Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells
A subtype of retinal amacrine cells displayed a distinctive array of K(+) currents. Spontaneous miniature outward currents (SMOCs) were observed in the narrow voltage range of −60 to −40 mV. Depolarizations above approximately −40 mV were associated with the disappearance of SMOCs and the appearance...
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Formato: | Texto |
Lenguaje: | English |
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The Rockefeller University Press
2002
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Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311394/ https://www.ncbi.nlm.nih.gov/pubmed/11929886 http://dx.doi.org/10.1085/jgp.20028478 |
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author | Mitra, Pratip Slaughter, Malcolm M. |
author_facet | Mitra, Pratip Slaughter, Malcolm M. |
author_sort | Mitra, Pratip |
collection | PubMed |
description | A subtype of retinal amacrine cells displayed a distinctive array of K(+) currents. Spontaneous miniature outward currents (SMOCs) were observed in the narrow voltage range of −60 to −40 mV. Depolarizations above approximately −40 mV were associated with the disappearance of SMOCs and the appearance of transient (I(to)) and sustained (I(so)) outward K(+) currents. I(to) appeared at about −40 mV and its apparent magnitude was biphasic with voltage, whereas I(so) appeared near −30 mV and increased linearly. SMOCs, I(to), and a component of I(so) were Ca(2+) dependent. SMOCs were spike shaped, occurred randomly, and had decay times appreciably longer than the time to peak. In the presence of cadmium or cobalt, SMOCs with pharmacologic properties identical to those seen in normal Ringer's could be generated at voltages of −20 mV and above. Their mean amplitude was Nernstian with respect to [K(+)](ext) and they were blocked by tetraethylammonium. SMOCs were inhibited by iberiotoxin, were insensitive to apamin, and eliminated by nominally Ca(2+)-free solutions, indicative of BK-type Ca(2+)-activated K(+) currents. Dihydropyridine Ca(2+) channel antagonists and agonists decreased and increased SMOC frequencies, respectively. Ca(2+) permeation through the kainic acid receptor had no effect. Blockade of organelle Ca(2+) channels by ryanodine, or intracellular Ca(2+) store depletion with caffeine, eradicated SMOCs. Internal Ca(2+) chelation with 10 mM BAPTA eliminated SMOCs, whereas 10 mM EGTA had no effect. These results suggest a mechanism whereby Ca(2+) influx through L-type Ca(2+) channels and its subsequent amplification by Ca(2+)-induced Ca(2+) release via the ryanodine receptor leads to a localized elevation of internal Ca(2+). This amplified Ca(2+) signal in turn activates BK channels in a discontinuous fashion, resulting in randomly occurring SMOCs. |
format | Text |
id | pubmed-2311394 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2002 |
publisher | The Rockefeller University Press |
record_format | MEDLINE/PubMed |
spelling | pubmed-23113942008-04-21 Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells Mitra, Pratip Slaughter, Malcolm M. J Gen Physiol Article A subtype of retinal amacrine cells displayed a distinctive array of K(+) currents. Spontaneous miniature outward currents (SMOCs) were observed in the narrow voltage range of −60 to −40 mV. Depolarizations above approximately −40 mV were associated with the disappearance of SMOCs and the appearance of transient (I(to)) and sustained (I(so)) outward K(+) currents. I(to) appeared at about −40 mV and its apparent magnitude was biphasic with voltage, whereas I(so) appeared near −30 mV and increased linearly. SMOCs, I(to), and a component of I(so) were Ca(2+) dependent. SMOCs were spike shaped, occurred randomly, and had decay times appreciably longer than the time to peak. In the presence of cadmium or cobalt, SMOCs with pharmacologic properties identical to those seen in normal Ringer's could be generated at voltages of −20 mV and above. Their mean amplitude was Nernstian with respect to [K(+)](ext) and they were blocked by tetraethylammonium. SMOCs were inhibited by iberiotoxin, were insensitive to apamin, and eliminated by nominally Ca(2+)-free solutions, indicative of BK-type Ca(2+)-activated K(+) currents. Dihydropyridine Ca(2+) channel antagonists and agonists decreased and increased SMOC frequencies, respectively. Ca(2+) permeation through the kainic acid receptor had no effect. Blockade of organelle Ca(2+) channels by ryanodine, or intracellular Ca(2+) store depletion with caffeine, eradicated SMOCs. Internal Ca(2+) chelation with 10 mM BAPTA eliminated SMOCs, whereas 10 mM EGTA had no effect. These results suggest a mechanism whereby Ca(2+) influx through L-type Ca(2+) channels and its subsequent amplification by Ca(2+)-induced Ca(2+) release via the ryanodine receptor leads to a localized elevation of internal Ca(2+). This amplified Ca(2+) signal in turn activates BK channels in a discontinuous fashion, resulting in randomly occurring SMOCs. The Rockefeller University Press 2002-04 /pmc/articles/PMC2311394/ /pubmed/11929886 http://dx.doi.org/10.1085/jgp.20028478 Text en Copyright © 2002, 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 Mitra, Pratip Slaughter, Malcolm M. Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title | Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title_full | Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title_fullStr | Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title_full_unstemmed | Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title_short | Mechanism of Generation of Spontaneous Miniature Outward Currents (SMOCs) in Retinal Amacrine Cells |
title_sort | mechanism of generation of spontaneous miniature outward currents (smocs) in retinal amacrine cells |
topic | Article |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2311394/ https://www.ncbi.nlm.nih.gov/pubmed/11929886 http://dx.doi.org/10.1085/jgp.20028478 |
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