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The negative inotropic effect of raised extracellular potassium and caesium ions on isolated frog atrial trabeculae.

Authors
Type
Published Article
Journal
Quarterly journal of experimental physiology (Cambridge, England)
Publication Date
Volume
72
Issue
4
Pages
561–570
Identifiers
PMID: 3423202
Source
Medline
License
Unknown

Abstract

The exposure of frog atrial trabeculae to Ringer solution containing an elevated K+ concentration, produces a depolarization of the membrane and a reduction of both the duration of the action potential and the strength of the heart beat. In voltage-clamped preparations, the effect of perfusion with K+-rich Ringer solution is threefold. First, a sustained inward current develops at the holding potential (-80 mV). Secondly, the contractions evoked by depolarizing clamp pulses are reduced: this effect which is greater upon the tonic phase of the contraction than the early phasic tension, is also seen to follow the addition of Cs+ ions to the bathing fluid; at equal concentrations K+ ions are the more effective. Thirdly, when measured with an ion-sensitive micro-electrode in ventricular trabeculae, the intracellular Na+ ion activity (aiNa) declines with a time course similar to the development of the negative inotropic effect. This suggests that the actions of raised [K+]o or [Cs+]o upon tension may be secondary to an effect on the movement of Na+ ions across the cell membrane, which by reducing aiNa may affect tension by way of the Na-Ca exchange.

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