Smooth Muscle Contractility Measurements

Contractions of smooth muscle strips were recorded in human ileum and sigmoid colon in situ, according to a previous method [33 (link)] with minor modifications. After removing the mucosal and submucosal layer of ileum and sigmoid colon, muscle layer was cut into strips of 5–6 mm in length and 2–3 mm in width. The muscle strips were mounted to an isometric force transducer (Biopac Systems, Inc., Goleta, CA, USA) and suspended in 10 mL organ bath containing aerated (97% O₂ and 3% CO₂) and warmed (36.5 ± 0.5 °C) KRB solution. The muscle strips were stabilized for 60 min without a force and equilibrated for 60 min after stretching the strips to 1 mN, in the presence of L-NNA (100 μM) and MRS 2500 (1 μM) to eliminate inhibitory responses. Electrical field stimulation (EFS; 10 Hz, 10 s, 100 V, 0.3 ms pulse) was applied to evoke neural response using a Grass S88 stimulator (Grass instruments, Warwick, RI, USA).