For tension, the colon is then drawn over a 1.5-mm diameter fire-polished capillary tube, whose length exceeds that of the colon. An artificial pellet is mounted to the capillary glass and the colon is positioned with the pellet in the middle. The capillary glass is then fixed to the bottom of the organ bath by the ends protruding from each colonic opening. Suture silk is used to connect three force transducers (model TST125C; Biopac Systems, Santa Barbara, CA) to the proximal, transverse and distal segments of the colon. Resting tension is initially set at 8 mN and monitored using an MP100 interface and recorded on a PC running Acqknowledge software 3.2.6 (Biopac Systems). Two platinum wire electodes are placed on top of proximal or distal colon. Square wave electrical stimulation, pulsewidth 0.3 ms, is applied at various frequencies and durations.