Document Detail

Ionic and spectral mechanisms of the off response to light in hyperpolarizing photoreceptors of the clam, Lima scabra.
MedLine Citation:
PMID:  6325009     Owner:  NLM     Status:  MEDLINE    
Intracellular recordings were made from distal photoreceptor cells of the file clam Lima scabra in order to examine the ionic and spectral mechanisms which underly the response to light decrement. These receptors are primary sensory neurons that generate nerve impulses in the optic nerve upon light termination without benefit of synaptic interconnections between photoreceptor cells. Microelectrode measurements were made on these cells. Membrane conductance changes were assessed by measuring membrane voltage changes elicited under different conditions while passing constant-current pulses through the microelectrode from an active bridge amplifier. Responses of membrane potential in light and darkness in different concentrations of external potassium ions were fitted to a simplified form of the constant field equation. This analysis allowed an estimation of internal potassium activity (281 mM) as well as changes in PNa/PK in darkness and light. PNa/PK changed from 0.09 in darkness to 0.03 at the peak of the light response. A persistent decrease in membrane conductance at the termination of light is associated with a depolarization that overshoots the dark resting membrane potential. This transient depolarization is dependent on the intensity and duration of the preceding period of light. The amplitude of the dark-dependent depolarization is related to the absorbance of light during the preceding period of light by a long wavelength intermediate of rhodopsin bleaching (metarhodopsin). The frequency of discharge of action potentials with rapid kinetics which occurs following light is proportional to the amplitude of the after depolarizing response. The delay to onset of the discharge is inversely proportional to the amplitude of the after depolarizing response. The sensitivity (response/photon) of distal cells can be modified by background light which passes through a screening pigment found in cells that surround the eye. These data, taken together, provide an explanation for the persistent discharge of action potentials which occurs on termination of light in these cells as well as the visual cells of other gastropod mollusks.
M C Cornwall; A L Gorman
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Publication Detail:
Type:  Journal Article; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Cellular and molecular neurobiology     Volume:  3     ISSN:  0272-4340     ISO Abbreviation:  Cell. Mol. Neurobiol.     Publication Date:  1983 Dec 
Date Detail:
Created Date:  1984-06-13     Completed Date:  1984-06-13     Revised Date:  2008-11-21    
Medline Journal Info:
Nlm Unique ID:  8200709     Medline TA:  Cell Mol Neurobiol     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  311-28     Citation Subset:  IM; S    
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MeSH Terms
Bivalvia / physiology*
Color Perception / physiology*
Ion Channels / physiology*
Membrane Potentials
Neural Inhibition
Optic Nerve / physiology
Photic Stimulation
Photoreceptor Cells / physiology*
Potassium / metabolism
Retina / physiology
Rhodopsin / analogs & derivatives,  metabolism
Visual Perception / physiology*
Grant Support
Reg. No./Substance:
0/Ion Channels; 60383-01-9/metarhodopsins; 7440-09-7/Potassium; 9009-81-8/Rhodopsin

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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