THE NEGATIVE INOTROPIC EFFECT OF RAISED EXTRACELLULAR POTASSIUM AND CAESIUM IONS ON ISOLATED FROG ATRIAL TRABECULAE

• Published in: Experimental physiology 1987-10, Vol.72 (4), p.561-570
• Main Authors: Chapman, R. A., Rodrigo, Glenn C.
• Format: Article
• Language: English
• Subjects: Action Potentials; Animals; Biological and medical sciences; Cesium - pharmacology; Depression, Chemical; Fundamental and applied biological sciences. Psychology; Heart; Heart Atria; In Vitro Techniques; Membrane Potentials; Myocardial Contraction - drug effects; Potassium - pharmacology; Ranidae - metabolism; Vertebrates: cardiovascular system
• ISSN: 0958-0670; 0144-8757; 1469-445X
• 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 ( a i Na ) 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 a i Na may affect tension by way of the Na-Ca exchange.