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  • Title: Calcium-dependent turnover of brain polyphosphoinositides in vitro after prelabelling in vivo.
    Author: Jolles J, Schrama LH, Gispen WH.
    Journal: Biochim Biophys Acta; 1981 Oct 23; 666(1):90-8. PubMed ID: 6271236.
    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.
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