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

Q J Exp Physiol. 1987 Oct;72(4):561-70. doi: 10.1113/expphysiol.1987.sp003097.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials
  • Animals
  • Cesium / pharmacology*
  • Depression, Chemical
  • Heart Atria
  • In Vitro Techniques
  • Membrane Potentials
  • Myocardial Contraction / drug effects*
  • Potassium / pharmacology*
  • Ranidae / metabolism*


  • Cesium
  • Potassium