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  • Title: Endogenous phosphoinositide precursors of inositol phosphates in rat brain cortical membranes.
    Author: Claro E, Sarri E, Picatoste F.
    Journal: Biochem Biophys Res Commun; 1993 Jun 30; 193(3):1061-7. PubMed ID: 8391798.
    Abstract:
    The appearance of Ins1P as an index of direct PtdIns breakdown by phospholipase C was examined in rat brain cortical membranes using either exogenous [3H]PtdIns substrate or [3H]inositol-prelabeled endogenous phosphoinositide substrates. Production of [3H]Ins1P was observed using exogenous [3H]PtdIns but not with endogenous substrate over the physiological range of calcium concentrations. [3H]Ins1,4P2 and [3H]Ins4P, derived from phospholipase C breakdown of polyphosphoinositides, were formed by membranes from both exogenous [3H]PtdIns and endogenous 3H-phosphoinositides, in the presence of ATP. The contribution of endogenous PtdInsP2 and PtdInsP to the generation of inositol phosphates was examined in membranes from [3H]inositol-prelabeled brain slices by adding unlabeled Ins1,4,5P3 to trap [3H]Ins1,4,5P3 generated upon breakdown of [3H]PtdInsP2. The maximal rate of [3H]Ins1,4,5P3 appearance was attained in the presence of 150-200 microM added Ins1,4,5P3 and represented 12.5% of the combined rates of formation of [3H]Ins1,4,5P3 and [3H]Ins1,4P2, similar to the content of [3H]PtdInsP2 relative to total 3H-polyphosphoinositides. The results show that, while endogenous PtdIns is not degraded by phospholipase C, the enzyme appears to be equally effective to cleave endogenous PtdInsP2 and PtdInsP.
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