principles and techniques of electron microscopy principles and techniques of electron microscopy electron microscopy and optics: general textbooks principles and techniques of electron microscopy principles and techniques of electron microscopy principles and techniques of digital holographic microscopy scanning electron microscopy cathodoluminescence of quartz introduction to transmission/scanning transmission principles and technique of fluorescence microscopy by m principles and techniques of electron microscopy: volume 1 principles of the phase contrast (electron) microscopy principles and techniques of electron microscopy lecture 1 the principles of microscopy principles in light microscopy scanning techniques in electron microscopy

Principles and Techniques of Electron Microscopy

Cytochemistry of Cell Glycoconjugates

Chlorins are attractive compounds for photodynamic therapy because of their high absorption in the red spectral region. In this study, the absorbance, fluorescence excitation and fluorescence emission spectra of chlorin e6 have been recorded as functions of pH in phosphate-buffered saline (PBS) solution with and without fetal calf serum (FCS). For pure PBS solutions, variation of the pH of the solution results in a shift of both the absorption and the fluorescence spectrum as well as in a decrease of the fluorescence intensity. Spectrophotometric and fluorimetric titration curves, based on observed changes, have been plotted. There is an indication of aggregate formation at low pH values (pH < 5). The presence of 5% FCS results in a shift of the titration curve, from an inflection point at about 6.5 to one at about 7.6. Pronounced spectral changes of the fluorescence emission spectra of protein-bound chlorin e6 (change of spectral shape, decrease of peak intensity) are also observed. The partition coefficients in the 1-octanol-water system increase with decreasing pH. Thus, relatively more of the drug is incorporated in the octanol phase at low pH. Cellular uptake of chlorin e6 in the presence of serum is significantly higher at pH 6.7 as compared with that at 7.3 and 7.6. We conclude that a change in the pH value of the surrounding medium leads to a change in the lipophilicity of chlorin e6. Such a change is likely to influence its binding to the serum proteins as well as its interaction with the plasma membrane of cells and may also be related to the selective tumor uptake of the drug.

Acid-base properties of chlorin e6: relation to cellular uptake.

Ultrastructural Cytochemistry of Blood Brain Barrier Endothelia

The morphologic features of cerebral endothelium that prevent large and small solutes from being transferred from blood to extravascular, interstitial fluid, are the complete belts of tight junctions between them and the low number of endocytotic invaginations in the luminal part of their cell membrane.15,108,131 When the capillaries of the central nervous system are perturbed in a number of unrelated ways, solutes can move from blood to brain tissue. The mechanisms of this transmural passage are still disputed. It is the intention of this chapter to review some firm and some preliminary evidence of (1) the ways in which endothelium may interact with the astrocyte in the establishment or maintenance of the barrier, (2) how the intact endothelium may selectively transfer specific ligands by receptor-mediated means, (3) the influence of electric charge on solute uptake by endothelium, (4) how the barrier may be circumvented, and (5) where extravasated solutes are disseminated interstitially.

The Anatomic Basis of the Blood-Brain Barrier

The surface charge of cultured neurons was investigated with the electron microscope markers anionized ferritin (AF) and cationized ferritin (CF). To determine which membrane components could react with the markers, model reactions were used. Both protein-coated Sepharose beads and lipid vesicles were reacted at physiological pH. Results with these model reactions indicate that the following groups may contribute to the surface charge: acidic groups--the sialic acid of both glycoproteins and gangliosides, the carboxyl group of proteins, and the phosphates of phospholipids; basic groups--the amines of proteins. The effect of chemical fixation on the surface charge was investigated. Glutaraldehyde fixation was shown to increase the charge of neutral proteins but not by a mechanism involving unbound aldehydes. Glutaraldehyde fixation of phospholipid vesicles in the presence of CF showed that amine-containing phospholipids were cross-linked to CF. This cross-linkage was seen with the electron microscope as the clumping of CF and the burying of CF in the membrane. Paraformaldehyde fixation had a lesser effect on the charge of proteins but did react with phospholipids as did glutaraldehyde. It is concluded that at physiological pH: (a) most of the charged proteins and lipids on cell surface can contribute to the membrane surface charge, and (b) the membrane surface charge of cells can be greatly changed by chemical fixation.

/pdf/contributions-of-lipids-and-proteins-to-the-surface-charge-566md3gkky.pdf

J G Wood

Papers

Contributions of lipids and proteins to the surface charge of membranes. An electron microscopy study with cationized and anionized ferritin.