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 (Qmax) increased substantially with the age of the fetuses from 2.84 +/- 0.39 nC/microF (n = 10) at day 13 to 10.01 +/- 0.97 nC/microF (n = 15) at day 19. Nifedipine (1 microM) consistently reduced Qmax by 33 +/- 2% (n = 37) of the control value at each age studied. Increasing the concentration of nifedipine to 20 microM had no further effect, suggesting that the charge movement in developing myotubes consists of at least two components: a nifedipine-sensitive charge movement (Qns) and a nifedipine-resistant one (Qnr). Both Qns and Qnr increased exponentially with a distinct enhancement of rate at day 16.