Measures of viability in isolated cells

Various methods were compared for estimation of cell viability. Cell count, uptake of trypan blue, release of cellular LDH, as well as cell contents of K+ and Na+ were determined in leukocytes, spleen cells, and Ehrlich cells exposed to adverse conditions. After incubation of these cells with NaF, the cell count remained essentially constant; the extent of cell staining and release of LDH increased to a limited level in suspensions of leukocytes and spleen cells and was virtually unchanged in experiments with Ehrlich cells. On the other hand, pretreatment with NaF induced rapid and marked changes in contents of K+ and Na+ in all three cell types. Exposure of the cells to hypertonic conditions caused more pronounced, but similar overall effects. As a consequence of increased tonicity, the cell count decreased and considerable leakage of LDH occurred in all the cells investigated. Whereas the contents of K+ and Na+ in all pretreated cells changed markedly, the cellular uptake of trypan blue was again the least responsive index of cell permeability. The results showed cell staining by trypan blue to be a relatively poor measure of cell viability and suggest use of the ratio cellular K+/Na+ or, even more efficiently, the cell content of K+ as sensitive indicators of plasma membrane integrity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22041/1/0000459.pd

Exposure to fluctuating salinity enhances free amino acid accumulation in Tigriopus californicus (Copepoda)

Intracellular concentrations of free amino acids (FAA) in the intertidal copepod Tigriopus californicus increase in response to hyperosmotic stress and decrease in response to hypo-osmotic stress. The purpose of this study was to determine if exposure to repeated bouts of osmotic stress resulted in changes in FAA accumulation or the degree of FAA retention in subsequent episodes. Five groups of T. californicus were exposed for 22 days to a fluctuating salinity regime which consisted of 24 h at 100% seawater followed by 24 h at either 90, 80, 70, 60 or 50% seawater (11 cycles). After the tenth exposure to 100% seawater, individuals from each treatment group were analyzed for alanine and proline concentration. Alanine and proline accumulation generally increased in proportion to the osmotic stress up to 60–100% seawater — additional osmotic stress failed to increase total accumulation. Prior exposure to fluctuating salinity increased the extent of alanine and proline retention observed upon transfer to a hypo-osmotic medium. The treatment group which had experienced the most extreme fluctuation (50–100% seawater) retained alanine and proline levels approximately 10- and 20-fold higher, respectively, than controls. A less severe salinity fluctuation was required to elicit this response for alanine (90–100% seawater) than for proline (60–100% seawater). Previous exposure to fluctuating salinity also resulted in increased alanine and proline accumulation in subsequent episodes of hyperosmotic stress. 24 h after transfer from 50 to 100% seawater, alanine and proline levels in the conditioned copepods were approximately 3- and 7-fold higher, respectively, than in copepods which had not been cycled. This facilitation in alanine and proline accumulation occurred after 10 and 11 cycles, respectively. Of the increased accumulation in alanine and proline, 7.0% and 22.5%, respectively, could be accounted for by the higher degree of FAA retention while under hypo-osmotic conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47130/1/360_2004_Article_BF00692733.pd

L'origine des espèces et l'évolutionnisme à partir de 1745

Schoffeniels Ernest. L'origine des espèces et l'évolutionnisme à partir de 1745. In: Bulletin de la Classe des sciences, tome 69, 1983. pp. 240-256