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Changes in the levels of inositol phosphates after agonist-dependent hydrolysis of membrane phosphoinositides.

ABSTRACT: The formation of inositol phosphates in response to agonists was studied in brain slices, parotid gland fragments and in the insect salivary gland. The tissues were first incubated with [3H]inositol, which was incorporated into the phosphoinositides. All the tissues were found to contain glycerophosphoinositol, inositol 1-phosphate, inositol 1,4-bisphosphate and inositol 1,4,5-trisphosphate, which were identified by using anion-exchange and high-resolution anion-exchange chromatography, high-voltage paper ionophoresis and paper chromatography. There was no evidence for the existence of inositol 1:2-cyclic phosphate. A simple anion-exchange chromatographic method was developed for separating these inositol phosphates for quantitative analysis. Stimulation caused no change in the levels of glycerophosphoinositol in any of the tissues. The most prominent change concerned inositol 1,4-bisphosphate, which increased enormously in the insect salivary gland and parotid gland after stimulation with 5-hydroxytryptamine and carbachol respectively. Carbachol also induced a large increase in the level of inositol 1,4,5-trisphosphate in the parotid. Stimulation of brain slices with carbachol induced modest increase in the bis- and tris-phosphate. In all the tissues studied, there was a significant agonist-dependent increase in the level of inositol 1-phosphate. The latter may be derived from inositol 1,4-bisphosphate, because homogenates of the insect salivary gland contain a bisphosphatase in addition to a trisphosphatase. These results suggest that the earliest event in the stimulus-response pathway is the hydrolysis of polyphosphoinositides by a phosphodiesterase to yield inositol 1,4,5-trisphosphate and inositol 1,4-bisphosphate, which are subsequently hydrolysed to inositol 1-phosphate and inositol. The absence of inositol 1:2-cyclic phosphate could indicate that, at very short times after stimulation, phosphatidylinositol is not catabolized by its specific phosphodiesterase, or that any cyclic derivative liberated is rapidly hydrolysed by inositol 1:2-cyclic phosphate 2-phosphohydrolase.

SUBMITTER: Berridge MJ

PROVIDER: S-EPMC1152070 | biostudies-other | 1983 May

REPOSITORIES: biostudies-other

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Project description:Phytate forms insoluble precipitates with various cations that are recalcitrant to digestion in poultry. Dietary supplementation with exogenous phytase has been shown to improve phytate solubility and digestibility and, in turn, improve animal growth performance. Although the kinetics of phytate hydrolysis by exogenous phytase are well described in vitro, the progression of the reaction in vivo is still not well defined. The aim of the present study was, therefore, to monitor the kinetic variation of myo-inositol (myo-Ins) levels in both circulation and feather following exogenous phytase supplementation. In experiment 1, 4 week-old male broilers were individually housed with ad libitum access to water and a standard commercial diet. Birds were maintained under environmental temperature of 24°C and 30% RH. Birds were cannulated in the cutaneous ulnar vein on the right wing and remained untouched for 3 days. On the day of the experiment, birds were randomly divided into three body weight-matched groups and fed either the control diet, the control diet-supplemented with myo-Ins or Ronozyme HiPhos (0.06%, DSM Nutritional Products, Switzerland) for 10 h. In the experiment 2, birds were fed only HiPhos for 30 h. Growing feathers and blood were collected at baseline and then every 2 h for 10 h (experiment 1) and 30 h (experiment 2) post-prandially. Plasma and feather myo-Ins levels were determined by UHPLC-MS/MS. The relative expression of inositol polyphosphate-1-phosphatase (INPP1), inositol hexakisphosphate kinase 1-3 (IP6K1-3), inositol-3-phosphate synthase (ISYNA), and multiple inositol-polyphosphate phosphatase 1 (MNPP1) genes in blood and feathers was determined by real-time qPCR using 2-ΔΔCt method. Plasma and feather myo-Ins levels were significantly increased by HiPhos at 6 h to 8 h post-prandial. The mRNA abundances of INPP1, IP6K1, and ISYNA in the circulation were significantly down regulated at all periods compared to the baseline levels. IP6K2, IP6K3, and MINPP1 gene expression, however, was up regulated at 8 h post-prandial and then returned to the baseline levels. In feathers, the expression of INPP1 was induced at 8 h post-prandial and remained higher compared to the baseline. The expression of IP6K2, IP6K3, and MINPP1 was down regulated during the first 10 h and then returned to baseline levels for the rest of the post-prandial period. Taken together, our data show that phytase modulates the expression of genes associated with myo-Ins metabolism and generates release of myo-Ins in both circulation and feather at 6-10 h post-feeding. Feather myo-Ins concentration could be used as a non-invasive method to monitor phytate hydrolysis in practice.

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Changes in the levels of inositol phosphates after agonist-dependent hydrolysis of membrane phosphoinositides.

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