Figure 6. Effects of electrical stimulation during incubation in Li⁺-KR buffer on [Na⁺]_i and ⁸⁶Rb⁺ uptake rate in rat soleus muscle.

Muscles mounted isometrically on electrodes were preincubated for 30 min in KR buffer followed by 10 min of preincubation in Li⁺-KR buffer. Then they were stimulated for 10 s at 60 Hz (1 ms pulses at 10 V) and immediately transferred into tubes containing standard KR buffer with ⁸⁶Rb⁺ (0.1 μCi ml⁻¹) and incubated for 1 min. Finally the muscles were washed 4 × 15 min in ice-cold Na⁺-free Tris-sucrose buffer, blotted and taken for counting of ⁸⁶Rb⁺ activity and determination of [Na⁺]_i (see Methods for details). Each column represents the mean value with bars denoting s.e.m. of observations on 5 muscles.