Cargando…
The Ventral Photoreceptor Cells of Limulus : III. A voltage-clamp study
In the dark, the ventral photoreceptor of Limulus exhibits time-variant currents under voltage-clamp conditions; that is, if the membrane potential of the cell is clamped to a depolarized value there is an initial large outward current which slowly declines to a steady level. The current-voltage rel...
Autores principales: | , |
---|---|
Formato: | Texto |
Lenguaje: | English |
Publicado: |
The Rockefeller University Press
1969
|
Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2225933/ https://www.ncbi.nlm.nih.gov/pubmed/5806593 |
_version_ | 1782149741891551232 |
---|---|
author | Millecchia, Ronald Mauro, Alexander |
author_facet | Millecchia, Ronald Mauro, Alexander |
author_sort | Millecchia, Ronald |
collection | PubMed |
description | In the dark, the ventral photoreceptor of Limulus exhibits time-variant currents under voltage-clamp conditions; that is, if the membrane potential of the cell is clamped to a depolarized value there is an initial large outward current which slowly declines to a steady level. The current-voltage relation of the cell in the dark is nonlinear. The only ion tested which has any effect on the current-voltage relation is potassium; high potassium shifts the reversal potential towards zero and introduces a negative slope-conductance region. When the cell is illuminated under voltage-clamp conditions, an additional current, the light-induced current, flows across the cell membrane. The time course of this current mimics the time course of the light response (receptor potential) in the unclamped cell; namely, an initial transient phase is followed by a steady-state phase. The amplitude of the peak transient current can be as large as 60 times the amplitude of the steady-state current, while in the unclamped cell the amplitude of the peak transient voltage never exceeds 4 times the amplitude of the steady-state voltage. The current-voltage relations of the additional light-induced current obtained for different instants of time are also nonlinear, but differ from the current-voltage relations of the dark current. The ions tested which have the greatest effect on the light-induced current are sodium and calcium; low sodium decreases the current, while low calcium increases the current. The data strongly support the hypothesis that two systems of electric current exist in the membrane. Thus the total ionic current which flows in the membrane is accounted for as the sum of a dark current and a light-induced current. |
format | Text |
id | pubmed-2225933 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1969 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22259332008-04-23 The Ventral Photoreceptor Cells of Limulus : III. A voltage-clamp study Millecchia, Ronald Mauro, Alexander J Gen Physiol Article In the dark, the ventral photoreceptor of Limulus exhibits time-variant currents under voltage-clamp conditions; that is, if the membrane potential of the cell is clamped to a depolarized value there is an initial large outward current which slowly declines to a steady level. The current-voltage relation of the cell in the dark is nonlinear. The only ion tested which has any effect on the current-voltage relation is potassium; high potassium shifts the reversal potential towards zero and introduces a negative slope-conductance region. When the cell is illuminated under voltage-clamp conditions, an additional current, the light-induced current, flows across the cell membrane. The time course of this current mimics the time course of the light response (receptor potential) in the unclamped cell; namely, an initial transient phase is followed by a steady-state phase. The amplitude of the peak transient current can be as large as 60 times the amplitude of the steady-state current, while in the unclamped cell the amplitude of the peak transient voltage never exceeds 4 times the amplitude of the steady-state voltage. The current-voltage relations of the additional light-induced current obtained for different instants of time are also nonlinear, but differ from the current-voltage relations of the dark current. The ions tested which have the greatest effect on the light-induced current are sodium and calcium; low sodium decreases the current, while low calcium increases the current. The data strongly support the hypothesis that two systems of electric current exist in the membrane. Thus the total ionic current which flows in the membrane is accounted for as the sum of a dark current and a light-induced current. The Rockefeller University Press 1969-09-01 /pmc/articles/PMC2225933/ /pubmed/5806593 Text en Copyright © 1969 by The Rockefeller University Press This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/). |
spellingShingle | Article Millecchia, Ronald Mauro, Alexander The Ventral Photoreceptor Cells of Limulus : III. A voltage-clamp study |
title | The Ventral Photoreceptor Cells of Limulus
: III. A voltage-clamp study |
title_full | The Ventral Photoreceptor Cells of Limulus
: III. A voltage-clamp study |
title_fullStr | The Ventral Photoreceptor Cells of Limulus
: III. A voltage-clamp study |
title_full_unstemmed | The Ventral Photoreceptor Cells of Limulus
: III. A voltage-clamp study |
title_short | The Ventral Photoreceptor Cells of Limulus
: III. A voltage-clamp study |
title_sort | ventral photoreceptor cells of limulus
: iii. a voltage-clamp study |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2225933/ https://www.ncbi.nlm.nih.gov/pubmed/5806593 |
work_keys_str_mv | AT millecchiaronald theventralphotoreceptorcellsoflimulusiiiavoltageclampstudy AT mauroalexander theventralphotoreceptorcellsoflimulusiiiavoltageclampstudy AT millecchiaronald ventralphotoreceptorcellsoflimulusiiiavoltageclampstudy AT mauroalexander ventralphotoreceptorcellsoflimulusiiiavoltageclampstudy |