Maintenance Of Cell Size Research Articles

Isovolumetric regulation of C6 rat glioma cells in hyperosmotic media.

Volume regulation of C6 glioma cells was studied in response to a gradual increase of extracellular osmolality from 300 to 440 mosmol/kgH2O at 37 degrees C. Maintenance of cell size depended on the rate of osmolality increase (CR): at CR of 3 mosmol.kg-1.min-1, cell volume was kept constant, whereas it decreased progressively at CR of 6 or 9 mosmol.kg-1.min-1. The ability of C6 cells to maintain their volume is termed isovolumetric regulation (IVR). Reducing temperature to 22 degrees C inhibited IVR significantly. Also, bumetanide and ouabain blocked the regulation, while 5-(N,N-dimethyl)amiloride (DMA) did not affect IVR: Extracellular acidification rate (EAR) was studied by microphysiometry. EAR gradually decreased in the presence and increased in the absence of IVR. Experiments with DMA show that these changes in EAR were related to the activity of the Na+/H+ exchanger. It was stimulated by cell shrinkage but not by hyperosmolality itself. Our data demonstrate that C6 glioma cells are able to prevent volume decrease at a low rate of elevation of external osmolality and at 37 degrees C. This process requires electrolyte uptake by the Na(+)-K(+)-2Cl cotransporter and Na+/K+ pump.

Both isoforms of protein phosphatase Z are essential for the maintenance of cell size and integrity in Saccharomyces cerevisiae in response to osmotic stress.

The sequences of two genes encoding the protein-serine/threonine-phosphatases PPZ1 and PPZ2 from Saccharomyces cerevisiae have been determined. The molecular masses of PPZ1 and PPZ2 are 77.5 and 78.5 kDa, respectively, and each protein consists of two distinct domains. The C-terminal half of each molecule is 93% identical in PPZ1 and PPZ2, and comprises the protein-phosphatase catalytic domain, while the N-terminal halves, which are rich in serine and asparagine (PPZ1) or serine and arginine (PPZ2), are only 43% identical. Both N-termini start with the amino acids Met-Gly-Asn, suggesting that after removal of the initiating methionine, the N-terminal glycine of the mature protein is myristoylated. Disruption of the gene encoding either PPZ1 or PPZ2 leads to an increase in cell size and cell lysis, the latter being more pronounced in cells disrupted in PPZ1. Haploid cells carrying a double disruption of PPZ1 and PPZ2 genes also show a marked increase in cell size and cell lysis, which can be significantly reduced by the addition of 1 M sorbitol to the growth medium. These results suggest that PPZ1 and PPZ2 play a role in regulating osmotic stability.

Changes in Carbohydrates and Osmotic Potential during Rhythmic Expansion of Rose Petals

Abstract Rhythmic pulses of irreversible petal expansion in rose (Rosa hybrida L. ‘Sonia’) petals cause diurnal changes in the rate of flower opening. Time-lapse cinematography revealed a transient increase in the rate of rose flower opening that commenced shortly before the onset of a light period and lasted for a few hours. Petal expansion, which occurred sequentially from the outer to the innermost whorl, involved rhythmic increases in fresh and dry weights. The amount of expansion was greatest in the distal portion of each petal and least near the petal base. Periods of rapid expansion were accompanied by decreases in starch and increases in soluble sugars in the petals, but the total carbohydrate content of the petals remained constant during a light–dark cycle. During expansion, the osmotic potential of the outer petal increased from −790 to −690 kPa. Starch hydrolysis during petal growth appears to be important for maintenance of cell size, but it is not the factor controlling cell expansion.

Differential effects of trypsin on the epidermis of Rana catesbeiana

The filamentous cytoskeletons of epidermal cells of the bullfrog (Rana catesbeiana) were investigated by electron microscopy. Following treatment with trypsin, sheets of epithelium were removed from swatches of abdominal skin. Trypsinization produces differential effects on the ultrastructure of the various cell layers. The desmosomes of all layers, except those of the stratum corneum, are split by trypsinization and the resulting desmosomal plaques fastened to tonofilaments are retracted into cells to form deep "inpouchings" of the plasma membranes, while tonofilament bundles become diffuse. Epidermal sheets were gently homogenized to form a suspension of cell remnants with damaged plasma membranes as indicated by vital dye exclusion tests and electron microscopy. Cytoskeletons retain their shapes, yet the lateral distances between individual tonofilaments within bundles appear to increase, thus forming diffuse lacelike structures. These observations support the suggestion that tonofilament bundles, when fastened to desmosomes, have elastic properties. The possible role of the cytoskeletons in the maintenance of cell size and shape in an ion-transporting epithelium is discussed.