The use of cells doubly labelled with [14C]inositol and [3H]inositol to search for a hormone-sensitive inositol lipid pool with atypically rapid metabolic turnover

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Colleges, School and Institutes

Abstract

Some, though not all, previous studies have suggested that the inositol lipid which is hydrolysed during transmembrane signalling in response to receptor activation might be drawn from a metabolically discrete and relatively small hormone-sensitive lipid pool that turns over more rapidly than the bulk of membrane inositol lipid. In order to seek evidence for the existence of this putative hormone-sensitive lipid pool, we have double-labelled cells by growing them for 3 days in a medium containing [14C]inositol and then supplying them with [3H]inositol for the final 2 h before stimulation. We anticipated that stimulation of these doubly labelled cells might provoke the formation, from the postulated hormone-sensitive pool, of small quantities of relatively3H-enriched inositol phosphates, and that these could be harvested from cells (provided that the cytosolic inositol monophosphatase and inositol 1,4-bisphosphate/inositol 1,3,4-trisphosphate 1-phosphatase activities are first inhibited by Li+). Experiments of this type, using both vasopressin-stimulated WRK1 rat mammary tumour cells and 3T3 mouse fibroblasts stimulated by prostaglandin F(2α), have largely failed to demonstrate the formation of relatively3H-enriched inositol phosphates. There was a tendency for phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bis-phosphate to have slightly higher3H :14C ratios than phosphatidylinositol, but the3H :14C ratios than phosphatidylinositol, but the3H :14C ratios of the inositol phosphates formed in stimulated cells were not substantially greater than the3H :14C ratios of the inositol lipids. We therefore conclude, at least for the two cell lines that we studied, that hormone-stimulated inositol lipid hydrolysis can call, either directly or indirectly, upon the majority of the inositol lipid complement of the stimulated cell.

Details

Original languageEnglish
Pages (from-to)379-389
Number of pages11
JournalJournal of Endocrinology
Volume122
Issue number1
Publication statusPublished - 1 Jan 1989