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Indoor contaminants were investigated from July 2013 to January 2015 within ninety-five residential houses in five evacuation zones, Iitate village, Odaka district, and the towns of Futaba, Okuma, and Tomioka. A dry smear test was applied to the surface of materials and structures in rooms and in the roof-space of houses. We found that (134)Cs and (137)Cs were the dominant radionuclides in indoor surface contamination, and there was a distance dependence from the Fukushima Daiichi nuclear power plant (FDNPP). For surface contamination in Iitate village (29-49 km from the FDNPP), 24.8% of samples exceeded the detection limit, which is quite a low value, while in Okuma (<3.0 km from the FDNPP), 99.7% of samples exceeded the detection limit and surface contamination levels exceeded 20 Bq/cm(2) (the value was corrected to March 2011). In residential houses in Okuma, Futaba, and Tomioka, closer to the FDNPP than those in Odaka district and Iitate village, surface contamination was inversely proportional to the square of the distance between a house and the FDNPP. In the houses closest to the FDNPP, the contribution of surface contamination to the ambient dose equivalent rate was evaluated to be approximately 0.3 µSv/h.

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The contractile vacuole complex of Paramecium multimicronucleatum transforms into membrane-bound vesicles on excision from the cell. The I-V relationship was linear in a voltage range of -80 to +80 mV in all vesicles, despite being derived from different parts of the contractile vacuole complex. No voltage-gated unit currents were observed in membrane patches from the vesicles. Vesicles derived from the radial arm showed a membrane potential of >10 mV, positive with reference to the cytosol, while those derived from the contractile vacuole showed a residual (<5 mV) membrane potential. The electrogenic V-ATPases in the decorated spongiome are responsible for the positive potential, and Cl- leakage channels are responsible for the residual potential. The specific resistance of the vesicle membrane (approximately 6 kOmega cm2) increased, while the membrane potential shifted in a negative direction when the vesicle rounded. An increase in the membrane tension (to approximately 5 x 10(-3) N m(-1)) is assumed to reduce the Cl- leakage conductance. It is concluded that neither voltage- nor mechano-sensitive ion channels are involved in the control of the fluid segregation and membrane dynamics that govern fluid discharge cycles in the contractile vacuole complex. The membrane vesicles shrank when the external osmolarity was increased, and swelled when the osmolarity was decreased, implying that the contractile vacuole complex membrane is water permeable. The water permeability of the membrane was 4-20 x 10(-7) microm s(-1) Pa(-1). The vesicles containing radial arm membrane swelled after initially shrinking when exposed to higher external osmolarity, implying that the V-ATPases energize osmolyte transport mechanisms that remain functional in the vesicle membrane. The vesicles showed an abrupt (<30 ms), slight, slackening after rounding to the maximum extent. Similar slackening was also observed in the contractile vacuoles in situ before the opening of the contractile vacuole pore. A slight membrane slackening seems to be an indispensable requirement for the contractile vacuole membrane to fuse with the plasma membrane at the pore. The contractile vacuole complex-derived membrane vesicle is a useful tool for understanding not only the biological significance of the contractile vacuole complex but also the molecular mechanisms of V-ATPase activity.

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A fresh water protozoan Paramecium multimicronucleatum adapted to a given solution was found to swell until the osmotic pressure difference between the cytosol and the solution balanced the cytosolic pressure. The cytosolic pressure was generated as the cell swelled osmotically. When either one or both of these pressures was somehow modified, cell volume would change until a new balance between these pressures was established. A hypothetical osmolyte transport mechanism(s) was presumably activated when the cytosolic pressure exceeded the threshold value of approximately 1.5 x 10(5) Pa as the cell swelled after its subjection to a decreased osmolarity. The cytosolic osmolarity thereby decreased and the volume of the swollen cell resumed its initial value. This corresponds to regulatory volume decrease (RVD). By contrast, another hypothetical osmolyte transport mechanism(s) was activated when the cell shrank after its subjection to an increased osmolarity. The cytosolic osmolarity thereby increased and volume of the shrunken cell resumed its initial value. This corresponds to regulatory volume increase (RVI). The osmolyte transport mechanism responsible for RVD might be activated again when the external osmolarity decreases further, and the cytosolic osmolarity thereby decreases to the next lower level. Similarly, another osmolyte transport mechanism responsible for RVI might be activated again when the external osmolarity increases further, and the cytosolic osmolarity thereby increases to the next higher level. Stepwise changes in the cytosolic osmolarity caused by a gradual change in the adaptation osmolarity found in P. multimicronucleatum is attributable to these osmolyte transport mechanisms. An abrupt change in the amount of fluid discharged from the contractile vacuole seen immediately after changing the external osmolarity reduces an abrupt change in cell volume and thereby protects the cell from the disruption of the plasma membrane by excessive stretch or dehydration during shrinkage.

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The freshwater ciliated protozoan, Paramecium multimicronucleatum, usually possesses two contractile vacuole complexes (CVCs). The number of CVCs in a single cell, however, may vary from 1 to 7. We found that the number of cells that have more than two CVCs increased after the cells were exposed to a hypo-osmotic or a high Ca2+ condition. It is assumed that the biological significance of this increase in the number of CVCs is to enhance the cell's ability to eliminate excess water or Ca2+ from the cytosol. An extra CVC was either generated de novo in the posterior region of the cell or, when in the anterior region, by binary fission of the anterior CVC. Generation of these extra CVCs was not inhibited by aphidicolin, a potent inhibitor of DNA synthesis in the micronuclei of Paramecium, even though normal duplication of the CVC that accompanies normal cell division was completely inhibited by this inhibitor. These results suggest that generation of extra CVCs is controlled by a hypothetical regulatory mechanism that is activated either by a hypo-osmotic or by a Ca2+-rich condition and that differs from the regulatory mechanism that governs normal CVC duplication during cell division.

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The contractile vacuole complex is a membrane-bound osmoregulatory organelle of fresh water protozoa such as Paramecium. In Paramecium it consists of a central vacuole (the contractile vacuole) and 5-10 arms that radially extend from the vacuole into the cytosol (the radial arms). Excess cytosolic water, acquired osmotically, is segregated by the radial arms and enters the vacuole, so that the vacuole swells (the fluid-filling phase). The vacuole then rounds (the rounding phase) and the radial arms sever from the vacuole. The vacuole membrane then fuses with the plasma membrane at the pore region and the pore opens. The vacuole shrinks as its fluid is discharged through the pore (the fluid-discharging phase). The pore closes when the fluid has been discharged. The radial arms then reattach to the vacuole, so that the vacuole swells again as the fluid enters from the arms (the next fluid-filling phase). We found that the vacuole continued to show rounding and slackening even after it together with a small amount of cytosol had been isolated from the cell. Using a microcantilever placed on the surface of the vacuole the tension of the in vitro vacuole increased to 5 x 10(-3)N m(-1) as the vacuole rounds, and its lowest value was 1 x 10(-4)N m(-1) during slackening. We propose a hypothesis that an increase in the spontaneous curvature of the organelle's membrane leads to an increase in membrane tension and thus to the vacuole's rounding, severing of the radial arms from the vacuole, and opening of the pore. Conversely, a decrease in the spontaneous curvature accompanied by a decrease in membrane tension could lead to the closing of the pore and reattachment of the radial arm at the start of the fluid-filling phase.

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The electric potential of the contractile vacuole (CV) of Paramecium multimicronucleatum was measured in situ using microelectrodes, one placed in the CV and the other (reference electrode) in the cytosol of a living cell. The CV potential in a mechanically compressed cell increased in a stepwise manner to a maximal value (approximately 80 mV) early in the fluid-filling phase. This stepwise change was caused by the consecutive reattachment to the CV of the radial arms, where the electrogenic sites are located. The current generated by a single arm was approximately 1.3x10(-10) A. When cells adapted to a hypotonic solution were exposed to a hypertonic solution, the rate of fluid segregation, R(CVC), in the contractile vacuole complex (CVC) diminished at the same time as immunological labelling for V-ATPase disappeared from the radial arms. When the cells were re-exposed to the previous hypotonic solution, the CV potential, which had presumably dropped to near zero after the cell's exposure to the hypertonic solution, gradually returned to its maximum level. This increase in the CV potential occurred in parallel with the recovery of immunological labelling for V-ATPase in the radial arm and the resumption of R(CVC) or fluid segregation. Concanamycin B, a potent V-ATPase inhibitor, brought about significant decreases in both the CV potential and R(CVC). We confirm that (i) the electrogenic site of the radial arm is situated in the decorated spongiome, and (ii) the V-ATPase in the decorated spongiome is electrogenic and is necessary for fluid segregation in the CVC. The CV potential remained at a constant high level (approximately 80 mV), whereas R(CVC) varied between cells depending on the osmolarity of the adaptation solution. Moreover, the CV potential did not change even though R(CVC) increased when cells adapted to one osmolarity were exposed to a lower osmolarity, implying that R(CVC) is not directly correlated with the number of functional V-ATPase complexes present in the CVC.

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In vivo K(+), Na(+), Ca(2+) and Cl(-) activities in the cytosol and the contractile vacuole fluid of Paramecium multimicronucleatum were determined in cells adapted to a number of external osmolarities and ionic conditions by using ion-selective microelectrodes. It was found that: (1) under standardized saline conditions K(+) and Cl(-) were the major osmolytes in both the cytosol and the contractile vacuole fluid; and (2) the osmolarity of the contractile vacuole fluid, determined from K(+) and Cl(-) activities only, was always more than 1.5 times higher than that of the cytosol. These findings indicate that excess cytosolic water crosses the contractile vacuole complex membrane osmotically. Substitution of choline or Ca(2+) for K(+) in the external solution or the external application of furosemide caused concomitant decreases in the cytosolic K(+) and Cl(-) activities that were accompanied by a decrease in the water segregation activity of the contractile vacuole complex. This implies that the cytosolic K(+) and Cl(-) are actively coimported across the plasma membrane. Thus, the osmotic gradients across both the plasma membrane and the membrane of the contractile vacuole complex ensure a controlled cascade of water flow through the cell that can provide for osmoregulation as well as the possible extrusion of metabolic waste by the contractile vacuole complex.

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Protozoa living in fresh water are subjected to a hypotonic environment. Water flows across their plasma membrane since their cytosol is always hypertonic to the environment. Many wall-less protozoa have an organelle, the contractile vacuole complex (CVC), that collects and expels excess water. Recent progress shows that most, if not all, CVCs are composed of a two-compartment system encircled by two differentiated membranes. One membrane, which is often divided into numerous vesicles and tubules, contains many proton-translocating V-ATPase enzymes that provide an electrochemical gradient of protons and which fuses only with the membrane of the second compartment. The membrane of the second compartment lacks V-ATPase holoenzymes, expands into a reservoir for fluid storage, and is capable of fusing with the plasma membrane. It is this second compartment that periodically undergoes rounding ("contraction"), setting the stage for fluid expulsion. Rounding is accompanied by increased membrane tension. We review the current state of knowledge on osmolarity, ion concentrations, membrane permeability, and electrophysiological parameters of cells and their contractile vacuoles, where these criteria are helpful to our understanding of the function of the CVC. Effects of environmental stresses on the CVC function are also summarized. Finally, other functions suggested for CVCs based on molecular and physiological studies are reviewed.

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1. The overall membrane potential response of the ciliate Paramecium caudatum to a rise in the temperature of its environment was depolarizing when the ambient temperature before stimulation (Te) was equal to or higher than the culture temperature (Tc), but hyperpolarizing when Te was lower than Tc. 2. The anterior region of the cell responded to a rise in temperature with a localized membrane depolarization. The posterior region was depolarized when Te was equal to or higher than Tc but hyperpolarized when Te was lower than Tc. The Te-dependent polarity reversal of the posterior response was responsible for the comparable reversal of the overall response. 3. The temperature at which the polarity reversal of the posterior response took place shifted according to Tc. This shift caused a comparable shift in the temperature at which polarity reversal occurred for the overall response. 4. The Te-dependent polarity reversal of the posterior response and its Tc-dependence are major causes of thermoaccumulation mediated by ciliary activity of Paramecium in regions with temperatures close to Tc.

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Spermatozoa of the sea urchin, Hemicentrotus pulcherrimus, showed marked decrease in respiration, and arrested movement after interaction with the fixed eggs. Immotile spermatozoa that had reacted with fixed eggs contained higher levels of long chain fatty acyl-CoAs than normal motile spermatozoa. On treatment with carnitine, the immotile spermatozoa became motile again and their intracellular concentrations of long chain fatty acyl-CoAs decreased. On incubation with anti-mycin A or CN- for 20 min, the motility of normal spermatozoa decreased gradually but their long chain fatty acyl-CoA content changed only slightly. The decrease in sperm motility in the latter case was probably due to decrease in the level of ATP, resulting from inhibition of respiration by antimycin A or CN- . The motility of spermatozoa extracted with Triton X-100 was restored by ATP and their movement was inhibited by long chain fatty acyl-CoAs, such as myristoly CoA and palmitoyl-CoA, but was not by short chain fatty acyl-CoAs, such as acetyl-CoA, propionyl CoA and butyryl-CoA. Na-palmitate, Na-myristate and CoA did not inhibit the reactivation of extracted spermatozoa by ATP.