Relationship of Changes in Ionic Concentrations to the Augmentation Produced by Extra Contractions in Isolated Mammalian Ventricular Muscle

Abstract

Studies performed on the isolated cat papillary muscle show that at calcium levels which reduce to about one-half the force of regularly spaced contractions, the extent of augmentation produced by a single interpolated beat is unchanged. Increase in potassium concentration produced a slight decrease in the augmentation effect. Variation in magnesium concentration had no effect. Changes from bicarbonate to phosphate buffer lowered the force of the regularly spaced contractions but did not change the degree of augmentation. It appears that the augmentation phenomenon probably cannot be explained on the basis of loss of intracellular potassium.