An in vitro method for the study of beta-receptor mediated effects on slow contracting skeletal muscle

The soleus muscle of a guinea-pig was dissected out under pentobarbitone anaesthesia and mounted on a holder in an organ bath containing Krebs solution. The tendon was attached to a force transducer and subtetanic contractions were evoked by electrical field stimulation (0.5 ms pulses at 10-12 Hz for 1.5 or 3 s every 22 s). The experiments were performed at 37 degrees. Terbutaline, a selective agonist at beta2-adrenoceptors, reduced the force of subtetanic contractions in a dose-dependent manner, the EC50 being 0.2 muM. The reduction was due to a lessened degree of fusion. The results conform to previous in vivo studies.