Figure 1.

Representative traces illustrating muscle relaxations and contractions to EFS in circular muscle from human isolated colon. (A) Trace showing effects of different frequencies of EFS (1, 2, 5, 10, 15 and 20 Hz, 50 V, 0.5 ms bipolar pulse duration) applied for 10 s every 1 min. The horizontal bar indicates the period of EFS, with the response generated during this time usually followed by an ‘after-contraction’ on termination of EFS. Contractions and relaxations during 5 Hz EFS were prevented, respectively, by (B) 1 μM atropine and (C) by 300 μM L-NAME. The enlarged sections of tracing show the ability of atropine to prevent contractions during EFS (revealing muscle relaxation) and greatly reduce the large after-contractions, which followed termination of EFS. Similarly, muscle relaxation was prevented by L-NAME and the resultant contraction became monophasic.