Effect of adaptation level on maintained firing and sensitivity in receptive field center of X and Y cells

Summary Maintained firing rates of X cells and Y cells were compared at 6 adaptation levels (AL) between –2.71 log cd/m² and 2.28 log cd/m² (10 mm² pupil size). X cell maintained firing was higher at all ALs and was statistically different at medium and high ones. Changes in AL had nearly identical effects upon X and Y cell suprathreshold sensitivity to a flashing spot in the center of their receptive fields; the Weber function had a slope of 0.744 for Y cells and 0.743 for X cells. These values are not statistically different.This research is supported by Public Health Service grant no. EY 00701.     

Stimulus-response function at several levels of background luminance, in the cat visual areas 17 and 18.

Stimulus-response curves of simple cells of the visual cortex were obtained by using 500-msec stationary stimuli. Background influence on single unit responses was studied. The contrast sensitivity of simple cells increases as a function of background luminance. The resolution power of these cortical cells for detecting differences in stimulus contrast decreases at background levels above 0.09 cd/m2.     

A 41, XYY mouse

Summary Cytogenetic analyses of bone marrow and meiotic cells in an apparently normal male mouse clearly revealed the presence of an extra Y chromosome leading to 2n=41, XYY. During meiosis the sex chromosomes formed all possible types of combinations (XYY, XY/Y, YY/X and X/Y/Y). Compared to 40, XY normal mice, the sperm count was significantly less, but the incidence of sperm head abnormality was at the normal level.Acknowledgment. The authors are grateful to Prof. G. K. Manna, Department of Zoology, Kalyani University, for his valuable comments and Prof. M. C. Dash, School of Life Sciences, Sambalpur University for providing necessary facilities. Thankful acknowledgment to CSIR, India for a SRF awarded to RNK.     

ATP-induced Ca<Superscript>2+</Superscript>-signalling mechanisms in the regulation of mesenchymal stem cell migration

The ability of cells to migrate to the destined tissues or lesions is crucial for physiological processes from tissue morphogenesis, homeostasis and immune responses, and also for stem cell-based regenerative medicines. Cytosolic Ca²⁺ is a primary second messenger in the control and regulation of a wide range of cell functions including cell migration. Extracellular ATP, together with the cognate receptors on the cell surface, ligand-gated ion channel P2X receptors and a subset of G-protein-coupled P2Y receptors, represents common autocrine and/or paracrine Ca²⁺ signalling mechanisms. The P2X receptor ion channels mediate extracellular Ca²⁺ influx, whereas stimulation of the P2Y receptors triggers intracellular Ca²⁺ release from the endoplasmic reticulum (ER), and activation of both type of receptors thus can elevate the cytosolic Ca²⁺ concentration ([Ca²⁺]_c), albeit with different kinetics and capacity. Reduction in the ER Ca²⁺ level following the P2Y receptor activation can further induce store-operated Ca²⁺ entry as a distinct Ca²⁺ influx pathway that contributes in ATP-induced increase in the [Ca²⁺]_c. Mesenchymal stem cells (MSC) are a group of multipotent stem cells that grow from adult tissues and hold promising applications in tissue engineering and cell-based therapies treating a great and diverse number of diseases. There is increasing evidence to show constitutive or evoked ATP release from stem cells themselves or mature cells in the close vicinity. In this review, we discuss the mechanisms for ATP release and clearance, the receptors and ion channels participating in ATP-induced Ca²⁺ signalling and the roles of such signalling mechanisms in mediating ATP-induced regulation of MSC migration.     

Cytotoxicity of mouse peritoneal cells after alloimmunization]

CBA Mice were immunized by two intraperitoneal injections of 30 X 10(6) DBA/2 or C57BL/6 spleen cells at days--12 and--2. Peritoneal cell population was obtained at day zero by washing the peritoneal cavity of Mice. Adherent cells were then separated using a 2 hrs. incubation in "Falcon" plates followed by washing. This macrophage-rich peritoneal cell population was found nonspecifically cytotoxic against 51Cr labeled tumoral target cells: P815 X DBA/2 mastocytoma cells, EL4 X C57BL/L lymphoma cells and spontaneous lymphoma AKR cells (same H--2k as CBA). This adherent peritoneal cell cytoxicity was demonstrated after 24 hrs. incubation with the target cells. It was found in nonspecific combination as well as when using target cells syngeneic to the donor. These findings suggest that adherent peritoneal cell cytotoxicity could be at least partly due to macrophages and result from factor (s) released by sensitized lymphocytes in vivo in the same way as has been previously demonstrated in vitro.     

Evidence of a direct action of triiodothyronine (T3) on the cell membrane of GH3 cells: an electrophysiological approach

Electrophysiological experiments demonstrate that triiodothyronine (T3) exerts a direct effect on the membrane of a strain of cultured rat pituitary tumor cells, GH3/B6. These cells respond to pressure application of T3 (2-5 nl, concentration 1 X 10(-10) M) with an increase in the membrane resistance (Rm) and a hyperpolarization. Spontaneously firing cells become silent.     

Stimulus-response function at several levels of background luminance,in the cat visual areas 17 and 18

Summary Stimulus-response curves of simple cells of the visual cortex were obtained by using 500-msec stationary stimuli. Background influence on single unit responses was studied. The contrast sensitivity of simple cells increases as a function of background luminance. The resolution power of these cortical cells for detecting differences in stimulus contrast decreases at background levels above 0.09 cd/m².This investigation was supported by a grant from the Consiglio Nazionale delle Ricerche, Rome (Italy).     

Photoreactivation of UV damage in cultured Drosophila cells

Cell survival and photoreactivation of 254 nm ultraviolet (UV) light damage in a wild type Drosophila cell line was assayed by colony formation in liquid medium. Fo, Fq, and extrapolation number for the exponential portion of survival curves are 21 J/m2, 3.6 J/m2, and 1.5 for non-photoreactivated cells and 110 J/m2, 11.2 J/m2, and 1.3 for those exposed to photoreactivating light. Maximal photoreactivation occurs at the 100 J/m2 region of the curve. At 10 and 50% survival, 75-80% of the UV damage was photoreactivable.     

Spatial distribution of signal and adaptive sensitivity in the receptive field surrounds of cat retinal ganglion cells

Summary A comparison was made between adaptive and signal sensitivity profiles of the surround response mechanism of cat retinal ganglion cells. The 2 profiles were found to be similar for X cells but the surrounds of Y cells appear to pool adaptation over a smaller retinal region than they pool signals. Acknowledgments. We wish to thank Mr O. Navarro for his valuable technical assistance. This research is supported by Public Health Service grant No. EY 00701.     

Hypergravity promotes cell proliferation

When HeLa cells, chicken embryo fibroblasts, sarcoma Galliera cells, Friend leukemia virus transformed cells and human lymphocytes are cultured in a hypergravitational field (e.g. 10 X g) proliferation rate is increased by 20-30%, whereas glucose consumption per cell is lower than at 1 X g. Tracking of cell movements on gold-coated substrates reveals that cell migration is hindered at high-g. These findings suggest that under gravitational stress the cell is either capable of shifting to other metabolic pathways and/or consumes less energy at high-g than at 1 X g. This work describes ground-based investigations related to experiments to be performed on future Spacelab missions.     

Recruitment of Pyk2 to SHPS-1 signaling complex is required for IGF-I-dependent mitogenic signaling in vascular smooth muscle cells

In vascular smooth muscle cells, IGF-I stimulates SHPS-1/SHP2/Src complex formation which is required for IGF-I-stimulated cell proliferation. Using SHP2/Src silencing and a Pyk2/Y402F mutant, we showed that Pyk2 was also recruited to the SHPS-1 complex. Pyk2 recruitment to SHPS-1 is mediated via the interaction of Pyk2 Tyr402 and the Src in response to IGF-I. Following Src/Pyk2 association, Src phosphorylates Pyk2 on Tyr881 providing a binding site for Grb2. Cells expressing Pyk2/Y881F showed decreased Grb2 recruitment to SHPS-1 and impaired Shc/Grb2 association. This change led to reduced Erk1/2 (MAP kinase) activation and cell proliferation in response to IGF-I. Our results show that, following its recruitment to the SHPS-1 signaling complex, Pyk2 localizes Grb2 in close proximity to Shc thereby facilitating Shc/Grb2 association which leads to Erk1/2 activation in response to IGF-I. Thus, Pyk2 recruitment to SHPS-1 plays an important role in regulating the IGF-I-stimulated mitogenic response.     

Selection of the relevant information set for predictive relationships analysis between time series

In time series analysis, a vector Y is often called causal for another vector X if the former helps to improve the k‐step‐ahead forecast of the latter. If this holds for k=1, vector Y is commonly called Granger‐causal for X . It has been shown in several studies that the finding of causality between two (vectors of) variables is not robust to changes of the information set. In this paper, using the concept of Hilbert spaces, we derive a condition under which the predictive relationships between two vectors are invariant to the selection of a bivariate or trivariate framework. In more detail, we provide a condition under which the finding of causality (improved predictability at forecast horizon 1) respectively non‐causality of Y for X is unaffected if the information set is either enlarged or reduced by the information in a third vector Z . This result has a practical usefulness since it provides a guidance to validate the choice of the bivariate system { X , Y } in place of { X , Y , Z }. In fact, to test the ‘goodness’ of { X , Y } we should test whether Z Granger cause X not requiring the joint analysis of all variables in { X , Y , Z }. Copyright © 2002 John Wiley & Sons, Ltd.     

Tyrosine 842 in the activation loop is required for full transformation by the oncogenic mutant FLT3-ITD

The type III receptor tyrosine kinase FLT3 is frequently mutated in acute myeloid leukemia. Oncogenic FLT3 mutants display constitutive activity leading to aberrant cell proliferation and survival. Phosphorylation on several critical tyrosine residues is known to be essential for FLT3 signaling. Among these tyrosine residues, Y842 is located in the so-called activation loop. The position of this tyrosine residue is well conserved in all receptor tyrosine kinases. It has been reported that phosphorylation of the activation loop tyrosine is critical for catalytic activity for some but not all receptor tyrosine kinases. The role of Y842 residue in FLT3 signaling has not yet been studied. In this report, we show that Y842 is not important for FLT3 activation or ubiquitination but plays a critical role in regulating signaling downstream of the receptor as well as controlling receptor stability. We found that mutation of Y842 in the FLT3-ITD oncogenic mutant background reduced cell viability and increased apoptosis. Furthermore, the introduction of the Y842 mutation in the FLT3-ITD background led to a dramatic reduction in in vitro colony forming capacity. Additionally, mice injected with cells expressing FLT3-ITD/Y842F displayed a significant delay in tumor formation, compared to FLT3-ITD expressing cells. Microarray analysis comparing gene expression regulated by FLT3-ITD versus FLT3-ITD/Y842F demonstrated that mutation of Y842 causes suppression of anti-apoptotic genes. Furthermore, we showed that cells expressing FLT3-ITD/Y842F display impaired activity of the RAS/ERK pathway due to reduced interaction between FLT3 and SHP2 leading to reduced SHP2 activation. Thus, we suggest that Y842 is critical for FLT3-mediated RAS/ERK signaling and cellular transformation.     

Parameters affecting the maximum cell concentration of Tetrahymena

In cultures with efficient aeration a maximum cell concentration (MCC) of 6 X 10(5) cells/ml (defined medium) and 5.5 X 10(6) cells/ml (broth) can be reached. By culturing within Millicells with excess supply of medium and efficient removal of waste products a physical limit for MCC of about 13 X 10(6) cells/ml is reached.     

Surface exposure of phosphatidylserine in pathological cells

The asymmetric phospholipid distribution in plasma membranes is normally maintained by energy-dependent lipid transporters that translocate different phospholipids from one monolayer to the other against their respective concentration gradients. When cells are activated, or enter apoptosis, lipid asymmetry can be perturbed by other lipid transporters (scramblases) that shuttle phospholipids non-specifically between the two monolayers. This exposes phosphatidylserine (PS) at the cells outer surface. Since PS promotes blood coagulation, defective scramblase activity upon platelet stimulation causes a bleeding disorder (Scott syndrome). PS exposure also plays a pivotal role in the recognition and removal of apoptotic cells via a PS-recognizing receptor on phagocytic cells. Furthermore, expression of PS at the cell surface can occur in a wide variety of disorders. This review aims at highlighting how PS expression in different cells may complicate a variety of pathological conditions, including those that promote thromboembolic complications or produce aberrations in apoptotic cell removal.Received 26 November 2004; received after revision 3 January 2005; accepted 10 January 2005 Available online 09 March 2005     

Periodate oxidation of lymphocyte membrane glycoconjugates]

Mouse spleen cells free of erythrocytes were suspended in PBS at a concentration of 2 X 10(7) cells/ml and mixed with an equal volume of sodium periodate in PBS for 10 min. at 4 degrees C to give a final concentration of periodate ranging from 10(-4) M to 5 X 10(-3) M. The cells were then washed and suspended (60 X 10(6) ml) in PBS containing 3H-labelled sodium borohydrate and incubated for 30 min, at 23 degrees C. Following this, the cells were washed and the pellets treated with H2SO4 0.1 N for 60 min. at 80 degrees C. Compounds liberated by such treatment, were identified by chromatography as derivates of sialic acid. The data provide direct evidence that the mitogenic effect of sodium periodate is associated to the oxidation of the sialic acid residues on the lymphocyte membrane.     

Cytosolic phospholipase A2 and lipoxygenase are involved in cell cycle progression in neuroblastoma cells

Arachidonic acid has been implicated in regulating cellular proliferation, and is preferentially released by the 85-kDa cytosolic phospholipase A2 (cPLA2). Recently, we demonstrated that cPLA2 is activated at distinct periods during the ongoing cell cycle of neuroblastoma cells. The purpose of the present study was to establish the role of these cPLA2 activity peaks in cell cycle progression. Inhibition of cPLA2 activity with arachidonyl trifluoromethylketone (ATK) in early G1 phase reduced DNA synthesis markedly. A 24-h incubation with ATK revealed no significant difference in cell number compared to untreated cells, although cPLA2 activity was still inhibited. This suggests redundancy of different PLA2 enzymes. Lipoxygenase inhibition in early G1 resulted in G1 phase arrest, whereas inhibitors for cyclooxygenase had no effect. Furthermore, cells stopped progressing through S phase when lipoxygenase was inhibited in early S phase, demonstrating the requirement of lipoxygenase products for S phase progression.     

人结肠癌CW-2干细胞获取方法研究

目的运用3种不同的方法分离纯化人结肠癌CW-2干细胞,并对其分离纯化效率进行比较,探讨获得癌干细胞的有效方法。方法采用单纯无血清悬浮培养、无血清悬浮培养联合化疗药物、流式细胞分选技术分别富集人结肠癌细胞株CW-2干细胞;然后运用流式细胞术、NOD—SCID小鼠致瘤实验和Transwell侵袭实验分析比较3种方法的富集效率。结果无血清悬浮培养细胞．无血清悬浮培养联合化疗药物处理细胞和流式细胞仪分选技术分选后细胞中具有结肠癌干细胞特性的CD44＋EPCAM_细胞分别为（59．39±4．55）％、（74.36±6．78）％、（86．43±8．43）％;3群细胞的成瘤能力和侵袭能力都存在显著统计学差异（P值〈0．05）：流式细胞分选技术分选后细胞〉无血清悬浮培养联合化疗药物处理细胞〉单纯无血清悬浮培养细胞。结论流式细胞分选技术富集癌干细胞的能力强于单纯无血清悬浮培养和无血清悬浮培养联合化疗药物,无血清悬浮培养联合化疗药物又强于单纯无血清悬浮培养。