Specificity of inositol phosphate-stimulated Ca2+ mobilization from Swiss-mouse 3T3 cells

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Abstract
Pure samples of inositol 1,3,4-trisphosphate, inositol 1,3,4,5-tetrakisphosphate and inositol 1,2-cyclic 4,5-trisphosphate were prepared and tested for their ability to mobilize calcium from intracellular stores in a permeabilized Swiss mouse 3T3 cell preparation. In this system inositol 1,4,5-trisphosphate mobilizes Ca2+ with a half-maximal dose of 0.3 .mu.M. Inositol 1,2-cyclic 4,5-trisphosphate mobilized Ca2+ to the same extent with a half-maximal dose of 0.3 .mu.M, whereas inositol 1,3,4-trisphosphate required a half-maximal dose of approx. 9 .mu.M to give the same effect. Inositol 1,3,4,5-tetrakisphosphate was ineffective up to 20 .mu.M and at that concentration did not antagonize the mobilization induced by inositol 1,4,5-trisphosphate. The relevance of these findings to the function of the inositol tris/tetrakis-phosphate pathway is discussed.