| Abstrakt: |
When myo-[3H]inositol-prelabelled primary-cultured murine bone-marrow-derived macrophages were challenged with platelet-activating factor (PAF; 200 ng/ml), there was a rapid (2.5-fold at 10 s) rise in the intracellular concentration of D-myo-[3H]inositol 1,4,5-trisphosphate, followed by a rise in myo-[3H]inositol tetrakisphosphate. myo-[3H]Inositol tetrakisphosphate fractions were isolated by high-performance anion-exchange chromatography from myo-[3H]inositol-prelabelled chick erythrocytes and primary-cultured macrophages. In both cases [3H]iditol and [3H]inositol were the only significant products (greater than 90% of recovered radioactivity) after oxidation to completion with periodic acid, reduction with NaBH4 and dephosphorylation with alkaline phosphatase. The presence of [3H]inositol after this procedure is consistent with the occurrence of [3H]inositol 1,3,4,5-tetrakisphosphate in the cell extracts, whereas [3H]iditol could only be derived from D- or L-inositol 1,4,5,6-tetrakisphosphate. When [3H]inositol tetrakisphosphate fractions obtained from (A) unstimulated macrophages, (B) macrophages that had been stimulated with PAF for 40s or (C) chick erythrocytes were subjected to the above procedure, radioactivity was recovered in these polyols in the following proportions: A, 60-90% in iditol, with 10-40% in inositol; B, total radioactivity increased by a factor of 9.8, 94% being recovered in inositol and 8% in iditol; C, 70-80% in iditol and 20-30% in inositol. [3H]Iditol derived from myo-[3H]inositol tetrakisphosphate fractions from macrophages and chick erythrocytes was oxidized to sorbose by L-iditol dehydrogenase (L-iditol:NAD+2-oxidoreductase, 1.1.1.14) at the same rate as authentic L-iditol. D-[14C]Iditol, derived from D-myo-inositol 1,4,5-trisphosphate, was not oxidized by L-iditol dehydrogenase. This result indicates that the [3H]iditol was derived from L-myo-inositol inositol 1,4,5,6-tetrakisphosphate. The data are consistent with rapid PAF-sensitive synthesis of D-myo-[3H]inositol 1,3,4,5-tetrakisphosphate in macrophages, and demonstrate that L-myo-inositol 1,4,5,6-tetrakisphosphate is synthesized in both mammalian and avian cells. The levels of L-myo-[3H]inositol 1,4,5,6-tetrakisphosphate in primary-cultured macrophages are not acutely sensitive to PAF. |
