Differences in blastema-associated proteins according to position along body axis in regenerating planarians

To test the hypothesis that neoblasts in different positions in regenerating pieces of planarians may be differentially responsive to diffusible stimuli through differentially expressed membrane receptors, we compared membrane surface proteins in blastemas induced at various positions along an anterior-posterior axis in Dugesia gonocephala (Dugès). The proteins were biotinylated and identified by molecular weight in SDS-PAGE (sodium-dodecylsulfate polyacrilamide gel electrophoresis). This SDS-PAGE pattern was then compared with that of N-glycosylated proteins incorporating ³H-mannose. One 20 kDa glycoprotein present in all blastemas at 3 d was absent from more anterior blastemas at 6 d irrespective of whether those blastemas were at the cephalic or the caudal end of the regenerating piece. The expression of this protein appears to be determined by the position of the blastema along the body axis rather than by its prospective fate.     

Intracellular free zinc and zinc buffering in human red blood cells

Summary The effect of vasopressin on voltage-sensitive Ca²⁺ currents in the rat insulinoma cell line RINm5F has been investigated in patch-clamp whole-cell and single-channel current recording experiments. In the whole-cell recording configuration the dominant inward current in the presence of tetrodotoxin was noninactivating and had a high voltage threshold. This current was much enhanced when external Ca²⁺ was replaced by Ba²⁺ and was blocked by 1 m nifedipine. It can therefore be classified as an L-current. Vasopressin enhanced the L-current without changing the voltage threshold of activation or the voltage at which the peak current was observed. Vasopressin effects were seen at concentrations as low as 0.01nm, and the maximal effect was observed at about 1nm. In higher concentrations the vasopressin effects were weaker, with effects at 50nm of about the same magnitude as at 0.01nm. In single-channel current recording experiments carried out with the cell-attached configuration there were no effects on single L-channel currents when vasopressin was added to the bath solution, but in experiments in which vasopressin (5nm) was infused into the patch pipette a marked increase in the apparent channel open state probability was observed. We conclude that vasopressin, a peptide that is known to markedly enhance glucose-evoked insulin secretion, stimulates opening of the voltage-sensitive Ca²⁺ channels in insulin-secreting cells.     

Intracellular ion concentrations and cell volume during cholinergic stimulation of eccrine secretory coil cells

Summary Methacholine (MCh)-induced changes in intracellular concentrations of Na, K, and Cl ([Na]_i, [K]_i, and [Cl]_i, respectively) and in cellular dry mass (a measure of cell shrinkage) were examined in isolated monkey eccrine sweat secretory coils by electron probe X-ray microanalysis using the peripheral standard method. To further confirm the occurrence of cell shrinkage during MCh stimulation, the change in cell volume of dissociated clear and dark cells were directly determined under a light microscope equipped with differential interference contrast (DIC) optics. X-ray microanalysis revealed a biphasic increase in cellular dry mass in clear cells during continuous MCh stimulation; an initial increase of dry mass to 158% (of control) followed by a plateau at 140%, which correspond to the decrease in cell volume of 37 and 29%, respectively. The latter agrees with the MCh-induced cell shrinkage of 29% in dissociated clear cells. The MCh-induced increase in dry mass in myoepithelial cells was less than half that of clear cells. During the steady state of MCh stimulation, both [K]_i and [Cl]_i of clear cells decreased by about 45%, whereas [Na]_i increased in such a way as to maintain the sum of [Na]_i+[K]_i constant. There was a small (12–15mm) increse in [Na]_i and a decrease in [K]_i in myoepithelial cells during stimulation with MCh. Dissociated dark cells failed to significantly shrink during MCh stimulation. The decrease in [Cl]_i in the face of constant [Na]_i+[K]_i suggests the accumulation of unknown anion(s) inside the clear cell during MCh stimulation. While the decrease in [K]_i and [Cl]_i may be instrumental in facilitating influx of ions via Na–K–2Cl cotransporters, the functional significance of MCh-induced cell shrinkage remains unknown.     

Classical Conditioning-Induced Changes in Low-Molecular-Weight GTP-Binding Proteins in Rabbit Hippocampus

Classical conditioning of Hermissenda, involving paired light-rotation events, results in a 30-35% decrease in the levels of a 20-kDa G protein (cp20). To test whether a similar protein exists in vertebrates, rabbits were trained to associate a tone with periorbital electrical stimulation and G proteins were analyzed by photoaffinity labeling with [alpha-32P]GTP-azidoanilide. A 20-kDa G protein similar to cp20 decreased by 36% in the hippocampus of rabbits subjected to paired tone and electrical stimulation, but not in unpaired controls. Learning-specific decreases were also found in the amount of ras protein.     

Influence of temperature and salinity on carbon and nitrogen content in Dunaliella viridis teodoresco under nitrogen sufficiency

Cell carbon and nitrogen in D. viridis are strongly dependent on the culturing conditions. Both elements increase with increasing salinity. At 31°C cell carbon is maximum and cell nitrogen minimum. This temperature was described previously (Jiménez, C., Niell, F. X. & Fernandez, J. A. (1990). Hydrobiologia, 197, 165-72) as the optimal one for achieving the maximum oxygen evolution. These results point out a possible competence for the reducing power during carbon and nitrogen assimilation processes, and under conditions of high photosynthesis (carbon assimilation) there is a partial inhibition of nitrate reduction, making C:N ratio maximum under conditions of maximum net photosynthesis.The study of cell glycerol, nitrate, structural proteins and free amino acids indicates that all of these solutes accumulate in the cells as a result of the high salinity adaptation.     

Cell fragility — The key problem of microalgae mass production in closed photobioreactors

The gap between the theoretical biological potential of microalgae and the biomass productivity obtained with algal culture in tubular biophotoreactors is due to a reduced growth rate related to hydrodynamic stress of pumping. High levels of mixing are necessary to reach a turbulent flow of the culture, in order to optimize the light regime. The optimal conditions of pumping to produce this significant liquid mixing may produce some cell damage. Factors affecting this hydrodynamic stress (geometry of the bioreactor involved, type of pump utilized, morphology of algal cells, physiological conditions of microalgae, etc.) are discussed.     

红金麻——木槿属一个新杂种

<正> 红金麻 新杂种 Hibiscus×hongjinma Y. T. Chang, hybr. nov. H. cannabinus L. ♀× H. radiatus Cav.♂ Hybrida hortensis ( 2n=30+6sat) θ Hibisco cannabino L. ( 2n=32+4sat) et H. ranndiato Cav. (2n=70+2sat) exorta, Habitu illo simil, characteribus ad hoc magis accedit; ab illo differt floribus purpureis, folio prope basin 3—5     

视黄酸和亚硒酸钠对肝癌细胞某些表型逆转的加和作用

 人肝癌细胞株SMMC-7721经1μmol/L视黄酸和或2.5μmol/L亚硒酸钠处理后,膜上纤维连接蛋白沉着量逐日上升,且较相应天数的对照组细胞增加,而甲胎蛋白分泌量和~3H-TdR参入率被明显抑制。视黄酸和亚硒酸钠同时处理的联合组作用强度接近于两者单独使用时作用强度的加和。对以上结果和视黄酸及亚硒酸钠使肝癌细胞接触抑制恢复及表型逆转的关系作了讨论。     

~3H-TdR放射线转化C3H/10T1/2细胞株转化生长因子α的研究

本文通过斑点印渍杂交技术和放射免疫分析方法,首次证实,~3H-TdR放射线转化C3H/10T1/2细胞株可高表达TGFα mRNA,并可向细胞外分泌具有免疫活性的TGFα分子,而非转化对应细胞中虽有TG FαmRNA的弱表达,但其无血清培养上清中未测到TGFα的分泌。表明TGFα参与了放射线对细胞的转化以及维持转化细胞增殖的过程。提示TGFα在三大致癌因素转化细胞中的存在可能具有普遍意义。同时,c-myc与c-fos两种癌基因mRNA在转化细胞中的表达水平显著高于非转化对应细胞,而c-sis癌基因mRNA的表达水平在两种细胞中无显著差异。