Cortical Alveoli of Paramecium: A Vast Submembranous Calcium Storage Compartment

The plasma membrane of Paramecium is underlain by a continuous layer of membrane vesicles known as cortical alveoli, whose function was unknown but whose organization had suggested some resemblance with muscle sarcoplasmic reticulum. The occurrence of antimonate precipitates within the alveoli first...

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Bibliographic Details
Published in:The Journal of cell biology 1991-04, Vol.113 (1), p.103-112
Main Authors: Stelly, Nicole, Mauger, Jean-Pierre, Claret, Michel, Adoutte, André
Format: Article
Language:English
Subjects:
Adenosine triphosphatases
Animals
Biochemistry. Physiology. Immunology. Molecular biology
Biological and medical sciences
Biological Transport, Active - drug effects
Calcium
Calcium - metabolism
Calcium Channels - physiology
Calcium-Transporting ATPases - metabolism
Calmodulin - physiology
Cell Compartmentation
Cell Fractionation
Cell membranes
Cells
Cilia
Exocytosis
Fundamental and applied biological sciences. Psychology
Gels
Histocytochemistry
Intracellular Membranes - physiology
membrane vesicles
Microscopy, Electron
Organelles
Paramecium - metabolism
Paramecium - physiology
Paramecium - ultrastructure
Physiological regulation
Povidone
Protozoa
Pumps
Silicon Dioxide
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Summary:The plasma membrane of Paramecium is underlain by a continuous layer of membrane vesicles known as cortical alveoli, whose function was unknown but whose organization had suggested some resemblance with muscle sarcoplasmic reticulum. The occurrence of antimonate precipitates within the alveoli first indicated to us that they may indeed correspond to a vast calcium storage site. To analyze the possible involvement of this compartment in calcium sequestration more directly, we have developed a new fractionation method, involving a Percoll gradient, that allows rapid purification of the surface layer (cortex) of Paramecium in good yield and purity and in which the alveoli retain their in vivo topological orientation. This fraction pumped calcium very actively in a closed membrane compartment, with strict dependence on ATP and Mg2+. The pumping activity was affected by anti-calmodulin drugs but no Triton-soluble calmodulin binding protein could be identified, using gel overlay procedures. The high affinity of the pump for calcium (K m=0.5 μM) suggests that it plays an important role in the normal physiological environment of the cytosol. This may be related to at least three calcium-regulated processes that take place in the immediate vicinity of alveoli: trichocyst exocytosis, ciliary beating and cytoskeletal elements dynamics during division.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.113.1.103