease were 8.5 s in wild type and approximately 125 s in Delta-PtCenBP1 cells, requiring approximately 30 s and approximately 180 s, respectively, to re-establish intracellular [Ca2+] homeostasis. Lowering [Ca2+]o to 0.1 and 0.01 mM caused an acceleration of intracellular [Ca2+] decay to t(1/2)=33 s and 28 s, respectively, in Delta-PtCenBP1 cells as compared to 8.1 and 5.6, respectively, for wild type cells. We conclude that, in Paramecium cells, the infraciliary lattice is the most efficient endogenous Ca2+ buffering system allowing the rapid downregulation of Ca2+ signals after exocytosis stimulation.
authors.affiliation: Department of Biology, University of Konstanz, P.O. Box 5560, 78457 Konstanz, Germany.
authors.forename: Ivonne M
authors.initials: IM
authors.lastname: Sehring
authors.forename: Catherine
authors.initials: C
authors.lastname: Klotz
authors.forename: Janine
authors.initials: J
authors.lastname: Beisson
authors.forename: Helmut
authors.initials: H
authors.lastname: Plattner
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002458:Cell Fractionation; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000235:genetics / Q000502:physiology*; D003911:Dextrans / Q000494:pharmacology; D015536:Down-Regulation; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016805:Paramecium tetraurelia; D011485:Protein Binding; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D017384:Sequence Deletion; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000378:metabolism*
chemical_list: D003911:Dextrans; D008565:Membrane Proteins; C107339:ND7 protein, Protozoa; D015800:Protozoan Proteins; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; C039691:aminoethyldextran; D002118:Calcium