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| Predicate | Object |
|---|---|
| rdf:type | |
| lifeskim:mentions | |
| pubmed:dateCreated |
1983-1-7
|
| pubmed:abstractText |
1. The effects of low concentrations of Cs(+) (0.01-3mM) on the fully activated I-V relation ?(f)(E) for the pace-maker current in calf Purkinje fibres have been investigated. The action of Cs(+) is two-fold: in the negative region of the I-V curve Cs(+) induces a channel blockade; on the other hand, at more positive potentials Cs(+) can produce the opposite effect, i.e. a current increase.2. Cs(+)-induced blockade is concentration- and voltage-dependent, as observed on other cation channels. Data in the far negative voltage range (about - 150 to - 50 mV) can be fitted by a simple block model (Woodhull, 1973), which gives a mean value of 0.71 for the fraction of membrane thickness (delta) crossed by Cs(+) ions before reaching the blocking site. The value of delta does not appear to be affected by either external Na or external K concentrations. Values for the dissociation constant of the blocking reaction at E = 0 mV (k(0)) are found in the range 0.5-3.7 mM. In the positive region of the ?(f)(E) relation the current depression caused by channel blockade vanishes. Unexpectedly, in this range the current can be observed to increase with Cs(+), and ?(f)(E) curves in different Cs(+) concentrations show cross-over.3. Changing external K(+) also produces similar cross-over phenomena. Investigation of this effect reveals that the increase in slope of the I-V curve on raising the external K(+) concentration follows Michaelis-Menten kinetics, and can be interpteted in terms of K(+)-induced channel activation. It is found that 44+/-6 mM-K(+) half-saturates the channel activating reaction.4. The Cs(+)-induced current increase is large in low-K(+) solutions and vanishes in high-K(+) solutions, suggesting a competition between Cs(+) and K(+) ions in their activating action. Increasing Na(+) also limits the Cs(+)-induced current increase.5. Rb(+) also blocks the i(f) channel, though less efficiently than Cs(+). The block caused by Rb(+) is, unlike that of Cs(+), nearly voltage-independent, and is explained by assuming that the blocking reaction occurs near the external mouth of the channel (mean value of delta is 0.05). The zero-voltage dissociation constant (k(0)) of the Rb(+)-blocking reaction ranges between 1.4 and 5.4 mM, and is lower in low-Na(+), high-K(+) solutions.6. A possible characterization of the i(f) channel which explains these results includes an inner ;blocking' site, to which external Cs(+) ions bind, blocking the channel, and a more external ;activatory' site, to which K(+), Cs(+), Rb(+) and possibly Na(+) ions bind. Binding of K(+) to this site induces a current increase either by modulating the channel, or actually by opening the channel itself. A similar mechanism can apply to Cs(+) and to Rb(+) binding.
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| pubmed:commentsCorrections |
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-1202319,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-14241154,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-16073434,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-303350,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-308537,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-310542,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-4541078,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-4644327,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-4854650,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-5044577,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-5346528,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-543757,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-566793,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-6034758,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-6262501,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-6273533,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-6273534,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-650431,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-66317,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-6770079,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-722275,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-7260268,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-945323,
http://linkedlifedata.com/resource/pubmed/commentcorrection/6292407-988568
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| pubmed:language |
eng
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| pubmed:journal | |
| pubmed:citationSubset |
IM
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| pubmed:chemical | |
| pubmed:status |
MEDLINE
|
| pubmed:month |
Aug
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| pubmed:issn |
0022-3751
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| pubmed:author | |
| pubmed:issnType |
Print
|
| pubmed:volume |
329
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| pubmed:owner |
NLM
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| pubmed:authorsComplete |
Y
|
| pubmed:pagination |
485-507
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| pubmed:dateRevised |
2009-11-18
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| pubmed:meshHeading |
pubmed-meshheading:6292407-Animals,
pubmed-meshheading:6292407-Binding, Competitive,
pubmed-meshheading:6292407-Cattle,
pubmed-meshheading:6292407-Cesium,
pubmed-meshheading:6292407-Dose-Response Relationship, Drug,
pubmed-meshheading:6292407-Heart Conduction System,
pubmed-meshheading:6292407-Ion Channels,
pubmed-meshheading:6292407-Kinetics,
pubmed-meshheading:6292407-Membrane Potentials,
pubmed-meshheading:6292407-Potassium,
pubmed-meshheading:6292407-Purkinje Fibers,
pubmed-meshheading:6292407-Rubidium
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| pubmed:year |
1982
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| pubmed:articleTitle |
Block and activation of the pace-maker channel in calf purkinje fibres: effects of potassium, caesium and rubidium.
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| pubmed:publicationType |
Journal Article,
In Vitro
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