| Abstract: | The membrane properties of individual skeletal muscle cells were studied with intracellular microelectrodes as the fibers developed, in vitro, from mononucleated precursor cells. Passive membrane constants were determined from analysis of transmembrane potential responses to pulses of current assuming the myotubes could be represented as sealed, finite cylinders. Resting membrane potentials increased from 10–15 mV in the shortest, youngest myotubes to ca. 60 mV in the longest, most mature fibers. The increase in membrane potential was not associated with a change in membrane resistivity. Action potentials occurred spontaneously in the most mature cells and repetitive spikes could be evoked by depolarizing current pulses. Spikes and twitches could be evoked in young myotubes provided the membrane was first hyperpolarized to 60–70 mV. Apparently the membrane potential is the rate limiting factor in the maturation of excitation-contraction mechanisms. |
