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rdf:type | |
lifeskim:mentions | |
pubmed:issue |
6
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pubmed:dateCreated |
1992-2-25
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pubmed:abstractText |
We have recorded changes of membrane current, intracellular Na+ activity (aiNa), intracellular pH (pHi) and the strength of contraction in voltage-clamped sheep Purkinje fibres during and after inhibition of the Na(+)-K+ pump. The pump was inhibited by the removal of K+ from the bathing solution and this resulted in a rise in aiNa. On return of K+ to the bathing medium to reactivate the Na(+)-K+ pump there was a fall of aiNa to below its control value after which aiNa slowly returned to its control value over the next 20 min. This 'undershoot' of aiNa was seen in 69% of contracting fibres and 78% of quiescent fibres, and the mean (+/- S.D.) values of the undershoot in contracting and quiescent fibres were 0.66 +/- 0.15 and 0.9 +/- 0.35 mM, respectively. The undershoot of aiNa was observed regardless of whether the Na(+)-K+ pump was reactivated with Rb+ or K+. It was not voltage dependent over the potential range studied (-95 to -45 mV) and was not accompanied by a change of intracellular pH. The undershoot of aiNa could be the result of a long-lasting increase in Na+ efflux or a long-lasting decrease in Na+ influx. Zero [K+]o resulted in the loss of one Na+ current, the pacemaker current i(f), but when K+ was returned to the bathing medium i(f) recovered rapidly and is therefore unlikely to be responsible for the long-lasting undershoot of aiNa. This conclusion was confirmed by the use of Cs+: although Cs+ blocked i(f), it did not block the undershoot of aiNa. The undershoot of aiNa was accompanied by (and, via Na(+)-Ca2+ exchange, was presumably the cause of) an undershoot of the force of contraction. Undershoots are not only seen after reactivation of the Na(+)-K+ pump: in a variety of different preparations, similar undershoots in aiNa and twitch force have been reported after a decrease in the frequency of stimulation. The undershoot of aiNa may be the result of novel feedback mechanism for the control of aiNa: the control of Na+ influx by aiNa.
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pubmed:grant | |
pubmed:language |
eng
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pubmed:journal | |
pubmed:citationSubset |
IM
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pubmed:chemical | |
pubmed:status |
MEDLINE
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pubmed:month |
Nov
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pubmed:issn |
0958-0670
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pubmed:author | |
pubmed:issnType |
Print
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pubmed:volume |
76
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pubmed:owner |
NLM
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pubmed:authorsComplete |
Y
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pubmed:pagination |
951-65
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pubmed:dateRevised |
2009-9-29
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pubmed:meshHeading |
pubmed-meshheading:1662968-Animals,
pubmed-meshheading:1662968-Cesium,
pubmed-meshheading:1662968-Feedback,
pubmed-meshheading:1662968-Hydrogen-Ion Concentration,
pubmed-meshheading:1662968-Kinetics,
pubmed-meshheading:1662968-Membrane Potentials,
pubmed-meshheading:1662968-Potassium,
pubmed-meshheading:1662968-Purkinje Fibers,
pubmed-meshheading:1662968-Sheep,
pubmed-meshheading:1662968-Sodium,
pubmed-meshheading:1662968-Sodium-Potassium-Exchanging ATPase
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pubmed:year |
1991
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pubmed:articleTitle |
Undershoots of intracellular sodium and the strength of contraction when the sodium-potassium pump of isolated sheep Purkinje fibres is reactivated by potassium.
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pubmed:affiliation |
Department of Physiology, University of Bristol.
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pubmed:publicationType |
Journal Article,
Research Support, Non-U.S. Gov't
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