Outer limiting membrane

Figure 14.1 Schematic diagram of the blood-retinal barrier (BRB). The retinal cell layers seen histologically consist of retinal pigment epithelium (RPE) photoreceptor outer segments (POS) outer limiting membrane (OLM) outer nuclear layer (ONL) outer plexiform layer (OPL) inner nuclear layer (INL) inner plexiform layer (IPL) ganglion cell layer (GCL) nerve fiber layer (NFL) inner limiting membrane (ILM).

The outer limiting membrane, which is not a true membrane but a narrow zone containing numerous zonulae adherentes between Muller cells, and betiveen Muller and the photoreceptor cells. 

Fig. 3. Confocal immunofluorescence showing RP2 localization in photoreceptors of the human retina. An 80-pm Vibratome section of human retina stained with rabbit hRP2-337-350 antiserum was detected with Cy3 conjugated donkey anti-rabbit and visualized by optical sectioning using a Zeiss LSM510 confocal microscope. OPL outer plexiform layer ONL outer nuclear layer OLM outer limiting membrane IS inner segment OS outer segment. Scale bar is 10 pm.

One of the most puzzling structures within C. parvum sporozoites, is the crystalloid body (CB), which is also in intimate contact with the relic mitochondrion, outer nuclear membrane, and RER (Fig. 1) (Keithly et al. 2005). Although it is still unclear whether this organelle is surrounded by a limiting membrane, or is simply a complex of closely packed membrane-bounded vesicles, it has been shown that like the relic mitochondrion, the CB takes up mitotracker dyes (Ctrnacta et al. 2006 Kayser et al. 2002 Keithly et al. 

TERS experiments were performed to study the bacterial cell surface. Biju et al. combined silver island films on glass coverslips with an AFM to investigate the effect of electron-acceptor limitation on the outer cell membrane of Shewanella one.ide.nsis [103]. 

A system underpinned by commercially made screen-printed electrochemical cells was described by Palmisano et al. [19]. The cells were converted into biosensors for lactate in milk and yoghurt by addition of an electrochemically polymerised barrier to interference and a layer composed of lactate oxidase, glutaraldehyde and BSA. These steps appeared to have been carried out by hand. As there was no outer diffusion-limiting membrane, the linear range of the sensors was quite small (0-0.7 mM). They were incorporated into a FIA with a microdialysis unit based on a planar membrane and a buffer reservoir (earlier work used a microdialysis fibre with a platinum electrode [29]. The concentration of lactate was determined in various milks (0.27-1.64 mM), and in raw milk (c. 0.5-0.9 mM) left to degrade on the laboratory bench. The recovery of the microdialysis unit, 2.6%, implied that the sensor had an ability to return measurable currents for very low concentrations of lactate. A further implication is that the electro-polymerised layer was very effective at preventing interference. 

Lamination (used by Patel et al. [18] above) is a fabrication technique that could be considered more widely by researchers in laboratories as an adjunct to screen-printing, particularly for deposition of outer diffusion-limiting membranes. Sensors can be constructed entirely by screen-printing technology [16], but it is difficult to maintain control over membrane thickness, porosity, etc. Deposition of pre-cast membranes by lamination may be a way of controlling these parameters more precisely. 

Polyurethanes have also been employed as outer sensor membranes. Yu et al. evaluated the biocompatibility and analytical performance of a subcutaneous glucose sensor with an epoxy-enhanced polyurethane outer membrane.15 The membrane was mechanically durable and the resulting sensors were functional for up to 56 days when implanted in the subcutaneous tissue of rats. Despite the improved sensor lifetime, all of the polyurethane-coated sensors were surrounded by a fibrous capsule, indicating an enduring inflammatory response that is undesirable due to the aforementioned effects on analytical sensor performance. To date, the clinical success of most passive approaches has been rather limited. It is doubtful that one passive material alone will be capable of imparting long-term (i.e., weeks to months) biocompatibility for in vivo use due to the extremely dynamic nature of the wound environment. 

The acrosome is a secretory granule that is assembled in spermatids by the coalescence of Golgi apparatus-derived vesicles. This process produces a large, membrane-limited organelle with an inner acrosomal membrane apposed to the nucleus, an outer acrosomal membrane subjacent to the plasmalemma, and an equatorial segment where these two membrane domains intersect. Our inability to obtain highly purified preparations of isolated acrosomes, despite earlier claims to the contrary (Hartree, 1977), has limited our understanding of the function of this or-... 

In muscle, most of the fatty acids undergoing beta oxidation are completely oxidized to C02 and water. In liver, however, there is another major fate for fatty acids this is the formation of ketone bodies, namely acetoacetate and b-hydroxybutyrate. The fatty acids must be transported into the mitochondrion for normal beta oxidation. This may be a limiting factor for beta oxidation in many tissues and ketone-body formation in the liver. The extramitochondrial fatty-acyl portion of fatty-acyl CoA can be transferred across the outer mitochondrial membrane to carnitine by carnitine palmitoyltransferase I (CPTI). This enzyme is located on the inner side of the outer mitochondrial membrane. The acylcarnitine is now located in mitochondrial intermembrane space. The fatty-acid portion of acylcarnitine is then transported across the inner mitochondrial membrane to coenzyme A to form fatty-acyl CoA in the mitochondrial matrix. This translocation is catalyzed by carnitine palmitoyltransferase II (CPTII Fig. 14.1), located on the inner side of the inner membrane. This later translocation is also facilitated by camitine-acylcamitine translocase, located in the inner mitochondrial membrane. The CPTI is inhibited by malonyl CoA, an intermediate of fatty-acid synthesis (see Chapter 15). This inhibition occurs in all tissues that oxidize fatty acids. The level of malonyl CoA varies among tissues and with various nutritional and hormonal conditions. The sensitivity of CPTI to malonyl CoA also varies among tissues and with nutritional and hormonal conditions, even within a given tissue. Thus, fatty-acid oxidation may be controlled by the activity and relative inhibition of CPTI. 

Iron uptake rates for most phytoplankton species appear to be limited by the rate of cross-membrane transport, itself a function of ligand exchange kinetics and the amount of space available on the outer cell membrane for transporter proteins... 

Diffusion-limited RET was also used to detomine the distance of the retinal from the outer disk membrane. In this case the diffusion-limited fransfer rate is given tty... 

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