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Adapting bump model for ventral photoreceptors of Limulus.
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MedLine Citation:
PMID:  7108487     Owner:  NLM     Status:  MEDLINE    
Abstract/OtherAbstract:
Light-evoked current fluctuations have been recorded from ventral photoreceptors of Limulus for light intensity from threshold up to 10(5) times threshold. These data are analyzed in terms of the adapting bump noise model, which postulates that (a) the response to light is a summation of bumps; and (b) the average size of bump decreases with light intensity, and this is the major mechanism of light adaptation. It is shown here that this model can account for the data well. Furthermore, the model provides a convenient framework to characterize, in terms of bump parameters, the effects of calcium ions, which are known to affect photoreceptor functions. From responses to very dim light, it is found that the average impulse response (average of a large number of responses to dim flashes) can be predicted from knowledge of both the noise characteristics under steady light and the dispersion of latencies of individual bumps. Over the range of light intensities studied, it is shown that (a) the bump rate increases in strict proportionality to light intensity, up to approximately 10(5) bumps per second; and (b) the bump height decreases approximately as the -0.7 power of light intensity; at rates greater than 10(5) bumps per second, the conductance change associated with the single bump seems to reach a minimum value of approximately 10(-11) reciprocal ohms; (c) from the lowest to the highest light intensity, the bump duration decreases approximately by a factor of 2, and the time scale of the dispersion of latencies of individual bumps decreases approximately by a factor of 3; (d) removal of calcium ions from the bath lengthens the latency process and causes an increase in bump height but appears to have no effect on either the bump rate or the bump duration.
Authors:
F Wong; B W Knight; F A Dodge
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  The Journal of general physiology     Volume:  79     ISSN:  0022-1295     ISO Abbreviation:  J. Gen. Physiol.     Publication Date:  1982 Jun 
Date Detail:
Created Date:  1982-10-12     Completed Date:  1982-10-12     Revised Date:  2009-11-18    
Medline Journal Info:
Nlm Unique ID:  2985110R     Medline TA:  J Gen Physiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  1089-113     Citation Subset:  IM    
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MeSH Terms
Descriptor/Qualifier:
Animals
Calcium / physiology
Horseshoe Crabs / physiology*
Light
Models, Biological*
Photoreceptor Cells / physiology*
Grant Support
ID/Acronym/Agency:
EY-0188/EY/NEI NIH HHS; EY-1428/EY/NEI NIH HHS
Chemical
Reg. No./Substance:
7440-70-2/Calcium
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From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

Full Text
Journal Information
Journal ID (nlm-ta): J Gen Physiol
ISSN: 0022-1295
ISSN: 1540-7748
Publisher: The Rockefeller University Press
Article Information
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Print publication date: Day: 1 Month: 6 Year: 1982
Volume: 79 Issue: 6
First Page: 1089 Last Page: 1113
ID: 2216452
Publisher Id: 82267838
PubMed Id: 7108487

Adapting bump model for ventral photoreceptors of Limulus


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