Contraction of detergent-treated smooth muscle.

After exposure of segments of rabbit taenia coli to the nonionic detergent Triton X-100, tension could be induced by increasing the [Ca2+] in the micromolar range. In the presence of a saturating [Ca2+], this preparation developed nearly 100% of the control tetanus tension recorded from the intact muscle prior to the detergent treatment. In addition, tension could be induced by increasing the [Mg2+], in the virtual absence of Ca2+. Mg2+ seems to inhibit the Ca2+-induced tension in a predominantly competitive manner.