Alteration of calcium sensitivity of skinned frog skeletal muscle fibres by inositol triphosphate and calmodulin antagonists.

We investigated the influence of inositol triphosphate (IP3), trifluoperazine (TFP), and perhexiline on the calcium sensitivity of freeze-dried frog semitendinosus muscle fibres. Further, the effect of IP3 on calcium release from the sarcoplasmic reticulum (SR) of frog semitendinosus fibres skinned by saponin was studied. IP3 decreased the calcium sensitivity of freeze-dried frog skeletal muscle fibres and failed to induce a calcium release from SR of saponin-skinned fibres. Freeze-dried frog skeletal muscle fibres were strongly sensitized for calcium by TFP and perhexiline.