ABSTRACT
Polypyrrole (PPy) coated electrodes may provide new solutions to increase the charge injection capacity and biocompatibility of metal electrodes in e.g., neural stimulus applications. In this study, electrical impedance spectra of PPy coated platinum (Pt) electrodes having three different coating thicknesses were measured and modeled. A suitable equivalent electrical circuit providing the material characteristics was chosen and the impedance data was analyzed using the model and data fitting. The modeled parameter values of different coating thicknesses were compared and our results demonstrated the changes in charge transfer properties and mechanisms of thin and thick PPy film coatings.
Subject(s)
Biocompatible Materials/chemistry , Electronics , Platinum/chemistry , Polymers/chemistry , Pyrroles/chemistry , Electric Impedance , Electrodes , Microscopy, Atomic ForceABSTRACT
PURPOSE: Aquaporins (AQPs), a family of transmembrane water channel proteins, are essential for allowing passive water transport through retinal pigmented epithelial (RPE) cells. Even though human native RPE cells and immortalized human RPEs have been shown to express AQPs, the expression of AQPs during the differentiation in stem cell-derived RPE remains to be elucidated. METHODS: In human embryonic (hESCs) and induced pluripotent stem cells (hiPSCs)-derived RPE cells, the expression of several AQPs was determined by quantitative real-time PCR and the localization of AQP1 was assessed with confocal microscopy. The functionality of AQP water channels was determined by cell volume assay in hESC-derived RPE cells. RESULTS: AQP1, AQP3, AQP4, AQP5, AQP6, AQP7, AQP10, AQP11, and AQP12 were expressed in hESC- and hiPSC-derived RPE cells. Furthermore, the expression of AQP1 and AQP11 genes were significantly upregulated during the maturation of both hESC and iPSC into RPE. Confocal microscopy shows the expression of AQP1 at the apical plasma membrane of polarized cobblestone hESC- and hiPSC-derived RPE cells. Lastly, aquaporin inhibitors significantly reduced AQP functionality in hESC-RPE cells. CONCLUSIONS: hESC-RPE and hiPSC-RPE cells express several AQP genes, which are functional in mature hESC-derived RPE cells. The localization of AQP1 on the apical plasma membrane in mature RPE cells derived from both hESC and hiPSC suggests its functionality. These data propose that hESC- and hiPSC-derived RPE cells, grown and differentiated under serum-free conditions, resemble their native counterpart in the human eye.
Subject(s)
Aquaporins/genetics , Cell Differentiation/physiology , Embryonic Stem Cells/cytology , Gene Expression Regulation/physiology , Induced Pluripotent Stem Cells/cytology , Retinal Pigment Epithelium/cytology , Aquaporin 1/genetics , Aquaporin 1/metabolism , Aquaporins/metabolism , Biomarkers/metabolism , Cell Line , Cell Membrane/metabolism , Electric Impedance , Embryonic Stem Cells/metabolism , Eye Proteins/metabolism , Fluorescent Antibody Technique, Indirect , Glyceraldehyde-3-Phosphate Dehydrogenase (Phosphorylating)/metabolism , Homeodomain Proteins/metabolism , Humans , Induced Pluripotent Stem Cells/metabolism , Microphthalmia-Associated Transcription Factor/metabolism , Microscopy, Confocal , PAX6 Transcription Factor , Paired Box Transcription Factors/metabolism , RNA, Messenger/metabolism , Real-Time Polymerase Chain Reaction , Repressor Proteins/metabolism , Retinal Pigment Epithelium/metabolism , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
The barrier properties of epithelium are conventionally defined by transepithelial resistance (TER). TER provides information about the tightness of the epithelium. Electrical impedance spectroscopy (EIS) provides additional information regarding cell membrane properties, such as changes in electric capacitance and possible parallel or serial pathways that may correlate with the morphology of the cell layer. This study presents EIS of retinal pigment epithelial (RPE) cell model of the putative RPE differentiated from human embryonic stem cells (hESC-RPE). The generally utilized RPE cell model, ARPE-19, was used as immature control. The measured EIS was analyzed by fitting an equivalent electrical circuit model describing the resistive and capacitive properties of the RPE. Our results indicated that TER of hESC-RPE cells was close to the values of human RPE presented in the literature. This provides evidence that the stem cell-derived RPE in vitro can reach high-barrier function. Furthermore, hESC-RPE cells produced impedance spectra that can be modeled by the equivalent circuit of one time constant. ARPE-19 cells produced low-barrier properties, that is, an impedance spectra that suggested poor maturation of ARPE-19 cells. To conclude, EIS could give us means for non-invasively estimating the functionality and maturation of differentiated-RPE cells.
