Third Of Cells Research Articles

Photovoltaic integration in curved parts: Mechanical limits and key parameters from a theoretical point of view

AbstractPhotovoltaic cells are produced as thin flat layers. They behave as a brittle and elastic material that fails at a given level of stress. Conforming cells into curved geometries will a priori induce both flexure and membrane stresses. In the present work, an analytical model is derived to predict both stress distributions and intensities in a mono‐crystalline pseudo‐square cell. Furthermore, a second model is derived to find the main stresses within fractions of cells. For conventional cell dimensions, solutions predict a transition from flexure to membrane dominated stresses for most conformations as curvature increases. As a consequence, near failure stresses are mainly determined by cells size and aspect ratio. In contrast, flexion is the main contribution in a small subset of the curvature space or for small curvatures. In the corresponding cases, stresses scale in proportion to cells thickness. As a consequence, cell size and/or shape is the main parameter to reduce internal stresses in most cases. In particular, the use of fractions of cells can substantially decrease membrane stresses and thus increase the maximum curvature. For instance, in a case study with M0 cells and curvature radii of a few meters, the highest predicted tensile stress is 45 . In such a case, the larger M12 format gives a prediction of . In contrast, thirds of cells give predictions of 25 and , respectively.

Cdc42 and Par proteins stabilize dynamic adherens junctions in the Drosophila neuroectoderm through regulation of apical endocytosis

Cell rearrangements require dynamic changes in cell–cell contacts to maintain tissue integrity. We investigated the function of Cdc42 in maintaining adherens junctions (AJs) and apical polarity in the Drosophila melanogaster neuroectodermal epithelium. About one third of cells exit the epithelium through ingression and become neuroblasts. Cdc42-compromised embryos lost AJs in the neuroectoderm during neuroblast ingression. In contrast, when neuroblast formation was suppressed, AJs were maintained despite the loss of Cdc42 function. Loss of Cdc42 function caused an increase in the endocytotic uptake of apical proteins, including apical polarity factors such as Crumbs, which are required for AJ stability. In addition, Cdc42 has a second function in regulating endocytotic trafficking, as it is required for the progression of apical cargo from the early to the late endosome. The Par complex acts as an effector for Cdc42 in controlling the endocytosis of apical proteins. This study reveals functional interactions between apical polarity proteins and endocytosis that are critical for stabilizing dynamic basolateral AJs.

Phenotypic and Morphological Characterization of In Vitro Oligodendrogliogenesis

The neurosphere assay has been used to maintain neural progenitor cells (NPCs) in the undifferentiated state. These cells are multipotent and gave rise to neurons and glial cells. Here we show that within 10 days of culture, neurospheres contained precursors and differentiated progeny of all three major central nervous system (CNS) cell lineages and these occupied distinct zones. The microenvironment of the inner zone supported cell differentiation. Cells of oligodendroglial lineage generated within the neurosphere were frequently observed. Of these cells, A2B5(+) cells were homogeneously distributed in the neurospheres, NG2(+) cells preferentially occupied the outer zone and O4(+) cells were localized at the inner zone of 10 day-old neurospheres. We prevented a massive cell death of dissociated neurosphere cells seen after differentiation triggered with adhesion and fetal calf serum by adding epidermal growth factor and basic fibroblast growth factor to the culture medium. Under these conditions, less than one third of cells did not express cell specific markers, glial fibrillary acidic protein-positive astroglia represented 43.4%, NG2(+) and/or O4(+) oligodendroglia represented 24.3%, and betaIII-tubulin(+) neurons 3.1% of cells recovered after neurosphere differentiation. We present evidence that oligodendroglial cells differentiate in a stepwise process as a result of their distribution in subsets that represent distinct developmental stages according to antigenic and morphological criteria. These include oligodendrocyte progenitors, preoligodendrocytes, and oligodendrocytes. The highly complex morphology of mature oligodendrocytes was compatible with functional cells.

Image features selected by neurons of the cat primary visual cortex.

The sensitivity of neurons in field 17 of the visual cortex in cats to cross-shaped, Y-shaped, and star-shaped figures flashing in the receptive field was studied. About 40% of the neurons studied (114 of 289) were found to generate large responses (with an average response factor of 3.06 +/- 0.32) to one of the figures flashing in the center of the receptive field, as compared with the responses produced to a single bar in the optimal orientation. Most of these neurons (72%) were selectively sensitive to the shape and orientation of figures; the remainder demonstrated some degree of tuning invariance to these properties. The latent periods of responses to figures were usually shorter than those of responses to bars. Tuning parameters for bars and figures were generally related: neurons with acute orientational tuning to a bar were usually highly selective to both the configuration and the orientation people figures. Separate or combined stimulation with crosses in the center and near periphery of the receptive fields demonstrated summation, antagonism, or the lack of any interaction between these zones in producing sensitivity to crosses. Local blockade of intracortical GABAergic inhibition by microiontophoretic application of bicuculline showed that in one third of the neurons studied, sensitivity to figures was generated or enhanced by inhibition in normal conditions, while one third of cells showed suppression by inhibition, and sensitivity in the remainder was independent of inhibition. These data show that reconsideration of existing concepts of the role of field 17 in selecting only first-order shape features of images (i.e., the orientations of single lines) is needed, since almost half the neurons in the cat primary visual cortex can efficiently detect second-order features (angles and line intersections).

Characterisation of mucosal lymphoid aggregates in ulcerative colitis: immune cell phenotype and TcR-γδ expression

BACKGROUND AND AIMSA histopathological feature considered indicative of ulcerative colitis (UC) is the so-called basal lymphoid aggregates. Their relevance in the pathogenesis of UC is, however, unknown. We have performed...

Proliferation and apoptosis of human T cells during replicative senescence--a critical approach.

Normal human T lymphocytes growing in culture undergo replicative senescence. Previously, we have shown that in our conditions polyclonal T cells cease proliferation after about three weeks (Radziszewska et al., 1999, Cell Biol. Int. 23, 97-103). Now we present results of a more detailed analysis of in vitro growth as well as phenotypic changes of T cells. Cell cycle analysis showed that about 20% of cells were in the S phase until the 17th day of culture (young cells). The highest number of mitotic cells (phase G2/M; 10%) was observed during the first week of culture. All not dividing senescent cells were stopped in the G1 phase (after the 30th day of culture). The sub-G1 fraction which represents apoptotic cells did not exceed 8% during the whole period until the 30th day of culture. During in vitro T-cell growth, a rather rapid selection to CD3+ CD8+ cells occurs. In the presenescent (between the 17th and 30th day) and senescent populations the majority of cells (above 90%) were CD8 positive. We also have checked the expression of alpha-chain interleukin-2 (IL-2) receptor (CD25). In young and presenescent cells about one third of cells was CD25 positive, but only 15% in the pool of senescent cells. Immunoblotting analysis of p16 protein recognized previously as a marker of senescent T cells, showed its highest and transient expression in presenescent cells. A critical review of the polyclonal T cell replicative senescence model is presented.

Expression and function of NKRP1A molecule on human monocytes and dendritic cells.

In this study, we analyzed the expression and function of the lymphocyte surface lectin NKRP1A on peripheral blood monocytes (Mo) or Mo and dendritic cells (DC) derived from thymic and bone marrow precursors. De novo expression of NKRP1A and CD14 molecules was detected upon culture of CD2- CD3- CD14- CD16- CD1a- NKRP1A- immature thymic precursors for 7 days in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF). Under these culture conditions, by day 21, a fraction of cells had lost CD14 and acquired both CD80 (B7.1) and CD86 (B7.2) molecules. These cells displayed a DC-like morphology and were surface NKRP1A positive. CD34+ NKRP1A- CD14- precursors, isolated from bone marrow and cultured in the presence of GM-CSF, also expressed both NKRP1A and CD14: these antigens were newly expressed on about one third of cells which had lost the CD34 precursor marker. In addition, NKRP1A was constitutively present on resting CD14+ peripheral blood Mo. When these cells were cultured in the presence of GM-CSF, the resulting DC population retained the expression of NKRP1A and acquired CD80, while they lost the CD14 antigen. Functional analysis revealed that the engagement of NKRP1A molecule leads to a strong intracellular calcium ([Ca2+]i) increase both in resting peripheral blood Mo and in vitro-derived DC. [Ca2+]i increase was mainly due to extracellular calcium influx, as it was completely abrogated by the addition of EGTA. More importantly, the engagement of the NKRP1A molecule induced interleukin (IL)-1 beta and IL-12 production by resting Mo and DC, respectively. Altogether these data indicate that NKRP1A lectin is present at the surface of Mo and DC and may play a relevant role in the activation and function of both cell types.

The role of matrix metalloproteinases in heart disease

The heart can be subdivided into cellular and extracellular compartments. Approximately one third of cells from this cellular compartment are cardiomyocytes whereas two thirds of the cells are non-cardiomyocytes. Because of their dimensions, cardiomyocytes occupy two thirds of the total myocardial volume. Non-myocytes, predominantly fibroblasts, endothelial cells and to a 1esSer extent mast cells, macrophages and smooth muscle cells in the media of the myocardial vasculature, together with the extracellular matrix and tissue fluid, fill the remaining one third of cardiac tissue. The extracellular matrix compartment consists of a structural network of interstitial type I and III fibrillar collagens, which have a high rigidity and are extremely resistant to proteolytic digestion [ 11. Besides the fibrillar collagen network, the extracellular compartment consists of basement membranes, which in the heart surround individual cardiomyocytes and smooth muscle cells, and separate endothelial cells, even in capillaries, from the media or surrounding connective tissue. Basement membranes contain a structural backbone of type IV collagen to which other components like laminins, fibronectin, heparan sulphate proteoglycan, and other extracellular matrix components can attach 121. Type V collagen has been localized in basement membranes and interspersed in the interstitium [3]. Type VI collagen was found predominantly between cardiomyo-cytes linking basement membranes of the individual myocytes to the surrounding extracellular matrix and interstitial cells. The cardiac extracellu-

EXPRESSION OF TRANSFORMING GROWTH FACTOR-ALPHA, EPIDERMAL GROWTH-FACTOR RECEPTOR AND PROLIFERATING CELL NUCLEAR ANTIGEN IN GASTRIC-CARCINOMA - AN IMMUNOHISTOCHEMICAL STUDY

Forty four cases of human gastric carcinoma were classified as either diffuse or intestinal in type. Serial sections of the paraffin-embedded tumours were stained with either monoclonal antibodies raised against transforming growth factor (TGF-alpha) or proliferating cell nuclear antigen (PCNA) or an affinity purified polyclonal antibody raised against the intracellular domain of the epidermal growth factor receptor (EGFR). Significantly higher levels of staining were found in the intestinal-type carcinomas with all three antibodies. When the extent of staining was arbitrarily divided into low (up to one third of cells stained), medium (one third to two thirds) or a high number of cells stained (two thirds to all of the cells), a much higher proportion (44%) of intestinal type tumours coexpressed TGF-alpha and EGFR to a medium or high level compared to the diffuse group (23%). In the intestinal-type tumours, though not in the diffuse-type tumours, this subgroup of tumours was associated with higher levels of PCNA staining. The relative lack of TGF-alpha or its receptor may be a significant factor in the histogenesis of diffuse gastric carcinoma, and in intestinal-type tumours the coexpression of TGF-alpha and EGFR may be part of an autocrine loop which stimulates the cells to divide.

CAMP-mediated expression of inwardly rectifying potassium channels in cultured mouse Schwann cells

Voltage-gated ionic currents were recorded from freshly dissociated or cultured mouse Schwann cells obtained from neonatal sciatic nerves by the whole-cell variation of the patch-clamp technique. Schwann cells virtually lost inwardly potassium (K ir) currents within 2 days after nerve transection or in culture conditions of neonatal sciatic nerves confirming the previous results that axonal signals were suggested to play an important role in the expression of functional K ir channels. To see the effects of adenosine 3′,5′-monophosphate (cAMP) analogues or forskolin on the expression of K ir channels in cultured Schwann cells, these agents were added to the culture medium 4 days after the start of the culture, when K ir currents were almost eliminated from cultured Schwann cells. Cultured Schwann cells restored the expression of K ir currents by co-culture with agents which elevate intracellular cAMP level. The dose-response of 8-(4-chlorophenylthio) (CPT) cAMP for the incidence of the expression of K ir currents showed a steep increase in the percentage of cells with K ir currents between 0.02 and 0.1 mM of external CPT cAMP and approximately two thirds of cells had K ir currents in higher concentrations of more than 0.1 mM of CPT cAMP after 4 days of incubation. After removal of CPT cAMP from the culture media after 4 days of incubation, K ir currents disappeared from cells within 2 days. The simultaneous application of cycloheximide (1 μg/ml), an inhibitor of protein synthesis, with CPT cAMP suppressed the expression of K ir currents for up to 6 days of incubation. After the cessation of cycloheximide treatment for 3 days, the expression of K ir currents were restored with a time lag of at least 3 days from the application of a cAMP analogue. These findings suggest that cAMP is an intracellular second messenger of axon-glial interactions for the expression of functional K ir channels in Schwann cells.

Elevation of cytosolic calcium by cholinoceptor agonists in SH-SY5Y human neuroblastoma cells: estimation of the contribution of voltage-dependent currents.

1. Muscarinic but not nicotinic receptor stimulation in SH-SY5Y human neuroblastoma cells induces a concentration-dependent increase in [3H]-inositol phosphate formation and a biphasic increase in [Ca2+]i. The latter involves release from both an intracellular store and Ca2+ entry across the plasma membrane. Here we examine the possibility that this agonist-stimulated Ca2+ entry occurs indirectly, as a consequence of depolarization. 2. Electrophysiological characterization, by whole cell patch-clamp techniques revealed that SH-SY5Y cells possess a tetrodotoxin-sensitive inward sodium current, a dihydropyridine-insensitive calcium current and an outward potassium current which was blocked by tetraethylammonium, 4-aminopyridine and intracellular caesium ions. The outward potassium current showed voltage-dependent activation and inactivation, similar to that seen for A-currents. 3. Application of nicotinic agonists evoked an inward current in cells voltage-clamped at negative holding potentials, but this current rectified, resulting in little or no outward current flow at positive potentials. The mean amplitude at a holding potential of -60 mV was -1.14 nA. Extrapolation of the current-voltage relation gave a reversal potential of +8 mV, indicative of a non-specific cationic permeability. 4. Application of muscarinic agonists had no detectable effect in most of the cells tested. However, in one third of cells studied, a small slowly activating inward current was observed. The mean amplitude of this current at a holding potential of -60 mV was -8.3 pA.5. This study confirms that SH-SY5Y cells possess voltage-dependent sodium, potassium and calcium currents. In addition, these cells are strongly depolarized by nicotinic agonists, which produce little change in [Ca2t]1. On the other hand, muscarinic agonists produce profound changes in [Ca2+1J with only a small inward current (depolarization). The contrasting effects of these two cholinoceptor agonists strongly implies that the Ca2+ entry after muscarinic receptor activation is not primarily due to activation of voltage-dependent calcium channels.

CAMP-mediated expression of inwardly rectifying potassium channels in cultured mouse Schwann cells

Abstract Voltage-gated ionic currents were recorded from freshly dissociated or cultured mouse Schwann cells obtained from neonatal sciatic nerves by the whole-cell variation of the patch-clamp technique. Schwann cells virtually lost inwardly potassium (K ir ) currents within 2 days after nerve transection or in culture conditions of neonatal sciatic nerves confirming the previous results that axonal signals were suggested to play an important role in the expression of functional K ir channels. To see the effects of adenosine 3′,5′-monophosphate (cAMP) analogues or forskolin on the expression of K ir channels in cultured Schwann cells, these agents were added to the culture medium 4 days after the start of the culture, when K ir currents were almost eliminated from cultured Schwann cells. Cultured Schwann cells restored the expression of K ir currents by co-culture with agents which elevate intracellular cAMP level. The dose-response of 8-(4-chlorophenylthio) (CPT) cAMP for the incidence of the expression of K ir currents showed a steep increase in the percentage of cells with K ir currents between 0.02 and 0.1 mM of external CPT cAMP and approximately two thirds of cells had K ir currents in higher concentrations of more than 0.1 mM of CPT cAMP after 4 days of incubation. After removal of CPT cAMP from the culture media after 4 days of incubation, K ir currents disappeared from cells within 2 days. The simultaneous application of cycloheximide (1 μg/ml), an inhibitor of protein synthesis, with CPT cAMP suppressed the expression of K ir currents for up to 6 days of incubation. After the cessation of cycloheximide treatment for 3 days, the expression of K ir currents were restored with a time lag of at least 3 days from the application of a cAMP analogue. These findings suggest that cAMP is an intracellular second messenger of axon-glial interactions for the expression of functional K ir channels in Schwann cells.

Ion channels activated by acetylcholine and γ-aminobutyric acid in freshly dissociated sympathetic neurones of the rat

Transmitter-activated channels in freshly isolated neurones from sympathetic ganglia of young rats have been examined using the patch-clamp technique. Acetylcholine (ACh), γ-aminobutyric acid (GABA) and (in about one third of cells) glycine produced an inward current and an increase in current noise when perfused onto voltage-clamped neurones. The ACh noise was fitted with a single Lorentzian spectrum with a time constant of 13.1 ms at − 70 mV. Outside-out membrane patches allowed high-resolution measurements of single ACh- and GABA-activated channels. The ACh-channels had a conductance of 30 pS.

Dynamics of orientational tuning of cat visual cortical neurons

Orientational tuning of primary visual cortical unit activity was investigated in acute experiments on cats immobilized by a muscle relaxant, by the time slices method. Poststimulus histograms of responses of a neuron to presentation of a flashing bar of light in the center of its receptive field, with different orientations, were plotted; graphs of orientational tuning with respect to mean discharge frequency in consecutive time cuts of the responses with a 10 or 20 msec step were then plotted. Orientational tuning in all cortical neurons studied exhibited considerable dynamic changes in sharpness and preferred orientation. In two thirds of cells an effect of scanning a certain part of the range of orientations was observed, in the form of a successive shift of the maximum of the orientational tuning curve from some preferred orientations to others was discovered. The possible functional significance of spike discharges of visual cortical neurons is discussed.

Directional tuning of complex cells in area 17 of the feline visual cortex.

1. Directional tuning for motion of a field of static visual noise and for motion of bar stimuli against the same stationary noise field as background was compared in eighty-four deep-layer complex cells recorded from area 17 of cats, lightly anaesthetized with N(2)O/O(2) supplemented with pentobarbitone. Detailed comparisons of monocular tuning for the dominant eye receptive field were made for seventy-two cells. Interocular, and stimulus-dependent ocular dominance differences are reported elsewhere (Hammond, 1978c, and in preparation).2. Directional bias for preferred and opposite directions of motion was enhanced with moving noise fields, compared with moving bar stimuli. Two thirds of cells directionally biased for bars, were directionally selective for noise (33/49); ten of these showed suppression of firing to noise moving in the ;null' direction. An additional twenty-three cells were directionally selective for bar stimuli and for noise, nine with suppression of firing in the null direction.3. A majority of cells (52/62) showed significant differences in preferred directions for bar stimuli and for noise; in an exceptional case, tuning for the two classes of stimuli was orthogonal. Tuning for bar stimuli was usually sharper than for noise. In cells asymmetrically tuned for bar stimuli, tuning was broader for the flank of the tuning curve closest to the preferred direction for noise. Ten cells showed similar tuning for bars and noise; tuning for the remaining ten cells was rather variable or poorly defined.22/62 cells showed bimodal directional tuning to noise, with depression of sensitivity over the range of directions to which the cell responded well with a moving bar stimulus.4. Cells were frequently more responsive to noise-field motion than to bar motion. Cells with large receptive fields showed greater sensitivity to noise than those with small fields, and were relatively more sensitive to noise than to bar stimuli.5. The results are interpreted as evidence that the directional and orientational sensitivity of complex cells are mediated by different mechanisms.

Spontaneous and synaptic excitation of paramedian reticular neurones in the decerebrate cat.

1. In decerebrate cats neurones in the region of the paramedian reticular nucleus were identified by responses to stimulation of implanted cerebellar electrodes. Approximately one half were antidromically activated and one half orthodromically. 2. Somatic stimulation and electrical stimulation of both hind limb and cranial nerves activated many of these cells. There was no correlation between the effects of these stimuli on cell firing and on blood pressure. 3. A number of rhythms in spontaneous firing were observed. One fifth of cells fired with the rhythm of efferent activity in the recurrent laryngeal nerve. In animals showing cycles of stability and instability in blood pressure corresponding phases of activity and inactivity in the firing of paramedian reticular neurones were observed. 4. Most paramedian reticular cells showed bursts of firing preceding abrupt rises in blood pressure but this was also observed with cells lateral to this area. 5. One third of cells studied showed changes in firing rate correlated with the changes in blood pressure which followed I.V. acetylcholine and noradrenaline. 6. Bilateral carotid artery occlusion, which always produced a rise in blood pressure, had little effect on cell firing.

Distribution of microtubules and microfilaments in developing vestibular sensory epithelium of mouse otocysts grown in vitro.

Otocysts explanted from 12th-gestation-day mice and maintained in organ culture under went a series of developmental changes which paralleled those that occurred in vivo and which resulted in the formation of a sensory epithelium of the vestibular type. At the time of explantation presumptive vestibular sensory epithelium consisted of cells that were undifferentiated, pseudostratified and rapidly proliferating. The only microtubules present were those of the mitotic apparatus. After 4 days of in vitro development cells comprising the presumptive vestibular sensory epithelium were less pseudostratified and more elongate; their nuclei had assumed a basal orientation and there was a clear maginal velum. Longitudinally oriented cytoplasmic microtubules were present at the apices of some cells; they were often grouped around a centriole which may have served as a nucleation centre for their assembly. After 7 days of in vitro development mitosis had ceased and supporting cells had innervated hair cells were present: both types of cells were always longer than they were broad and were often highly asymmetrical. Hair cells were flask- or columnar-shaped, with a nucleus situated in the basal third of the cell. Most mitochondria in hair cells were located in the apical third of the cell. The same distribution of mitochondria and nuclei was evident in supporting cells. Microtubules occurred throughout the length of the supporting cell and were always parallel to its longitudinal axis. In hair cells microtubules were more frequent than in supporting cells: the majority were parallel to the longitudinal axis of the cell but there were two exceptions. First, at the apex of hair cells some microtubules were oriented transversely and diagnonally: these were probably involved in the development and maintenance of the constricted apex of these cells. Secondly, microtubules appeared to be randomly arranged in the narrow region of the cytoplasm between the ventral surface of the nucleus and the base of the hair cells. Microfilaments were confined to the basal third of hair cells where their orientation paralleled that of microtubules. The possible functions of microtubules and microfilaments in the development of hair cells and supporting cells of the mouse vestibular epithelium are discussed.