The negative inotropic effect of raised extracellular potassium and caesium ions on isolated frog atrial trabeculae.
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.
Chapman
R A
RA
Department of Physiology, University of Leicester.
Rodrigo
G C
GC
D000200:Action Potentials; D000818:Animals; D002586:Cesium / Q000494:pharmacology*; D003864:Depression, Chemical; D006325:Heart Atria; D066298:In Vitro Techniques; D008564:Membrane Potentials; D009200:Myocardial Contraction / Q000187:drug effects*; D011188:Potassium / Q000494:pharmacology*; D011898:Ranidae / Q000378:metabolism*
D002586:Cesium; D011188:Potassium