Journal of photochemistry and photobiology. B, Biology
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J. Photochem. Photobiol. B, Biol. · Jul 2008
Reflected solar radiation from horizontal, vertical and inclined surfaces: ultraviolet and visible spectral and broadband behaviour due to solar zenith angle, orientation and surface type.
Ultraviolet (UV) radiation affects human life and UV exposure is a significant everyday factor that individuals must be aware of to ensure minimal damaging biological effects to themselves. UV exposure is affected by many complex factors. Albedo is one factor, involving reflection from flat surfaces. ⋯ The results show that the RRG due to a vertical surface can exceed the RRG due to a horizontal surface, at smaller solar zenith angles as well as large solar zenith angles. The RRG shows variability in reflective capacities of surface according to the above mentioned factors and present a more realistic influence on UV exposure than albedo for future investigations. Errors in measuring the RRG at large solar zenith angles are explored, which equally highlights the errors in albedo measurement at large solar zenith angles.
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J. Photochem. Photobiol. B, Biol. · Aug 1996
Dawn, diacylglycerol, calcium, and protein kinase C--the retinal wrecking crew. A signal transduction cascade for rhabdom shedding in the Limulus eye.
Vertebrate and invertebrate photoreceptors shed their photosensitive membrane on a daily basis. Although we have detailed knowledge of the morphology of the disc shedding and renewal process in vertebrate photoreceptors, and of the turnover of rhabdom in invertebrate photoreceptors, we know relatively little about the molecular mechanisms whereby these processes are triggered by light and/or by circadian efferent input to the retina. We have used the horseshoe crab, Limulus polyphemus, as a model system to unravel the molecular means by which the trigger light is communicated to the intracellular machinery responsible for the daily breakdown of the photosensitive membrane. ⋯ However, injecting inositol trisphosphate (InsP3) and DAG analog simultaneously results in a tenfold decrease in the concentration of DAG analog required to initiate a shedding event. Immunohistochemical screening for PKC in the lateral eye shows that two isozymes (PKC beta II and PKC zeta) are co-localized to the retinular cell rhabdom. Taken together, these data suggest that light triggers rhabdom shedding at dawn via a classical Ca(2+)-sensitive PKC, similar to PKC beta II, which is activated synergistically by the light-evoked production of DAG and InsP3.