Specificity of inositol trisphosphate-induced calcium release from permeabilized Swiss-mouse 3T3 cells

Swiss-mouse 3T3 cells permeabilized with saponin were used to study the specificity of the inositol trisphosphate-induced release of 45Ca2+ from their intracellular stores. Inositol 1,4,5-trisphosphate was the most potent compound studied (dose giving half-maximal effect 0.3 microM). 45Ca2+ was also released by inositol 2,4,5-trisphosphate, glycerophosphoinositol 4,5-bisphosphate and inositol 4,5-bisphosphate, with doses giving half-maximal effect of respectively 1.6 microM, 1.6 microM and 20 microM, but not by inositol 1,4-bisphosphate (50 microM). These data suggest that the trans-vicinal phosphates on the 4- and 5-positions are essential for the Ca2+-mobilizing effect of inositol trisphosphate, and that in addition there is a requirement for a phosphate group on the opposite side of the molecule, with a preference for the 1-position.