Photoreceptor characterization

In recent years, a less familiar technique has been found very useful as a nondestructive method of investigating transport properties of photoreceptors (these are used in nonimpact printers for electronically processed or stored information). The technique is called xerographic TOF (XTOF) and it can be conveniently employed in parallel with the conventional measurements for photoreceptor characterization. In this chapter, we will briefly consider both traditional and xerographic TOF. 

In contrast to the other, morphologically relevant photoreceptor phytochrome, no unequivocal assay is available for the bluelight photoreceptor. This makes its purification and molecular characterization extremely difficult. 

The ligands for the other forms of membrane-bound GC are less well characterized. In some cases the functions of these GC forms have not been identified. GC-D is expressed in olfactory sensory neurons but its function has not been determined. GC-E and GC-F are expressed in photoreceptor cells in the retina and play a role in phototransduction. GC-G is widely expressed in peripheral tissues and brain but its ligand binding domain is similar to that for GC-A/GC-B, suggesting that it may be regulated by an ANP/BNP-like ligand [34]. 

Mutations in rhodopsin and other photoreceptor proteins are linked to retinitis pigmentosa. Retinitis pigmentosa (RP) is a group of inherited retinopathies that affects about 1 in 4,000 humans [26], RP maybe classified into four types autosomal dominant (19%), autosomal recessive (19%),X-linked (8%) and allied diseases (54%). RP is characterized by loss of night vision in the early stage, followed by loss of peripheral vision. Chromosomal loci for numerous RP genes have been mapped and mutations characterized [27]. 

H hstract. Until recently, all ocular photoreception was attributed to the rods and cones of the retina. However, studies on mice lacking rod and cone photoreceptors (rdjrdcl), has shown that these mice can still use their eyes to detect light to regulate their circadian rhythms, suppress pineal melatonin, modify locomotor activity and modulate pupil size. In addition, action spectra for some of these responses have characterized a novel opsin/vitamin A-based photopigment with a 480nm. Electrophysiological... 

The rd rd cl mouse has provided a powerful model to characterize the ocular non-rod, non-cone photoreceptors of mammals using action spectrum techniques. The first completed action spectrum was for the pupillary light reflex PLR (Lucas et al 2001). The results demonstrated that the PLR in rd rdcl mice is driven by a single opsin/vitamin A-based photopigment with a 479 nm. The... 

Organic photoreceptors can be prepared in either a flexible web or drum format. Webs are usually prepared on polymer substrates, polyethylene tere-phthalate being the most common. The substrates are between 100 to 200 pm in thickness and coated with a conducting surface layer. The substrates often contain layers on the reverse side for reduced curl, static discharge prevention, and control of frictional characteristics. The web configuration is also widely used for laboratory studies. For drums, the substrate is a metal cylinder, usually Al. Recently, however, drums of a poly(phenylene sulfide) resin doped with conductive C black have been developed (Kawata and Hikima, 1996). Drums are widely used in low- and mid-volume applications. Drums, however, are not well suited for research purposes. Thus, the preparation and characterization of drum photoreceptors is usually related to a specific application. 

Xerographic discharge, which is a highly space-charge-perturbed process, is therefore characterized by significant dispersion in the arrival times of photoinjected carriers. In some cases, the transit times of the slowest carriers are 10 times or more than the transit times of the fast carriers. However, the slowest carriers, too, must exit the TL before the photoreceptor reaches the development zone, typically 0.3-1.0 s after exposure. In practice, carrier mobilities that significantly exceed 10 cm /V-s are desirable. 

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