Polymer-Coated NaYF₄:Yb³⁺, Er³⁺ Upconversion Nanoparticles for Charge-Dependent Cellular Imaging

Lanthanide-doped upconversion nanoparticles (UCNPs) are considered promising novel near-infrared (NIR) bioimaging agents with the characteristics of high contrast and high penetration depth. However, the interactions between charged UCNPs and mammalian cells have not been thoroughly studied, and the corresponding intracellular uptake pathways remain unclear. Herein, our research work involved the use of a hydrothermal method to synthesize polyvinylpyrrolidone-coated UCNPs (UCNP-PVP), and then a ligand exchange reaction was performed on UCNP-PVP, with the help of polyethylenimine (PEI) and poly(acrylic acid) (PAA), to generate UCNP-PEI and UCNP-PAA. These polymer-coated UCNPs demonstrated good dispersibility in aqueous medium, had the same elemental composition and crystal phase, shared similar TEM and dynamic light scattering (DLS) size distribution, and exhibited similar upconversion luminescence efficiency. However, the positively charged UCNP-PEI evinced greatly enhanced cellular uptake in comparison with its neutral or negative counterparts, as shown by multiphoton confocal microscopy and inductively coupled plasma mass spectrometry (ICP-MS) measurements. Meanwhile, we found that cationic UCNP-PEI can be effectively internalized mainly through the clathrin endocytic mechanism, as revealed by colocalization, chemical, and genetic inhibitor studies. This study elucidates the role of the surface polymer coatings in governing UCNP–cell interactions, and it is the first report on the endocytic mechanism of positively charged lanthanide-doped UCNPs. Furthermore, this study provides important guidance for the development of UCNPs as specific intracellular nanoprobes, allowing us to control the UCNP–cell interactions by tuning surface properties

Effect of prolactin on the phosphorylation of Ca-dependent PKC isoforms

<p><b>Copyright information:</b></p><p>Taken from "Prolactin stimulates the proliferation of normal female cholangiocytes by differential regulation of Ca-dependent PKC isoforms"</p><p>http://www.biomedcentral.com/1472-6793/7/6</p><p>BMC Physiology 2007;7():6-6.</p><p>Published online 19 Jul 2007</p><p>PMCID:PMC1939715.</p><p></p> Immunoblots for PKC-α, PKC-β-I, PKC-β-II and PKC-γ in normal female cholangiocytes stimulated for 90 minutes at 37°C with 0.2% BSA (basal value) or prolactin (100 nM) with 0.2% BSA. When cholangiocytes were treated with prolactin, there was an increase in the phosphorylation of PKCβ-I and a marked decrease in PKCα phosphorylation; no significant changes in the phosphorylation of PKCβ-II and PKCγ were observed in normal female cholangiocytes treated with prolactin or 0.2% BSA. Data are mean ± SEM of 3 experiments. * p < 0.05 vs. corresponding basal values. PKC = protein kinase C

Measurement of the number of top panel PCNA- and lower panel CK-19-positive cholangiocytes in liver sections (5 μm, 3 slides analyzed per group) and c PCNA protein expression in purified female cholangiocytes from NaCl- or prolactin-treated rats

<p><b>Copyright information:</b></p><p>Taken from "Prolactin stimulates the proliferation of normal female cholangiocytes by differential regulation of Ca-dependent PKC isoforms"</p><p>http://www.biomedcentral.com/1472-6793/7/6</p><p>BMC Physiology 2007;7():6-6.</p><p>Published online 19 Jul 2007</p><p>PMCID:PMC1939715.</p><p></p> Administration of prolactin to normal female rats increased the number of PCNA-positive cholangiocytes (arrows) and CK-19-positive cholangiocytes compared with normal rats treated with NaCl. Orig. magn., ×20 (PCNA) and ×10 (CK-19). Data are mean ± SEM of 5 values obtained from the 3 slides evaluated per each group of animal. * p < 0.05 vs. the corresponding value of NaCl-treated rats