Some electrophysiological properties of developing rat skeletal myotubes grown in serum-free, chemically defined...

Serum-free, chemically defined media have been reported to provide suitable conditions for growth and proliferation of mammalian skeletal muscle, but there is no information regarding the ability of myotubes to develop normal electrophysiological properties in these media. We have recorded transmembrane resting and action potentials from rat skeletal myotubes grown in both serum-containing (GM) and serum-free chemically defined (CDM) growth media. Muscle cells in CDM do not develop as high resting Em as their counterparts in conventional growth media. CDM myotubes also had a lower incidence and frequency of spontaneously occurring action potentials. Treatment with ouabain or decrease in temperature of the recording medium reduced resting Em of both GM and CDM cells to the same level. We found that the sensitivity of CDM cells to ouabain was about 10-fold higher than that of GM cells. An increase in temperature of the recording medium increased Em of GM myotubes but not of CDM myotubes. The change in resting Em in response to a 10-fold change in extracellular K(+)-ion concentration was the same for both groups of cells thus indicating that there was no difference in membrane permeability to K(+)-ion. We conclude that the difference in Em can be accounted for largely, if not entirely, by differences in activity or amount of electrogenic Na(+)-K(+) ATPase.