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First published online January 25, 2005
Journal of Experimental Biology 208, 523-537 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01417

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Cell volume control in Paramecium: factors that activate the control mechanisms

Masaaki Iwamoto^*, Kazuyuki Sugino, 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 (16K): [in a new window]   Fig. 1. The relationship between cell volume and the adaptation osmolarity in six different groups of Paramecium multimicronucleatum cells adapted to different osmolarities. Each plot for cell volume is the mean±S.D. (N=74–94) and is presented as a value relative to the mean volume of 84 mosmol l-1-adapted cells. A solid line is a binomial approximation of the plots.

View larger version (27K): [in a new window]   Fig. 2. Time courses of changes in cell volume after decreasing the external osmolarity by 60 mosmol l-1 in five different groups of P. multimicronucleatum adapted to different osmolarities. (A) 164 mosmol l-1-adapted cells were subjected to 104 mosmol l-1. (B) 144 mosmol l-1-adapted cells were subjected to 84 mosmol l-1. (C) 124 mosmol l-1-adapted cells were subjected to 64 mosmol l-1. (D) 84 mosmol l-1-adapted cells were subjected to 24 mosmol l-1. (E) 64 mosmol l-1-adapted cells were subjected to 4 mosmol l-1. Each plot for cell volume is the mean±S.D. (N=3) and presented as a value relative to the cell volume before decreasing the external osmolarity (at time 0).

View larger version (202K): [in a new window]   Fig. 4. Four sets of three consecutive pictures of a representative cell obtained from four different groups of P. multimicronucleatum cells adapted to different osmolarities taken at 0, 15 and 30 min, respectively, after changing the external osmolarity by 60 mosmol l-1. (A) A 144 mosmol l-1-adapted cell was subjected to 84 mosmol l-1. (B) A 84 mosmol l-1-adapted cell was subjected to 24 mosmol l-1. (C) A 4 mosmol l-1-adapted cell was subjected to 64 mosmol l-1. (D) A 64 mosmol l-1-adapted cell was subjected to 124 mosmol l-1. A white arrowhead points to an indentation of the cell. The top of each cell image corresponds to the anterior portion of the cell. A number in the upper left corner of each picture is the time in min after changing the external osmolarity when the picture was taken. Scale bar, 50 µm.

View larger version (27K): [in a new window]   Fig. 3. Time courses of changes in cell volume after increasing the external osmolarity by 60 mosmol l-1 in five different groups of P. multimicronucleatum adapted to different osmolarities. (A) 104 mosmol l-1-adapted cells were subjected to 164 mosmol l-1. (B) 84 mosmol l-1-adapted cells were subjected to 144 mosmol l-1. (C) 64 mosmol l-1-adapted cells were subjected to 124 mosmol l-1. (D) 24 mosmol l-1-adapted cells were subjected to 84 mosmol l-1. (E) 4 mosmol l-1-adapted cells were subjected to 64 mosmol l-1. Each plot for cell volume is the mean±S.D. (N=3) and presented as a value relative to the cell volume before increasing the external osmolarity (at time 0).

View larger version (25K): [in a new window]   Fig. 5. Effects of the degree of decrease in the external osmolarity on the time course of change in cell volume after decreasing the external osmolarity in P. multimicronucleatum. (A) Two groups of cells adapted to 144 mosmol l-1 were subjected to 84 mosmol l-1 (the degree of decrease; 60 mosmol l-1, gray open circles) or to 104 mosmol l-1 (the degree of decrease; 40 mosmol l-1, black open circles). (B) Three groups of cells adapted to 84 mosmol l-1 were subjected to 24 mosmol l-1 (the degree of decrease; 60 mosmol l-1, gray open circles), 44 mosmol l-1 (the degree of decrease; 40 mosmol l-1, black open circles) or 64 mosmol l-1 (the degree of decrease; 20 mosmol l-1, red open circles). Each plot for cell volume is the mean±S.D. (N=3) and presented as a value relative to the cell volume before decreasing the external osmolarity.

View larger version (26K): [in a new window]   Fig. 6. Effects of the degree of increase in the external osmolarity on the time course of change in cell volume after increasing the external osmolarity in P. multimicronucleatum. (A) Two groups of cells adapted to 4 mosmol l-1 were subjected to 64 mosmol l-1 (the degree of increase; 60 mosmol l-1, gray open circles) or to 44 mosmol l-1 (the degree of increase; 40 mosmol l-1; black open circles). (B) Three groups of cells adapted to 64 mosmol l-1 were subjected to 124 mosmol l-1 (the degree of increase; 60 mosmol l-1, gray open circles), 104 mosmol l-1 (the degree of increase; 40 mosmol l-1, red open circles) or 84 mosmol l-1 (the degree of increase; 20 mosmol l-1, black open circles). Each plot for cell volume is the mean±S.D. (N=3) and presented as a value relative to the cell volume before increasing the external osmolarity.

View larger version (41K): [in a new window]   Fig. 7. Effects of TEA+ and K+ in the external solution on the time course of change in cell volume after changing the external osmolarity in P. multimicronucleatum. (A) 164 mosmol l-1-adapted cells were transferred into a 10 mmol l-1 TEA+-containing 104 mosmol l-1 solution, (B) 164 mosmol l-1-adapted cells were transferred into a 30 mmol l-1 KCl-containing 104 mosmol l-1 solution. (C) 104 mosmol l-1-adapted cells were transferred into a 10 mmol l-1 164 mosmol l-1 TEA+-containing solution. (D) 104 mosmol l-1-adapted cells were transferred into a 30 mmol l-1 KCl-containing 164 mosmol l-1 solution. Each plot for cell volume is the mean±S.D. (N=3) and presented as a value relative to the cell volume before changing the external osmolarity.

View larger version (27K): [in a new window]   Fig. 8. Four representative time courses of change in the rate of fluid discharge from the contractile vacuole after changing the external osmolarity in P. multimicronucleatum. (A) A 164 mosmol l-1-adapted cell was subjected to 104 mosmol l-1. (B) A 144 mosmol l-1-adapted cell was subjected to 84 mosmol l-1. (C) A 104 mosmol l-1-adapted cell was subjected to 164 mosmol l-1. (D) A 84 mosmol l-1-adapted cell was subjected to 144 mosmol l-1.

View larger version (30K): [in a new window]   Fig. 9. (A) Estimated cytosolic osmolarity of P. multimicronucleatum as a function of the adaptation osmolarity. Light, medium and dark gray lines correspond to the cytosolic osmolarities for three different adaptation osmolarity ranges, i.e. less than (in mosmol l-1) 75, from 75 to 160 and more than 160, respectively. (B) A profile of changes in both adaptation osmolarity and osmolarity to which the adapted cells are subjected for 16 experiments done in the present study. 16 arrows correspond to these 16 different experiments, respectively. Light gray arrows, medium gray arrows and dark gray arrows correspond to the experiments with cells adapted to an osmolarity in an osmolarity range of less than 75 mosmol l-1, those with cells adapted to an osmolarity in an osmolarity range from 75 to 160 and those with cells adapted to an osmolarity in an osmolarity range of more than 160 mosmol l-1, respectively. Estimated cytosolic osmolarity of each cell is shown by a number under a line for the cytosolic osmolarity in A. Leftward arrows with a red asterisk beside each arrow are the cases where RVD takes place after cell's subjection to a decreased osmolarity. Rightward arrows with a blue asterisk beside each arrowhead show the cases where RVI takes place after cell's subjection to an increased osmolarity. Abscissa (external osmolarity) corresponds to the adaptation osmolarity for A and to both adaptation osmolarity and osmolarities to which the adapted cells are subjected for B. See the first paragraph of the Discussion section for more detail.

View larger version (48K): [in a new window]   Fig. 10. Values for cell volume, v(Cadp), (A), cytosolic osmolarity, Ccyt(Cadp), (B), cytosolic pressure, Pcyt(Cadp), (C) and the bulk modulus, MB(Cadp), (D), in P. multimicronucleatum cells plotted against the adaptation osmolarity, Cadp. Values for the natural cell volume, vN(Ccyt) (thick red lines), are plotted against the cytosolic osmolarity, Ccyt (red letters), instead of Cadp. A black filled circle labelled v(84) corresponds to volume of the cell adapted to 84 mosmol l-1 and all the cell volumes are presented as a percentage of v(84). Data on gray columns are estimated by extrapolation of the actual data for Cadp ranging from 4 to 204 mosmol l-1. Left gray column; for Cadp ranging from 0 to 4 mosmol l-1, right gray column; for Cadp ranging from 204 to 250 mosmol l-1. See the text for detail.