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THE NEGATIVE INOTROPIC EFFECT OF RAISED EXTRACELLULAR POTASSIUM AND CAESIUM IONS ON ISOLATED FROG ATRIAL TRABECULAE
Author(s) -
Chapman R. A.,
Rodrigo Glenn C.
Publication year - 1987
Publication title -
quarterly journal of experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0144-8757
DOI - 10.1113/expphysiol.1987.sp003097
Subject(s) - depolarization , chemistry , biophysics , inotrope , membrane potential , extracellular , potassium , ion , voltage clamp , beat (acoustics) , contraction (grammar) , tonic (physiology) , intracellular , calcium , medicine , biochemistry , biology , physics , organic chemistry , acoustics
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.