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Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration

We measured simultaneously in single toad rods the membrane photocurrent and the Ca concentration in a small volume surrounding the outer segment. Illumination causes a rise in the extracellular Ca concentration. Photocurrents and Ca concentration changes occur over the same range of light intensiti...

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Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1987
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228842/
https://www.ncbi.nlm.nih.gov/pubmed/3116153
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collection PubMed
description We measured simultaneously in single toad rods the membrane photocurrent and the Ca concentration in a small volume surrounding the outer segment. Illumination causes a rise in the extracellular Ca concentration. Photocurrents and Ca concentration changes occur over the same range of light intensities. Analysis of the time course of the Ca concentration changes suggests that these concentration changes arise from the difference in the transport rates of light-activated Ca influx and efflux across the outer segment plasma membrane. The Ca influx occurs through the light-sensitive channels of the outer segment membrane and the efflux through Na/Ca exchangers. In 0.1 mM external Ca, approximately 1-2% of the dark current is carried by Ca ions. The Ca efflux in the dark is identical to the influx, approximately 2 X 10(6) ions/s. Upon illumination, the Ca influx decreases with a time course and light sensitivity identical to those of the photocurrent. The Ca efflux, on the other hand, has very different kinetics from those of the photocurrent. Upon illumination, the Ca efflux decreases with a time course and light sensitivity determined by the change in membrane voltage and in the free cytoplasmic Ca concentration near the plasma membrane. In response to bright stimuli, which saturate the photocurrent for prolonged periods of time, the Ca efflux decays with an exponential time course from its value in darkness. The average time constant of this decay is 2.5 s. From the kinetics of the light- activated Ca fluxes, it is possible to predict that illumination causes a decrease in the cytoplasmic Ca concentration. We present a model of the regulation of the cytoplasmic Ca concentration by the dynamic balance of the Ca influx and efflux from the rod outer segment. The model accounts for our experimental observations and allows us to predict the time course and extent of the light-dependent decrease in the free cytoplasmic concentration.
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spelling pubmed-22288422008-04-23 Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration J Gen Physiol Articles We measured simultaneously in single toad rods the membrane photocurrent and the Ca concentration in a small volume surrounding the outer segment. Illumination causes a rise in the extracellular Ca concentration. Photocurrents and Ca concentration changes occur over the same range of light intensities. Analysis of the time course of the Ca concentration changes suggests that these concentration changes arise from the difference in the transport rates of light-activated Ca influx and efflux across the outer segment plasma membrane. The Ca influx occurs through the light-sensitive channels of the outer segment membrane and the efflux through Na/Ca exchangers. In 0.1 mM external Ca, approximately 1-2% of the dark current is carried by Ca ions. The Ca efflux in the dark is identical to the influx, approximately 2 X 10(6) ions/s. Upon illumination, the Ca influx decreases with a time course and light sensitivity identical to those of the photocurrent. The Ca efflux, on the other hand, has very different kinetics from those of the photocurrent. Upon illumination, the Ca efflux decreases with a time course and light sensitivity determined by the change in membrane voltage and in the free cytoplasmic Ca concentration near the plasma membrane. In response to bright stimuli, which saturate the photocurrent for prolonged periods of time, the Ca efflux decays with an exponential time course from its value in darkness. The average time constant of this decay is 2.5 s. From the kinetics of the light- activated Ca fluxes, it is possible to predict that illumination causes a decrease in the cytoplasmic Ca concentration. We present a model of the regulation of the cytoplasmic Ca concentration by the dynamic balance of the Ca influx and efflux from the rod outer segment. The model accounts for our experimental observations and allows us to predict the time course and extent of the light-dependent decrease in the free cytoplasmic concentration. The Rockefeller University Press 1987-09-01 /pmc/articles/PMC2228842/ /pubmed/3116153 Text en 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 Articles
Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title_full Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title_fullStr Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title_full_unstemmed Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title_short Kinetics of light-dependent Ca fluxes across the plasma membrane of rod outer segments. A dynamic model of the regulation of the cytoplasmic Ca concentration
title_sort kinetics of light-dependent ca fluxes across the plasma membrane of rod outer segments. a dynamic model of the regulation of the cytoplasmic ca concentration
topic Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2228842/
https://www.ncbi.nlm.nih.gov/pubmed/3116153