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Ouabain-induced cytoplasmic vesicles and their role in cell volume maintenance.

Russo MA, Morgante E, Russo A, van Rossum GD, Tafani M - Biomed Res Int (2015)

Bottom Line: Na(+)/K(+)-pump may be blocked by ouabain, a digitalic derivative, by inhibition of ATP, or by drastic ion alterations of extracellular fluid.In particular, hepatocytes were able to sequester ions and water in intracellular vesicles and then secrete them at the bile canaliculus pole.This review summarizes evidences regarding this mechanism, problems that are still pending, and questions that need to be answered.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular and Cellular Pathology, IRCCS San Raffaele Pisana, Via di Val Cannuta 247, 00166 Roma, Italy.

ABSTRACT
Cellular swelling is controlled by an active mechanism of cell volume regulation driven by a Na(+)/K(+)-dependent ATPase and by aquaporins which translocate water along the osmotic gradient. Na(+)/K(+)-pump may be blocked by ouabain, a digitalic derivative, by inhibition of ATP, or by drastic ion alterations of extracellular fluid. However, it has been observed that some tissues are still able to control their volume despite the presence of ouabain, suggesting the existence of other mechanisms of cell volume control. In 1977, by correlating electron microscopy observation with ion and water composition of liver slices incubated in different metabolic conditions in the presence or absence of ouabain, we observed that hepatocytes were able to control their volume extruding water and recovering ion composition in the presence of ouabain. In particular, hepatocytes were able to sequester ions and water in intracellular vesicles and then secrete them at the bile canaliculus pole. We named this "vesicular mechanism of cell volume control." Afterward, this mechanism has been confirmed by us and other laboratories in several mammalian tissues. This review summarizes evidences regarding this mechanism, problems that are still pending, and questions that need to be answered. Finally, we shortly review the importance of cell volume control in some human pathological conditions.

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Related in: MedlinePlus

Effects of Brefeldin A on water transport and ultrastructure in the presence of 2 mM ouabain. Liver slices were incubated as described before (see also [7]). (a) Water transport inhibition. (b) Detail of Golgi region of two adjacent hepatocytes: evident Golgi disruption, with only small vesicles left. BC = bile canaliculus.
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fig4: Effects of Brefeldin A on water transport and ultrastructure in the presence of 2 mM ouabain. Liver slices were incubated as described before (see also [7]). (a) Water transport inhibition. (b) Detail of Golgi region of two adjacent hepatocytes: evident Golgi disruption, with only small vesicles left. BC = bile canaliculus.

Mentions: In the model proposed, in Figure 9, water that accumulates when Na+/K+-pump is inhibited by ouabain must be delocalized from cytosol and other compartments leading to the formation of vesicles. During a time-course of the recovery at warm incubation, in the presence or absence of ouabain, vesicles appear to originate by expansion of terminal cisternae of the endoplasmic reticulum and of Golgi elements [6] and have acidic contents [32] and their formation is dependent on the presence of Cl− (Figures 3(a) and 3(b)) and vacuolar H+-ATPase [33, 34] and, finally, on the integrity of Golgi apparatus, as demonstrated by treatment with Brefeldin A, which prevents vesicles formation (Figures 4(a) and 4(b)), extrusion of water, and recovery of ions [7]. The entry of chloride into vesicles represents the driving force for transport of Na+ and water. In fact, replacement of Cl− in the medium with NO3− or SO42− efficiently prevented water extrusion in the presence of ouabain (Table 2) and vesicles were almost absent (Figure 3(b)). Transfer of these slices in a medium containing chloride after only 15 min at 38°C leads to water extrusion (Figure 3(a)) and the appearance of vesicles [24, 25, 30]. The diuretic furosemide, which inhibits cotransport of Na+ and Cl−, caused effects similar to the absence of chloride [30].


Ouabain-induced cytoplasmic vesicles and their role in cell volume maintenance.

Russo MA, Morgante E, Russo A, van Rossum GD, Tafani M - Biomed Res Int (2015)

Effects of Brefeldin A on water transport and ultrastructure in the presence of 2 mM ouabain. Liver slices were incubated as described before (see also [7]). (a) Water transport inhibition. (b) Detail of Golgi region of two adjacent hepatocytes: evident Golgi disruption, with only small vesicles left. BC = bile canaliculus.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4383472&req=5

fig4: Effects of Brefeldin A on water transport and ultrastructure in the presence of 2 mM ouabain. Liver slices were incubated as described before (see also [7]). (a) Water transport inhibition. (b) Detail of Golgi region of two adjacent hepatocytes: evident Golgi disruption, with only small vesicles left. BC = bile canaliculus.
Mentions: In the model proposed, in Figure 9, water that accumulates when Na+/K+-pump is inhibited by ouabain must be delocalized from cytosol and other compartments leading to the formation of vesicles. During a time-course of the recovery at warm incubation, in the presence or absence of ouabain, vesicles appear to originate by expansion of terminal cisternae of the endoplasmic reticulum and of Golgi elements [6] and have acidic contents [32] and their formation is dependent on the presence of Cl− (Figures 3(a) and 3(b)) and vacuolar H+-ATPase [33, 34] and, finally, on the integrity of Golgi apparatus, as demonstrated by treatment with Brefeldin A, which prevents vesicles formation (Figures 4(a) and 4(b)), extrusion of water, and recovery of ions [7]. The entry of chloride into vesicles represents the driving force for transport of Na+ and water. In fact, replacement of Cl− in the medium with NO3− or SO42− efficiently prevented water extrusion in the presence of ouabain (Table 2) and vesicles were almost absent (Figure 3(b)). Transfer of these slices in a medium containing chloride after only 15 min at 38°C leads to water extrusion (Figure 3(a)) and the appearance of vesicles [24, 25, 30]. The diuretic furosemide, which inhibits cotransport of Na+ and Cl−, caused effects similar to the absence of chloride [30].

Bottom Line: Na(+)/K(+)-pump may be blocked by ouabain, a digitalic derivative, by inhibition of ATP, or by drastic ion alterations of extracellular fluid.In particular, hepatocytes were able to sequester ions and water in intracellular vesicles and then secrete them at the bile canaliculus pole.This review summarizes evidences regarding this mechanism, problems that are still pending, and questions that need to be answered.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Molecular and Cellular Pathology, IRCCS San Raffaele Pisana, Via di Val Cannuta 247, 00166 Roma, Italy.

ABSTRACT
Cellular swelling is controlled by an active mechanism of cell volume regulation driven by a Na(+)/K(+)-dependent ATPase and by aquaporins which translocate water along the osmotic gradient. Na(+)/K(+)-pump may be blocked by ouabain, a digitalic derivative, by inhibition of ATP, or by drastic ion alterations of extracellular fluid. However, it has been observed that some tissues are still able to control their volume despite the presence of ouabain, suggesting the existence of other mechanisms of cell volume control. In 1977, by correlating electron microscopy observation with ion and water composition of liver slices incubated in different metabolic conditions in the presence or absence of ouabain, we observed that hepatocytes were able to control their volume extruding water and recovering ion composition in the presence of ouabain. In particular, hepatocytes were able to sequester ions and water in intracellular vesicles and then secrete them at the bile canaliculus pole. We named this "vesicular mechanism of cell volume control." Afterward, this mechanism has been confirmed by us and other laboratories in several mammalian tissues. This review summarizes evidences regarding this mechanism, problems that are still pending, and questions that need to be answered. Finally, we shortly review the importance of cell volume control in some human pathological conditions.

Show MeSH
Related in: MedlinePlus