Inositol 1,4,5-trisphosphate-induced Ca2+ release from permeabilized mastocytoma cells

The effect of inositol 1,4,5-trisphosphate (IP3) on Ca2+ release in the transformed murine mast cells, mastocytoma P-815 cells permeabilized with digitonin was studied. Ca2+ was sequestered by intracellular organelles in the presence of ATP until the medium free Ca2+ concentration was lowered to a new steady-state level. The subsequent addition of IP3 caused a rapid Ca2+ release, which was followed by a slow re-uptake of Ca2+. Fifty percent of the sequestered Ca2+ was released by 10 microM IP3. Maximal Ca2+ release occurred at 10 microM and half maximal activity was at 1.3 microM. These results indicate that IP3 may function as a messenger of intracellular Ca2+ mobilization in mastocytoma cells.