Changes In Surface Distribution Research Articles

Equilibrium and kinetic modeling studies for copper and cadmium removal from aqueous solutions by ground nut husk

This study investigates the equilibrium and kinetics of copper and cadmium adsorption from aqueous solutions using groundnut husk. Characterization of the groundnut husk reveals various functional groups and a porous morphology. Isothermal studies were conducted, and different models were evaluated to fit the data. The Langmuir model exhibits the best fit for copper adsorption, while the Temkin and Dubinin–Radushkevich (DR) isotherm models show superior fitting for cadmium adsorption. Results suggest that physisorption significantly influences both cases, with mean sorption adsorption energy lower than 8000 J/mole. Error analysis reveals that the Freundlich and Temkin models demonstrate maximum adsorption capacity, with lower Chi-square (ꭓ2), Sum of Square Errors (SSE), and SAE compared to Langmuir and DR models. Additionally, intra-particle diffusion was analyzed using the Weber and Morris equation. Evaluation of model parameters indicates that cadmium demonstrates better nonlinear fitting of data compared to copper. FTIR and SEM analysis confirm the involvement of various functional groups in adsorption and reveal changes in surface distribution post-adsorption due to copper and cadmium presence.

The Transmembrane Domains of L-selectin and CD44 Regulate Receptor Cell Surface Positioning and Leukocyte Adhesion under Flow

During inflammation and immune surveillance, initial contacts (tethering) between free-flowing leukocytes and the endothelium are vitally dependent on the presentation of the adhesion receptor L-selectin on leukocyte microvilli. Determinants that regulate receptor targeting to microvilli are, however, largely elusive. Therefore, we systematically swapped the extracellular (EC), transmembrane (TM), and intracellular (IC) domains of L-selectin and CD44, a hyaluronan receptor expressed on the cell body and excluded from microvilli. Electron microscopy of transfected human myeloid K562 cells showed that the highly conserved TM domains are responsible for surface positioning. The TM segment of L-selectin forced chimeric molecules to microvilli, and the CD44 TM domain evoked expression on the cell body, whereas the IC and EC domains hardly influenced surface localization. Transfectants with microvillus-based chimeras showed a significantly higher adhesion rate under flow but not under static conditions compared with cells with cell body-expressed receptors. Substitution of the IC domain of L-selectin caused diminished tethering but no change in surface distribution, indicating that both microvillus positioning and cytoskeletal anchoring contribute to leukocyte tethering. These findings demonstrate that TM domains of L-selectin and CD44 play a crucial role in cell adhesion under flow by targeting receptors to microvilli or the cell body, respectively.

Targeting of voltage-gated potassium channel isoforms to distinct cell surface microdomains

Voltage-gated potassium (Kv) channels regulate action potential duration in nerve and muscle; therefore changes in the number and location of surface channels can profoundly influence electrical excitability. To investigate trafficking of Kv2.1, 1.4 and 1.3 within the plasma membrane, we combined the expression of fluorescent protein-tagged Kv channels with live cell confocal imaging. Kv2.1 exhibited a clustered distribution in HEK cells similar to that seen in hippocampal neurons, whereas Kv1.4 and Kv1.3 were evenly distributed over the plasma membrane. Using FRAP, surface Kv2.1 displayed limited mobility; approximately 40% of the fluorescence recovered within 20 minutes of photobleach (M(f)=0.41+/-0.04). Recovery occurred not by diffusion from adjacent membrane but probably by transport of nascent channel from within the cell. By contrast, the Kv1 family members Kv1.4 and Kv1.3 were highly mobile, both showing approximately 80% recovery (Kv 1.4 M(f)=0.78+/-0.07; Kv1.3 M(f)=0.78+/-0.04; without correction for photobleach); unlike Kv2.1, recovery was consistent with diffusion of channel from membrane adjacent to the bleach region. Studies using PA-GFP-tagged channels were consistent with the FRAP results. Following photoactivation of a small region of plasma membrane PA-GFP-Kv2.1 remained restricted to the photoactivation ROI, while PA-GFP-Kv1.4 rapidly diffused throughout the cell surface. Additionally, PA-GFP-Kv2.1 moved into regions of the cell membrane not adjacent to the original photoactivation ROI. Sucrose density gradient analysis indicated that half of Kv2.1 is part of a large, macromolecular complex while Kv1.4 sediments as predicted for the tetrameric channel complex. Disruption of membrane cholesterol by cyclodextrin minimally altered Kv2.1 mobility (M(f)=0.32+/-0.03), but significantly increased surface cluster size by at least fourfold. By comparison, the mobility of Kv1.4 decreased following cholesterol depletion with no change in surface distribution. The mobility of Kv1.3 was slightly increased following cyclodextrin treatment. These results indicate that (1) Kv2.1, Kv1.4 and Kv1.3 exist in distinct compartments that exhibit different trafficking properties, (2) membrane cholesterol levels differentially modulate the trafficking and localization of Kv channels and (3) Kv2.1 expressed in HEK cells exhibits a surface distribution similar to that seen in native cells.

Human vertebral cancellous bone surface distribution

The three-dimensional distribution of bone surface and the bone volume fraction (BV/TV) of 110 human vertebral cancellous bone specimens from seven individuals were measured using a three-dimensional radiographic method (microcomputed tomography). The ratios of the three principal projections of bone surface per total volume were found to be relatively constant for specimens examined in this study. The constancy of the projected surface ratios means that the fraction of the total bone surface oriented in any direction does not change markedly with BV/TV. Bone volume fraction was a good predictor of bone surface per total volume (BS/TV) for a one-parameter nonlinear model (r2 = 0.92). The results of this pilot study suggest that the changes in surface distribution which occur during age-related bone loss are largely predetermined rather than adaptive. The results are also consistent with the idea that cancellous bone tends to maintain a constant ratio of trabecular number for the principal directions. If these inferences from the data are correct, the morphogenetic processes which create the initial adult trabecular pattern become of primary interest. A model was developed which explained the strong relationship between BS/TV and BV/TV. The model was used to demonstrate the importance of morphogenetic processes.

Failure of climate regulation in a geophysiological model

THERE has been much debate about how the Earth responds to changes in climate—specifically, how feedbacks involving the biota change with temperature. There is in particular an urgent need to understand the extent of coupling and feedback between plant growth, global temperature and enhanced atmospheric concentrations of greenhouse gases. Here we present a simple, but we hope qualitatively realistic, analysis of the effects of temperature change on the feedbacks induced by changes in surface distribution of marine algae and land plants. We assume that algae affect climate primarily through their emission of dimethyl sulphide1–8 (which may influence cloud albedo), and that land plants do so by fixation of atmospheric CO2 (refs 9–12). When we consider how the planetary area occupied by these two ecosystems varies with temperature, we find that a simple model based on these ideas exhibits three feedback regimes. In glacial conditions, both marine and terrestrial ecosystems provide a negative feedback. As the temperature rises to present-day values, algae lose their strong climate influence, but terrestrial ecosystems continue to regulate the climate. But if global mean temperatures rise above about 20 °C, both terrestrial and marine ecosystems are in positive feedback, amplifying any further increase of temperature. As the latter conditions have existed in the past, we propose that other climate-regulating mechanisms must operate in this warm regime.