Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina

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Publication Type Journal Article
School or College School of Medicine
Department Ophthalmology
Creator Normann, Richard A.
Other Author Perlman, Ido
Title Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina
Date 1990
Description 1. The effects of background illumination and bleached photopigment on luminosity type horizontal cells were studied in the isolated turtle retina. 2. Background illumination, which produced less than 60% bleaching, hyperpolarized and desensitized the horizontal cells to a degree which depended upon the background intensity. The desensitization of horizontal cells by these backgrounds is described by a Weber-Fechner type relationship. This desensitization primarily reflects the activation of a 'gain reduction' mechanism and cannot be accounted for by 'response compression'. 3. Following the termination of these backgrounds, horizontal cell sensitivity partially recovered but did not return to the pre-background, dark-adapted level. This desensitization was attributed to the presence of bleached photoproducts which were produced by the background exposure. 4. Application of very bright backgrounds caused the horizontal cells to initially hyperpolarize, and then to gradually depolarize towards the dark-adapted level along an exponential time course which appeared to reflect the decreased quantal catching associated with very high levels of photopigment bleaching. 5. From the time constant of the exponential decay of horizontal cell potential during the bright background illumination, the photosensitivity to bleaching of the cone photopigment was determined to be 4.5 x 10(7) effective quanta (633 nm) microns-2. 6. After termination of bright backgrounds which bleached more than 99% of the cone photopigment, the horizontal cell sensitivity increased linearly with time and after 25 min reached a level which was about 15% of the pre-background sensitivity. 7. Bleached photopigment reduces light sensitivity via at least two different mechanisms. For moderate degrees of bleaching (less than 95%), the presence of bleached photoproducts plays the major role in sensitivity control, producing a desensitization which is logarithmically related to the fraction of bleached pigment. During extensive bleaching (greater than 99%), the contribution of reduced quantal catching to sensitivity control becomes apparent and produces an additional loss in sensitivity which is linearly related to the fraction of unbleached pigment present.
Type Text
Publisher Cambridge University Press
First Page 321
Last Page 341
Subject Turtles; Retina; Photoreceptors; Bleached photopigment; Dark Adaptation
Subject MESH Turtles; Retina; Microscopy, Electron, Scanning
Language eng
Bibliographic Citation Normann RA, Perlman I. (1990). Background and bleaching adaptation in luminosity type horizontal cells in the isolated turtle retina. J Physiol, 421, 321-41
Rights Management © Cambridge University Press
Format Medium application/pdf
Identifier ir-main,12720
ARK ark:/87278/s6zs3f6b
Setname ir_uspace
Date Created 2012-06-13
Date Modified 2021-05-06
ID 707286
Reference URL
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