Phase portraits of dystrophic and nondystrophic mouse muscle-fiber action potentials

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

Intracellular action potentials from normal, control nondystrophic and dystrophic mouse soleus muscle fibers were recorded in both voltage-time and phase-portrait plots. Flattening of a normally curved portion in certain dystrophic muscle-fiber phase portraits suggested a greater than usual secondary entry of sodium ions after the peak of the action potential. Low-chloride studies excluded an abnormal chloride current as the cause of the flattening. It appears that inactivation of sodium ion conductance may be delayed or reduced, or both, in certain fibers of mice with hereditary muscular dystrophy. This is consistent with a general increase in membrane permeability. No definite negative afterpotential was noted in most mouse muscle-fiber action potentials.

Key Words: phase plane • phase plane trajectory • hereditary muscular • dystrophy • secondary sodium influx • cable equation • sodium inactivation • cell membrane permeability

Submitted on July 13, 1964