Light adaptation, photoreceptors

Figure 8. Stimulation of GC activity in ROS membranes by normal and mutant GCAPls as a function of Ca2+. The dark shaded area indicates low [Ca2+]ftee expected in the dark-adapted photoreceptors, the lighter shaded area reflects high [Ca2+]fKe expected in the light. Mutant GCAPls are active at Ca2+ concentrations which inactivate normal GCAP1 (See Colour Plate 8)...

Pugh, E.N., Jr., Nikonov, S., and Lamb, T.D. (1999). Molecular mechanisms of vertebrate photoreceptor light adaptation. Curr. Opin. Neurobiol. 9 410-418. 

Burkhardt DA (1994) Light adaptation and photopigment bleaching in cone photoreceptors in situ in the retina of the turtle. J Neurosci 14 1091-1105. 

Protocols for the measurement of light-adaptation kinetics that are based on the measurement of phototropic latencies are elaborate. These kinetics are much faster than the corresponding dark-adaptation kinetics. A characteristic feature of the kinetics for large steps up of the fluence rate is the fact that the level of adaptation appears to overshoot the actual fluence rate, a property that holds true for Phycomyces as well as ior Avena coleoptiles. " For oat seedlings, there is evidence that the processes that entail sensory adaptation are related to the phosphorylation of the putative photoreceptor."... 

Among the many sensory reactions Phycomyces displays, the study of the photoreceptor and adaptation deserves maximal attention, since Phycomyces shares these two attributes with a variety of other blue light sensitive organisms. Action-spectroscopy indicates a flavin as the photoreceptor of Phycomyces. /3-carotene was positively ruled out as a possible receptor, since mutants with no trace amounts of )3-carotene are phototropical normal. The photoreceptor has not yet been isolated. As in other systems the difficulty consists in distinguishing the flavin photoreceptor from the bulk flavoproteins in the cell. One therefore needs unambiguous criteria for the identification of the photoreceptor. The most promising approach for an isolation would be a photoreceptor mutant and we described the properties those mutants should have. Until now there is no firm evidence that the photomutants, madA or madB are defective in the photoreceptor. 

Visual photoreceptors have an ability to adapt to a wide range of light intensities 813... 

Fein, A. Excitation and adaptation of Limulus photoreceptors by light and inositol 1,4,5-triphosphate. Trends Neurosci. 9 110-114,1986. 

Bridges C 1959 The visual pigments of some common laboratory animals. Nature 184 727-728 Burns ME, Baylor DA 2001 Activation, deactivation, and adaptation in vertebrate photoreceptor cells. Annu Rev Neurosci 24 779-805 Cashmore AR, Jarillo JA, Wu Y-J, Liu D 1999 Cryptochromes blue light receptors for plants and animals. Science 284 760-765... 

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