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Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca
Na-Ca exchange current was measured at various concentrations of internal Na [( Na]i) and Ca [( Ca]i) using intracellular perfusion technique and whole-cell voltage clamp in single cardiac ventricular cells of guinea pig. Internal Ca has an activating effect on Nai-Cao exchange beginning at approxim...
Formato: | Texto |
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Lenguaje: | English |
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The Rockefeller University Press
1989
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2216252/ https://www.ncbi.nlm.nih.gov/pubmed/2549177 |
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collection | PubMed |
description | Na-Ca exchange current was measured at various concentrations of internal Na [( Na]i) and Ca [( Ca]i) using intracellular perfusion technique and whole-cell voltage clamp in single cardiac ventricular cells of guinea pig. Internal Ca has an activating effect on Nai-Cao exchange beginning at approximately 10 nM and saturating at approximately 50 nM with a half maximum [Ca]i (Km[Ca]i) of 22 nM (Hill coefficient, 3.7). Measurement of Nai-Cao exchange current at various concentration of [Na]i revealed an apparent Km[Na]i of 20.7 +/- 6.9 mM (n = 14) with imax of 3.5 +/- 1.2 microA/microF. For [Ca]i transported by the exchange, a Km[Ca]i of 0.60 +/- 0.24 microM (n = 8) with an imax of 3.0 +/- 0.54 microA/microF was obtained by measuring Nao-Cai exchange current. These values are apparently different from the values for the external binding site which have been reported previously. Whether Na and Ca compete for the external binding site, and if so, how it affects the binding constants was then investigated. Outward Nai-Cao exchange current became larger by reducing [Na]o. The double reciprocal plot of the current magnitude and [Ca]o at different [Na]o revealed a competitive interaction between Na and Ca. In the absence of competitor [Na]o, an apparent Km[Ca]o of 0.14 mM was obtained. When comparing internal and external Km values, the external value is markedly larger than the internal one and thus we conclude that binding sites of the Na- Ca exchange molecule are at least apparently asymmetrical between the inside and outside of the membrane. |
format | Text |
id | pubmed-2216252 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 1989 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-22162522008-04-23 Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca J Gen Physiol Articles Na-Ca exchange current was measured at various concentrations of internal Na [( Na]i) and Ca [( Ca]i) using intracellular perfusion technique and whole-cell voltage clamp in single cardiac ventricular cells of guinea pig. Internal Ca has an activating effect on Nai-Cao exchange beginning at approximately 10 nM and saturating at approximately 50 nM with a half maximum [Ca]i (Km[Ca]i) of 22 nM (Hill coefficient, 3.7). Measurement of Nai-Cao exchange current at various concentration of [Na]i revealed an apparent Km[Na]i of 20.7 +/- 6.9 mM (n = 14) with imax of 3.5 +/- 1.2 microA/microF. For [Ca]i transported by the exchange, a Km[Ca]i of 0.60 +/- 0.24 microM (n = 8) with an imax of 3.0 +/- 0.54 microA/microF was obtained by measuring Nao-Cai exchange current. These values are apparently different from the values for the external binding site which have been reported previously. Whether Na and Ca compete for the external binding site, and if so, how it affects the binding constants was then investigated. Outward Nai-Cao exchange current became larger by reducing [Na]o. The double reciprocal plot of the current magnitude and [Ca]o at different [Na]o revealed a competitive interaction between Na and Ca. In the absence of competitor [Na]o, an apparent Km[Ca]o of 0.14 mM was obtained. When comparing internal and external Km values, the external value is markedly larger than the internal one and thus we conclude that binding sites of the Na- Ca exchange molecule are at least apparently asymmetrical between the inside and outside of the membrane. The Rockefeller University Press 1989-06-01 /pmc/articles/PMC2216252/ /pubmed/2549177 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 Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title | Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title_full | Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title_fullStr | Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title_full_unstemmed | Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title_short | Sodium-calcium exchange current. Dependence on internal Ca and Na and competitive binding of external Na and Ca |
title_sort | sodium-calcium exchange current. dependence on internal ca and na and competitive binding of external na and ca |
topic | Articles |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2216252/ https://www.ncbi.nlm.nih.gov/pubmed/2549177 |