Increased sodium pump activity following repetitive stimulation of rat soleus muscles.

1. Soleus muscles of anaesthetized rats were stimulated tetanically (4 s at 20 Hz every 5 s for 5 min), following which the resting and action potentials were measured in surface fibres. 2. At the end of the stimulation period, the mean resting potential was found to have increased from a control value of -79.5 +/- 4.8 mV (mean +/- S.D.) to -90.5 +/- 6.3 mV. The hyperpolarization started to decline after 9 min but was still present at 15 min. …