Charge movement and membrane capacity in frog muscle

1. The transient current required to impose a step charge of potential has a complex time course especially in the region of internal potential between -50 and -40 mV. 2. Examination of non-linear transient current in this voltage range suggests two components of charge movement: (a) an initial more-or-less exponential movement, and (b) a slower component with a complex time course. 3. Measurements of membrane capacity support such a division and confirm the steeper voltage dependence of the slower charge movement. 4. Permanent depolarization to 40 mV appears to immobilize the slowly moving charge. Depolarization to -20 mV immobilizes both charge movements, and uncovers the presence of a third charge which seems to correspond to Charge 2 (cf. Adrian & Almers, 1976b; Adrian, Chandler & Rakowski, 1976).