title: Calcium signaling in closely related protozoan groups (Alveolata): non-parasitic ciliates (Paramecium, Tetrahymena) vs. parasitic Apicomplexa (Plasmodium, Toxoplasma).
abstract: The importance of Ca2+-signaling for many subcellular processes is well established in higher eukaryotes, whereas information about protozoa is restricted. Recent genome analyses have stimulated such work also with Alveolates, such as ciliates (Paramecium, Tetrahymena) and their pathogenic close relatives, the Apicomplexa (Plasmodium, Toxoplasma). Here we compare Ca2+ signaling in the two closely related groups. Acidic Ca2+ stores have been characterized in detail in Apicomplexa, but hardly in ciliates. Two-pore channels engaged in Ca2+-release from acidic stores in higher eukaryotes have not been stingently characterized in either group. Both groups are endowed with plasma membrane- and endoplasmic reticulum-type Ca2+-ATPases (PMCA, SERCA), respectively. Only recently was it possible to identify in Paramecium a number of homologs of ryanodine and inositol 1,3,4-trisphosphate receptors (RyR, IP3R) and to localize them to widely different organelles participating in vesicle trafficking. For Apicomplexa, physiological experiments suggest the presence of related channels although their identity remains elusive. In Paramecium, IP3Rs are constitutively active in the contractile vacuole complex; RyR-related channels in alveolar sacs are activated during exocytosis stimulation, whereas in the parasites the homologous structure (inner membrane complex) may no longer function as a Ca2+ store. Scrutinized comparison of the two closely related protozoan phyla may stimulate further work and elucidate adaptation to parasitic life. See also "Conclusions" section.
authors.affiliation: Department of Biology, University of Konstanz, P.O. Box 5560, 78457 Konstanz, Germany. helmut.plattner@uni-konstanz.de
authors.forename: H
authors.initials: H
authors.lastname: Plattner
authors.forename: I M
authors.initials: IM
authors.lastname: Sehring
authors.forename: I K
authors.initials: IK
authors.lastname: Mohamed
authors.forename: K
authors.initials: K
authors.lastname: Miranda
authors.forename: W
authors.initials: W
authors.lastname: De Souza
authors.forename: R
authors.initials: R
authors.lastname: Billington
authors.forename: A
authors.initials: A
authors.lastname: Genazzani
authors.forename: E-M
authors.initials: EM
authors.lastname: Ladenburger
mesh_terms: D056893:Alveolata / Q000502:physiology; D000818:Animals; D005075:Biological Evolution; D002118:Calcium / Q000737:chemistry / Q000378:metabolism*; D020013:Calcium Signaling / Q000502:physiology*; D016678:Genome; D007295:Inositol Phosphates / Q000235:genetics / Q000502:physiology*; D010247:Paramecium / Q000502:physiology; D053499:Plasma Membrane Calcium-Transporting ATPases / Q000235:genetics / Q000502:physiology*; D010961:Plasmodium / Q000502:physiology; D019837:Ryanodine Receptor Calcium Release Channel / Q000235:genetics / Q000502:physiology*; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000235:genetics / Q000378:metabolism
chemical_list: D007295:Inositol Phosphates; D019837:Ryanodine Receptor Calcium Release Channel; C058097:inositol 1,3,4-trisphosphate; D053499:Plasma Membrane Calcium-Transporting ATPases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D002118:Calcium