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Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers
Stimulation of sarcoplasmic reticulum Ca release by Mg reduction of caffeine was studied in situ, to characterize further the Ca2+ dependence observed previously with stimulation by Cl ion. 45Ca efflux and isometric force were measured simultaneously at 19 degrees C in frog skeletal muscle fibers sk...
Formato: | Texto |
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Lenguaje: | English |
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The Rockefeller University Press
1981
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2215418/ https://www.ncbi.nlm.nih.gov/pubmed/6264018 |
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collection | PubMed |
description | Stimulation of sarcoplasmic reticulum Ca release by Mg reduction of caffeine was studied in situ, to characterize further the Ca2+ dependence observed previously with stimulation by Cl ion. 45Ca efflux and isometric force were measured simultaneously at 19 degrees C in frog skeletal muscle fibers skinned by microdissection; EGTA was added to chelate myofilament space Ca either before or after the stimulus. Both Mg2+ reduction (20 or 110 microM to 4 microM) and caffeine (5 mM) induced large force responses and 45Ca release, which were inhibited by pretreatment with 5 mM EGTA. In the case of Mg reduction, residual efflux stimulation was undetectable, and 45Ca efflux in EGTA at 4 microM Mg2+ was not significantly increased. Residual caffeine stimulation at 20 microM Mg2+ was substantial and was reduced further in increased EGTA (10 mM); at 600 microM Mg2+, residual stimulation in 5 mM EGTA was undetectable. Caffeine appears to initiate a small Ca2+- insensitive efflux that produces a large Ca2+-dependent efflux. Additional experiments suggested that caffeine also inhibited influx. The results suggest that stimulated efflux is mediated mainly or entirely by a channel controlled by an intrinsic Ca2+ receptor, which responds to local [Ca2+] in or near the channel. Receptor affinity for Ca2+ probably is influenced by Mg2+, but inhibition is weak unless local [Ca2+] is very low. |
format | Text |
id | pubmed-2215418 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1981 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22154182008-04-23 Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers J Gen Physiol Articles Stimulation of sarcoplasmic reticulum Ca release by Mg reduction of caffeine was studied in situ, to characterize further the Ca2+ dependence observed previously with stimulation by Cl ion. 45Ca efflux and isometric force were measured simultaneously at 19 degrees C in frog skeletal muscle fibers skinned by microdissection; EGTA was added to chelate myofilament space Ca either before or after the stimulus. Both Mg2+ reduction (20 or 110 microM to 4 microM) and caffeine (5 mM) induced large force responses and 45Ca release, which were inhibited by pretreatment with 5 mM EGTA. In the case of Mg reduction, residual efflux stimulation was undetectable, and 45Ca efflux in EGTA at 4 microM Mg2+ was not significantly increased. Residual caffeine stimulation at 20 microM Mg2+ was substantial and was reduced further in increased EGTA (10 mM); at 600 microM Mg2+, residual stimulation in 5 mM EGTA was undetectable. Caffeine appears to initiate a small Ca2+- insensitive efflux that produces a large Ca2+-dependent efflux. Additional experiments suggested that caffeine also inhibited influx. The results suggest that stimulated efflux is mediated mainly or entirely by a channel controlled by an intrinsic Ca2+ receptor, which responds to local [Ca2+] in or near the channel. Receptor affinity for Ca2+ probably is influenced by Mg2+, but inhibition is weak unless local [Ca2+] is very low. The Rockefeller University Press 1981-04-01 /pmc/articles/PMC2215418/ /pubmed/6264018 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 Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title | Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title_full | Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title_fullStr | Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title_full_unstemmed | Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title_short | Ca2+ dependence of stimulated 45Ca efflux in skinned muscle fibers |
title_sort | ca2+ dependence of stimulated 45ca efflux in skinned muscle fibers |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2215418/ https://www.ncbi.nlm.nih.gov/pubmed/6264018 |