Action of salicylate ions on the electrical properties of sheep cardiac Purkinje fibres.

Abstract

In sheep Purkinje fiber preparations salicylate ions produce reversible changes in resting potential and in action potential duration. In most preparations the effects resemble those produced by low extracellular K concentration: the resting potential first increases and then decreases, the action potential is prolonged and, eventually, low potential oscillations occur in the plateau range. In a few preparations action potential shortening occurs. The threshold current for initiating action potentials by an intracellular electrode is reversibly increased by salicylate. The activation curve, s.infin. (Em), for the pacemaker K current [iK2], shifted in a hyperpolarizing direction. The magnitude of the shift is .apprxeq. -5 mV in 5 mM-salicylate and -30 mV in 50 mM-salicylate. The apparent reversal potential for [iK2] is shifted in a negative direction. The magnitude of this shift at a given salicylate concentration varies with the K concentration. In an extracellular K concentration of 2.7 mM an average shift of -18 mV occurs in 10 mM salicylate; in 8 mM the average shift is -1 mV. Most of these effects may be produced by an increase in surface negative potential produced by the binding of salicylate to the cell membrane. This would produce the hyperpolarizing shift of activation curves for ionic current and, by increasing surface K activity, may lead to stimulation of the Na-K pump to produce an increase in the K gradient across the cell membrane.