| Light responses and light adaptation in rat retinal rods at different temperatures. | |
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MedLine Citation:
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PMID: 16037091 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Rod responses to brief pulses of light were recorded as electroretinogram (ERG) mass potentials across isolated, aspartate-superfused rat retinas at different temperatures and intensities of steady background light. The objective was to clarify to what extent differences in sensitivity, response kinetics and light adaptation between mammalian and amphibian rods can be explained by temperature and outer-segment size without assuming functional differences in the phototransduction molecules. Corresponding information for amphibian rods from the literature was supplemented by new recordings from toad retina. All light intensities were expressed as photoisomerizations per rod (Rh*). In the rat retina, an estimated 34% of incident photons at the wavelength of peak sensitivity caused isomerizations in rods, as the (hexagonally packed) outer segments measured 1.7 microm x 22 microm and had specific absorbance of 0.016 microm(-1) on average. Fractional sensitivity (S) in darkness increased with cooling in a similar manner in rat and toad rods, but the rat function as a whole was displaced to a ca 0.7 log unit higher sensitivity level. This difference can be fully explained by the smaller dimensions of rat rod outer segments, since the same rate of phosphodiesterase (PDE) activation by activated rhodopsin will produce a faster drop in cGMP concentration, hence a larger response in rat than in toad. In the range 15-25 degrees C, the waveform and absolute time scale of dark-adapted dim-flash photoresponses at any given temperature were similar in rat and toad, although the overall temperature dependence of the time to peak (t(p)) was somewhat steeper in rat (Q(10) approximately 4 versus 2-3). Light adaptation was similar in rat and amphibian rods when measured at the same temperature. The mean background intensity that depressed S by 1 log unit at 12 degrees C was in the range 20-50 Rh* s(-1) in both, compared with ca 4500 Rh* s(-1) in rat rods at 36 degrees C. We conclude that it is not necessary to assume major differences in the functional properties of the phototransduction molecules to account for the differences in response properties of mammalian and amphibian rods. |
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Authors:
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S Nymark; H Heikkinen; C Haldin; K Donner; A Koskelainen |
Publication Detail:
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Type: Comparative Study; In Vitro; Journal Article; Research Support, Non-U.S. Gov't Date: 2005-07-21 |
Journal Detail:
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Title: The Journal of physiology Volume: 567 ISSN: 0022-3751 ISO Abbreviation: J. Physiol. (Lond.) Publication Date: 2005 Sep |
Date Detail:
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Created Date: 2005-09-16 Completed Date: 2005-12-23 Revised Date: 2009-11-18 |
Medline Journal Info:
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Nlm Unique ID: 0266262 Medline TA: J Physiol Country: England |
Other Details:
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Languages: eng Pagination: 923-38 Citation Subset: IM |
Affiliation:
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Laboratory of Biomedical Engineering, Helsinki University of Technology, Finland. soile.nymark@hut.fi |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Adaptation, Ocular
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physiology* Animals Barium / pharmacology Bufo bufo Cyclic GMP Electroretinography Light Models, Biological Rats Rats, Wistar Retinal Rod Photoreceptor Cells / physiology* Rod Cell Outer Segment / physiology Temperature* |
| Chemical | |
Reg. No./Substance:
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7440-39-3/Barium; 7665-99-8/Cyclic GMP |
| Comments/Corrections | |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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