title: Calcium-dependent turnover of brain polyphosphoinositides in vitro after prelabelling in vivo.
abstract: Rat brain phospholipids were labelled in vivo by an intraventricular injection of 32P. The radioactivity was found to accumulate predominantly in limbic structures, particularly hippocampus and diencephalon. A rapid and high specific labelling of the inositol phospholipids and phosphatidic acid was observed. The rate of incorporation into a crude myelin fraction was similar to that into a mitochondrial/synaptosomal fraction although phosphatidyl-myo-inositol 4,5-diphosphate was especially enriched in myelin. Upon incubation in vitro  high specific labelling of the inositol phospholipids and phosphatidic acid was observed. The rate of incorporation into a crude myelin fraction was similar to that into a mitochondrial/synaptosomal fraction although phosphatidyl-myo-inositol 4,5-diphosphate was especially enriched in myelin. Upon incubation in vitro  high specific labelling of the inositol phospholipids and phosphatidic acid was observed. The rate of incorporation into a crude myelin fraction was similar to that into a mitochondrial/synaptosomal fraction although phosphatidyl-myo-inositol 4,5-diphosphate was especially enriched in myelin. Upon incubation in vitro of the brain fraction after 2 h prelabelling in vivo, both phosphatidyl-myo-inositol 4-phosphate and phosphatidyl-myo-inositol 4,5-diphosphate rapidly lost their radioactivity. Half of the labile fraction of the incorporated 32P was removed within 2 min. None of the other phospholipids changed in the 30 min in vitro incubation period. The metabolism of the polyphosphoinositide proceeded at a lower rate when the temperature was lowered, and was Ca2+-dependent. Further subcellular fractionation revealed that purified synaptosomes and myelin contained highly labelled phosphatidyl-myo-inositol 4-phosphate or phosphatidyl-myo-inositol 4,5-diphosphate. Mitochondria contained highly labelled phosphatidyl-myo-inositol but no phosphatidyl-myo-inositol 4-phosphate or phosphatidyl-myo-inositol 4,5-diphosphate. ACTH1-24 did not inhibit the in vitro dephosphorylation of prelabelled polyphosphoinositide, confirming previous findings that the peptide affects the polyphosphoinositide kinases and not the respective phosphatases.
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D003366:Cosyntropin / Q000494:pharmacology; D066298:In Vitro Techniques; D007276:Injections, Intraventricular; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D009186:Myelin Sheath / Q000378:metabolism; D010710:Phosphates / Q000008:administration & dosage; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism; D011108:Polymers / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism
chemical_list: D010710:Phosphates; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D011108:Polymers; D003366:Cosyntropin; D002118:Calcium