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Journal of Experimental Biology, Vol 201, Issue 3 451-460, Copyright © 1998 by Company of Biologists
JOURNAL ARTICLES |
T. Tominaga, R. D. Allen and R. Naitoh
In the freshwater protozoan Paramecium multomicronucleatum, excess cytosolic water, acquired osmotically, is segregated and expelled to the cell exterior through the activity of the contractile vacuole complex. This process keeps the cell volume constant. The electrophysiological parameters of the organelle were measured in situ using a fine-tipped microelectrode inserted into the contractile vacuole, the exocytotic vesicle of the organelle to which the segregated fluid is transported before being expelled to the exterior. The input capacitance decreased markedly immediately before fluid expulsion and regained its previous value when fluid filling resumed after fluid expulsion. This change in the capacitance proved that the contractile vacuole became disconnected from its radial arms, which project from the vacuole, before fluid expulsion occurred and then reconnected with the arms after fluid expulsion. A positive electrical potential was recorded from the contractile vacuole only when it was connected to the radial arms. This implies that the electrogenic mechanism resides exclusively in the radial arms and supports the idea that the decorated spongiomes, V-type proton-pump-covered terminal tubules of the radial arms that end blindly in the cytosol, are electrogenic. The linear current-voltage relationship of the contractile vacuole membrane also implies that few voltage-activated ion channels are present in the membrane. To explain the movement of water into the contractile vacuole complex, we favour the hypothesis that the potential generated across the decorated spongiome membrane can be used to drive counter-anions from the cytosol into the lumen of the complex. The anions could then act as an osmolite to pull cytosolic water into the lumen of the organelle.
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 K. Sugino, T. Tominaga, R. D. Allen, and Y. Naitoh Electrical properties and fusion dynamics of in vitro membrane vesicles derived from separate parts of the contractile vacuole complex of Paramecium multimicronucleatum J. Exp. Biol., October 15, 2005; 208(20): 3957 - 3969. [Abstract] [Full Text] [PDF]
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R. Kissmehl, M. Froissard, H. Plattner, M. Momayezi, and J. Cohen NSF regulates membrane traffic along multiple pathways in Paramecium J. Cell Sci., October 15, 2002; 115(20): 3935 - 3946. [Abstract] [Full Text] [PDF]
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H. K. Gronlien, C. Stock, M. S. Aihara, R. D. Allen, and Y. Naitoh Relationship between the membrane potential of the contractile vacuole complex and its osmoregulatory activity in Paramecium multimicronucleatum J. Exp. Biol., October 15, 2002; 205(20): 3261 - 3270. [Abstract] [Full Text] [PDF]
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C. Stock, H. K. Gronlien, R. D. Allen, and Y. Naitoh Osmoregulation in Paramecium: in situ ion gradients permit water to cascade through the cytosol to the contractile vacuole J. Cell Sci., January 6, 2002; 115(11): 2339 - 2348. [Abstract] [Full Text] [PDF]
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T Tani, R. Allen, and Y Naitoh Cellular membranes that undergo cyclic changes in tension: Direct measurement of force generation by an in vitro contractile vacuole of Paramecium multimicronucleatum J. Cell Sci., January 2, 2001; 114(4): 785 - 795. [Abstract] [PDF]
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T Tani, R. Allen, and Y Naitoh Periodic tension development in the membrane of the in vitro contractile vacuole of Paramecium multimicronucleatum: modification by bisection, fusion and suction J. Exp. Biol., January 1, 2000; 203(2): 239 - 251. [Abstract] [PDF]
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T Tominaga, Y Naitoh, and R. Allen A key function of non-planar membranes and their associated microtubular ribbons in contractile vacuole membrane dynamics is revealed by electrophysiologically controlled fixation of Paramecium J. Cell Sci., January 11, 1999; 112(21): 3733 - 3745. [Abstract] [PDF]
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