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First published online November 10, 2003

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Hypo-osmotic or Ca²⁺-rich external conditions trigger extra contractile vacuole complex generation in Paramecium multimicronucleatum

Masaaki Iwamoto, Richard D. Allen and Yutaka Naitoh^*

Pacific Biomedical Research Center, Snyder Hall 306, University of Hawaii at Manoa, 2538 The Mall, Honolulu, HI 96822, USA

View larger version (39K): [in a new window]   Fig. 1. (A) A frequency histogram for the number of cells containing different numbers (1-5) of CVCs obtained for two different populations of Paramecium multimicronucleatum cells. Black columns: cells cultured in a 84 mosmol l-1 axenic culture medium. White columns: cells adapted to a 4 mosmol l-1 standard saline solution. Values are means ± S.D. (N=3). (B) SS-1 labeling of the smooth spongiome, visualized by its immunological fluorescence image in cells adapted to a 4 mosmol l-1 standard saline solution for 24 h. (1) A cell with two CVCs. (2) A cell with three CVCs; an arrowhead indicates branching of a radial arm. (3) A cell with seven (maximum) CVCs. Scale bar, 50 µm.

View larger version (22K): [in a new window]   Fig. 2. A representative frequency histogram for the number of CVCs with different numbers of radial arms obtained for two different populations of P. multimicronucleatum cells. Black columns: cells cultured in a 84 mosmol l-1 axenic culture medium. White columns: cells adapted to a 4 mosmol l-1 standard saline solution.

View larger version (18K): [in a new window]   Fig. 3. The number of P. multimicronucleatum cells with extra CVCs as a function of the time after the cells were transferred from their 84 mosmol l-1 culture medium into three different saline solutions with different osmolarities (4, 64 and 144 mosmol l-1). The number is percentage of cells in each population of cells examined. Values are means ± S.D. (N=3).

View larger version (16K): [in a new window]   Fig. 4. The number of P. multimicronucleatum cells with extra CVCs as a function of the time after the cells were transferred from their 84 mosmol l-1 culture medium into different saline solutions with different ionic compositions but with the same overall osmolarity of 84 mosmol l-1. (A) The K+ concentrations were 5.0, 2.0 and 0.1 mmol l-1, respectively. (B) The Ca2+ concentrations were 1.0, 0.25, 0.1 and 0.001 mmol l-1, respectively. The number is percentage of cells in each population examined. Values are means ± S.D. (N=3).

View larger version (17K): [in a new window]   Fig. 5. The number of P. multimicronucleatum cells with extra CVCs (filled circles) and the cell density (open circles) as a function of the time after the cells were returned to their 84 mosmol l-1 axenic culture medium (at 0 time) from a 4 mosmol l-1 standard saline adaptation solution. The percentages of cells with extra CVCs were determined from 300 cells at each time selected at random. The cell density is the percentage compared to the density at -18 h, the time when the cells were transferred for adaptation into the standard saline solution from the axenic culture medium. Each symbol is the mean of two calculations obtained from two experimental series. Bars indicate ± S.D.

View larger version (104K): [in a new window]   Fig. 6. Generation of new CVCs in P. multimicronucleatum cells. Top of each photograph corresponds to the anterior end of the cell. (A) Normal generation in an axenic culture medium that precedes cell division. Each new CVC is generated anterior to each old CVC. (B) An extra CVC generated posterior to the posterior CVC. (C) An extra CVC generated by division of the anterior CVC. Scale bars, 20 µm.

View larger version (30K): [in a new window]   Fig. 7. Two sets of frequency histograms for the number of cells with different numbers (1-5) of CVCs (NCVC) obtained for two different populations of P. multimicronucleatum cells. (Left) Cells adapted to a 4 mosmol l-1 standard saline solution for 18 h (control). (Right) Cells adapted to a 4 mosmol l-1 standard saline solution containing 25 µmol l-1 aphidicolin for 18 h. Values are means ± S.D. (N=3).