Phase portraits of normal mouse muscle-fiber action potentials in high calcium

¹ Department of Physiology, College of Medicine, University of Iowa, Iowa City, Iowa

Action potentials were obtained from normal mouse soleus fibers immersed in high-calcium Ringer solutions and were recorded on a dual-beam oscilloscope as simultaneous voltage-time and phase-portrait plots. High calcium produced alterations resembling those noted in action potentials from mice with muscular dystrophy. Additional changes due to altered sodium activation and potassium activation were also present; since they occurred after the dystrophic-like alterations during the action potential and were not present in dystrophic mouse fiber records, it was concluded that a delayed potassium activation and current could not be responsible for the dystrophic-like changes. The data support a previously proposed hypothesis that dystrophic muscles have an increased secondary sodium influx during activity.

Key Words: phase plane • phase plane trajectory • secondary sodium influx • hereditary muscular dystrophy • sodium • inactivation • dystrophic mice • skeletal muscle

Submitted on July 24, 1964