How external osmolarity affects the activity of the contractile vacuole complex, the cytosolic osmolarity and the water permeability of the plasma membrane in Paramecium multimicronucleatum

The rate of fluid expulsion, R(CVC), from the contractile vacuole complex (CVC) of Paramecium multimicronucleatum was estimated from the volume of the contractile vacuoles (CVs) immediately before the start of fluid discharge and from the time elapsing between discharges. The R(CVC) increased when the cell was exposed to a strongly hypotonic solution and decreased in a weakly hypotonic solution. When the cell was exposed to an isotonic or a hypertonic solution, R(CVC) fell to zero. The time constant, tau, used to describe the change in R(CVC) in response to a change in external osmolarity shortened after a short-term exposure to a strongly hypotonic solution and lengthened after a short-term exposure to a less hypotonic solution. A remarkable lengthening of tau occurred after a short-term exposure to isotonic or hypertonic solution. Under natural conditions, mechanisms for controlling R(CVC) are effective in maintaining the cytosolic osmolarity hypertonic within a narrow concentration range despite changes in the external osmolarity, which is normally hypotonic to the cytosol. Cells exposed to an isotonic or hypertonic solution resumed CV activity when left in the solution for 12 h. The cytosolic osmolarity was found to increase and to remain hypertonic to the external solution. This will permit cells to continue to acquire water. The increase in the cytosolic osmolarity occurred in a stepwise fashion, rather than linearly, as the external osmolarity increased. That is, the cytosolic osmolarity first remained more-or-less constant at an increased level until the external osmolarity exceeded this level. Thereupon, the cytosolic osmolarity increased to a new higher level in 12 h, so that the cytosol again became hypertonic to the external solution and the cells resumed CV activity. These results imply that the cell needs to maintain water segregation activity even after it has been exposed to an isotonic or hypertonic environment. This supports the idea that the CVC might be involved not only in the elimination of excess cytosolic water but also in the excretion of some metabolic waste substances.

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Relationship between the membrane potential of the contractile vacuole complex and its osmoregulatory activity inParamecium multimicronucleatum

Journal of Experimental Biology ◽

10.1242/jeb.205.20.3261 ◽

2002 ◽

Vol 205 (20) ◽

pp. 3261-3270 ◽

Cited By ~ 4

Author(s):

Heidi K. Grønlien ◽

Christian Stock ◽

Marilynn S. Aihara ◽

Richard D. Allen ◽

Yutaka Naitoh

Keyword(s):

Reference Electrode ◽

Maximum Level ◽

The Other ◽

Contractile Vacuole ◽

Hypertonic Solution ◽

Hypotonic Solution ◽

Atpase Inhibitor ◽

Filling Phase ◽

High Level

SUMMARYThe 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 1.3×10-10 A. When cells adapted to a hypotonic solution were exposed to a hypertonic solution, the rate of fluid segregation, RCVC, 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 RCVC or fluid segregation. Concanamycin B, a potent V-ATPase inhibitor, brought about significant decreases in both the CV potential and RCVC. 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 RCVC varied between cells depending on the osmolarity of the adaptation solution. Moreover, the CV potential did not change even though RCVC increased when cells adapted to one osmolarity were exposed to a lower osmolarity, implying that RCVC is not directly correlated with the number of functional V-ATPase complexes present in the CVC.

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Short-term control of maize cell and root water permeability through plasma membrane aquaporin isoforms

Plant Cell & Environment ◽

10.1111/j.1365-3040.2011.02429.x ◽

2011 ◽

Vol 35 (1) ◽

pp. 185-198 ◽

Cited By ~ 75

Author(s):

CHARLES HACHEZ ◽

DMITRY VESELOV ◽

QING YE ◽

HAGEN REINHARDT ◽

THORSTEN KNIPFER ◽

...

Keyword(s):

Plasma Membrane ◽

Water Permeability ◽

Short Term ◽

Maize Cell

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Ethanol stimulates glucose uptake and translocation of GLUT-4 in H9c2 myotubes via a Ca2+-dependent mechanism

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.2000.279.6.e1358 ◽

2000 ◽

Vol 279 (6) ◽

pp. E1358-E1365 ◽

Cited By ~ 18

Author(s):

Bo Yu ◽

Adrienne Schroeder ◽

Laura E. Nagy

Keyword(s):

Plasma Membrane ◽

Glucose Uptake ◽

Glucose Homeostasis ◽

Term Treatment ◽

Glucose Disposal ◽

Phosphatidylinositol 3 Kinase ◽

Short Term ◽

Short Term Treatment ◽

Glut 4 ◽

Short Term Exposure

Short-term exposure to ethanol impairs glucose homeostasis, but the effects of ethanol on individual components of the glucose disposal pathway are not known. To understand the mechanisms by which ethanol disrupts glucose homeostasis, we have investigated the direct effects of ethanol on glucose uptake and translocation of GLUT-4 in H9c2 myotubes. Short-term treatment with 12.5–50 mM ethanol increased uptake of 2-deoxyglucose by 1.8-fold in differentiated myotubes. Pretreatment of H9c2 myotubes with 100 nM wortmannin, an inhibitor of phosphatidylinositol 3-kinase, had no effect on ethanol-induced increases in 2-deoxyglucose uptake. In contrast, preincubation with 25 μM dantrolene, an inhibitor of Ca2+release from the sarcoplasmic reticulum, blocked the stimulation of 2-deoxyglucose uptake by ethanol. Increased 2-deoxyglucose uptake after ethanol treatment was associated with a decrease in small intracellular GLUT-4 vesicles and an increase in GLUT-4 localized at the cell surface. In contrast, ethanol had no effect on the quantity of GLUT-1 and GLUT-3 at the plasma membrane. These data demonstrate that physiologically relevant concentrations of ethanol disrupt the trafficking of GLUT-4 in H9c2 myotubes resulting in translocation of GLUT-4 to the plasma membrane and increased glucose uptake.

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Unicellular Microcystis aeruginosa cannot revert back to colonial form after short-term exposure to natural conditions

Biochemical Systematics and Ecology ◽

10.1016/j.bse.2013.08.027 ◽

2013 ◽

Vol 51 ◽

pp. 104-108 ◽

Cited By ~ 11

Author(s):

Linlin Geng ◽

Baoli Qin ◽

Zhou Yang

Keyword(s):

Microcystis Aeruginosa ◽

Natural Conditions ◽

Short Term ◽

Colonial Form ◽

Short Term Exposure

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Osmoregulation inParamecium: in situ ion gradients permit water to cascade through the cytosol to the contractile vacuole

Journal of Cell Science ◽

10.1242/jcs.115.11.2339 ◽

2002 ◽

Vol 115 (11) ◽

pp. 2339-2348 ◽

Cited By ~ 7

Author(s):

Christian Stock ◽

Heidi K. Grønlien ◽

Richard D. Allen ◽

Yutaka Naitoh

Keyword(s):

Plasma Membrane ◽

Water Flow ◽

External Solution ◽

Contractile Vacuole ◽

External Application ◽

Ion Gradients ◽

Complex Membrane ◽

Flow Through

In vivo K+, Na+, Ca2+ 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 Ca2+ 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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The Effect of Dimethyl Sulfoxide on In Vitro Platelet Function

Thrombosis and Haemostasis ◽

10.1055/s-0038-1648027 ◽

1976 ◽

Vol 36 (01) ◽

pp. 221-229 ◽

Cited By ~ 16

Author(s):

Charles A. Schiffer ◽

Caroline L. Whitaker ◽

Morton Schmukler ◽

Joseph Aisner ◽

Steven L. Hilbert

Keyword(s):

Platelet Count ◽

Platelet Aggregation ◽

Dimethyl Sulfoxide ◽

Platelet Function ◽

Platelet Volume ◽

Short Term ◽

Platelet Factor ◽

Short Term Exposure ◽

Structural Abnormalities

SummaryAlthough dimethyl sulfoxide (DMSO) has been used extensively as a cryopreservative for platelets there are few studies dealing with the effect of DMSO on platelet function. Using techniques similar to those employed in platelet cryopreservation platelets were incubated with final concentrations of 2-10% DMSO at 25° C. After exposure to 5 and 10% DMSO platelets remained discoid and electron micrographs revealed no structural abnormalities. There was no significant change in platelet count. In terms of injury to platelet membranes, there was no increased availability of platelet factor-3 or leakage of nucleotides, 5 hydroxytryptamine (5HT) or glycosidases with final DMSO concentrations of 2.5, 5 and 10% DMSO. Thrombin stimulated nucleotide and 5HT release was reduced by 10% DMSO. Impairment of thrombin induced glycosidase release was noted at lower DMSO concentrations and was dose related. Similarly, aggregation to ADP was progressively impaired at DMSO concentrations from 1-5% and was dose related. After the platelets exposed to DMSO were washed, however, aggregation and release returned to control values. Platelet aggregation by epinephrine was also inhibited by DMSO and this could not be corrected by washing the platelets. DMSO-plasma solutions are hypertonic but only minimal increases in platelet volume (at 10% DMSO) could be detected. Shrinkage of platelets was seen with hypertonic solutions of sodium chloride or sucrose suggesting that the rapid transmembrane passage of DMSO prevented significant shifts of water. These studies demonstrate that there are minimal irreversible alterations in in vitro platelet function after short-term exposure to DMSO.

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