Inositol 1,4,5-trisphosphate enhances Ca2+-sensitivity of the contractile mechanism of chemically skinned rabbit skeletal muscle fibres.

The possibility that inositol 1,4,5-trisphosphate may also act on subcellular structures different from membraneous compartments has been examined using chemically skinned skeletal muscle fibres. At about 1 to 25 microM IP3 reversibly enhanced isometric steady-state force production of these preparations at free Ca2+ concentrations corresponding to submaximum activation in a concentration-dependent manner. The maximum Ca2+-induced tension was not altered by IP3. These results show that IP3 can modulate the apparent Ca2+-sensitivity of the contractile mechanism. They suggest a new modulatory function of IP3 in skeletal muscle.