THE EFFECTS OF POTASSIUM, AMMONIUM, CALCIUM, STRONTIUM AND MAGNESIUM ON THE ELECTROGRAM AND MYOGRAM OF MAMMALIAN HEART MUSCLE

¹ Department of Pharmacology, Cornell University Medical College, New York 21, N. Y.

The effects of five cations on the electrogram and myogram of mammalian heart muscle were studied, using the papillary muscle preparation. Increasing potassium concentration produced an inversion of the T deflection, widening of the R deflection and diminution of systolic force. Removal of potassium resulted in a repetitive response to each electrical stimulus. Ammonium ion increased contractile force, and widened the R deflection and the R-T interval.

Increasing the concentration of calcium increased the force of contraction and inverted the T deflection. Decreasing the concentration of calcium decreased the force of contraction without affecting the electrogram until, at a calcium level at which no contractile force could be recorded, the R-T interval decreased, and the R-T segment became elevated.

Strontium added to a solution containing the usual amount of calcium had an effect indistinguishable from that produced by adding an equimolar amount of calcium. However, when strontium was added to a solution low in calcium, it produced widening of the R-T interval and prolongation of systole. These effects were abolished by adding calcium.

Magnesium had no demonstrable effect on either myogram or electrogram.