Figure 1. Time course of the effects of salbutamol on [Na⁺]_i and ⁸⁶Rb⁺ uptake rate in rat soleus muscle.

Groups of four muscles in polyethylene baskets were preincubated for 2 × 30 min in KR buffer. At time zero they were transferred into KR buffer containing ⁸⁶Rb⁺ (0.1 μCi ml⁻¹) ± 10⁻⁵m salbutamol and incubated for 1–5 min. After incubation the muscles were washed for 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). •, control muscles; ○, incubated with 10⁻⁵m salbutamol. Each point represents the mean value ± s.e.m. of observations on 4 muscles.