The modulation of force in isolated rat EGTA-treated anococcygeus muscle by phosphate, cyclic AMP and noradrenaline.

Saponin treatment is commonly used to permeabilize the surface membrane of muscle cells. Incubation of isolated rat anococcygeus for 4 h in a low Ca2+ and low Mg2+ solution resulted in the muscle responding to Ca2+, phosphate and cyclic AMP in a similar way to a saponin-treated muscle. However, unlike saponin-treated preparations, the maximal calcium-activated force was stable for many hours and the addition of noradrenaline caused contracture. These properties would permit this preparation to be used to study aspects of receptor-mediated excitation-contraction coupling.