Calcium-dependent turnover of brain polyphosphoinositides in vitro after prelabelling in vivo

J. Jolles, L.H. Schrama, W.H. Gispen

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    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 phosphatidylmyo-inositol 4, 5-diphosphate was especially enriched in myelin. Upon incubation in vitro of the brain fractions after 2 h prelabelling in vivo, both phosphatidylvnyo-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, 5-diphosphate. Mitochondria contained highly labelled phosphatidyl-myo-inositol but no phosphatidyl-myo-inositol 4-phosphate or phosphatidyl-myo-inositol 4, 5-diphosphate. ACTUH1–24 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.
    Original languageEnglish
    Pages (from-to)90-98
    Number of pages9
    JournalBBA - Lipids and Lipid Metabolism
    Issue number1
    Publication statusPublished - 1 Jan 1981

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