Intramembrane charge movement in developing skeletal muscle cells from fetal mice

The development of intramembrane charge movement was studied in freshly isolated skeletal muscle cells from 13- to 19-day-old mouse fetuses. Charge movement was present in myotubes from 13-day-old fetuses. The relationship between charge movement and membrane potential could be described by a two-state Boltzmann equation. The amount of maximum charge movement (Q_max) increased substantially with the age of the fetuses from 2.84±0.39 nC/F (n=10) at day 13 to 10.01±0.97 nC/F (n=15) at day 19. Nifedipine (1 M) consistently reduced Q_max by 33±2% (n=37) of the control value at each age studied. Increasing the concentration of nifedipine to 20 M had no further effect, suggesting that the charge movement in developing myotubes consists of at least two components: a nifedipine-sensitive charge movement (Q_ns) and a nifedipine-resistant one (Q_nr). Both Q_ns and Q_nr increased exponentially with a distinct enhancement of rate at day 16.