Membrane layer visualization

When electromagnetic radiation with wavelengths between 800 and 400 nm hits the human retina, a chain of events is initiated which eventually results in the excitation of the visual nerve and the perception of light or colour in the brain. The molecular basis for this process is the photoreceptor protein rhodopsin, which forms part of the membrane layers inside the cone and rod cells of the retina. The... 

In addition to providing a direct visualization of ionic clusters, the discovery of the thin fluorine-rich layer may have important implications with regard to the liquid/vapor sorption of these materials. To be sure, the nature of this layer would depend on the specific liquid or vapor environment contacting the membrane surface. In particular, the molecular polarity of the environment and its influence on surface tension would be involved. The difference between the liquid water versus saturated water vapor sorption was mentioned in this report. Also, the contact angle experiments of Zawodzinski et al. 

Figure 33. Visualization of liquid water transport in an operating transparent PEFC (45 /rm membrane with EW < 1000 GDL, Toray paper TGPH 090 with 20 wt % PTFE loading with a microporous layer).

Retina The ten-layered nervous tissue membrane of the eye. It is continuous with the optic nerve and receives images of external objects and transmits visual impulses to the brain. Its outer surface is in contact with the choroid and the inner surface with the vitreous body. The outer-most layer is pigmented, whereas the inner nine layers are transparent. [NiH]... 

It has long been established that all cell membranes in the body are composed of a fundamental structure called plasma membrane. This boundary surrounds single cells such as epithelial cells. More complex membranes such as intestinal epithelium and skin, are composed of multiples of this fundamental structure, which has been visualized as a bimolecular layer of lipid molecules with a monolayer of protein adsorbed into each surface. Cell membranes are further interspersed with small pores that can be protein line channels through the lipid layer or, simply, spaces between the lipid molecules. In membranes composed of many cells, the spaces between the cells constimte another kind of membrane pores (2). 

The layer of water adjacent to the absorptive membrane of the enterocyte is essentially unstirred. It can be visualized as a series of water lamellas, each progressively more stirred from the gut wall toward the lumen bulk. For BCS class 2 compounds the rate of permeation through the brush border is fast and the diffusion across the unstirred water layer (UWL) is the rate-limiting step in the permeation process. The thickness of the UWL in human jejunum was measured and found to be over 500 pm [3]. Owing to its thickness and hydrophilicity, the UWL may represent a major permeability barrier to the absorption of lipophilic compounds. The second mechanism by which the UWL functions act as a barrier to drug absorption is its effective surface area. The ratio of the surface area of the UWL to that of the underlying brush border membrane is at least 1 500 [4], i.e., this layer reduces the effective surface area available for the absorption of lipophilic compounds and hence impairs its bioavailability. 

Note. The alumina membranes have 20-nm diameter pores on the upper face that quickly widen within 5 pm of the surface to 200 nm throughout the membrane. Thus one face has 20-nm pores and the other has 200-nm pores. The membranes are packed with the 20-nm pores facing upward, but the two faces cannot be easily distinguished visually. However, the clear polypropylene support ring is wider on the 20-nm pore side of the membrane, which is the side that will be coated with the conductive layer. 

Wu M, Holowka D, Craighead HG, Baird B. Visualization of plasma membrane compartmentalization with patterned lipid hi-layers. Proc. Natl. Acad. Sci. 2004 101 13798-13803. 

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