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PubMed1996

Interferon-gamma increases inositol phosphate formation and cellular calcium ion concentration independent of ICAM-1 antigen enhancement in renal tubular cells.

In the present study, we investigated the effect of interferon-gamma (IFN-gamma) on cellular inositol phosphate formation and cellular calcium ion concentration [Ca2+]i in human renal proximal tubular (HRPT) cells. We also examined the possible role of the inositol phosphate-Ca2+ signalling pathway during IFN-gamma-induced intercellular adhesion molecule-1 (ICAM-1) antigen expression. IFN-gamma caused an increase in the formation of inositol 1-monophosphate (Ins 1-P), inositol 1,4-bisphosphate (Ins 1,4-P2), inositol 1,4,5-trisphosphate (Ins 1,4,5-P3) and inositol 1,3,4,5-tetrakisphosphate (Ins 1,3,4,5-P4). A rapid time-dependent rise in [Ca2+]i was observed upon IFN-gamma stimulation, with maximal levels reached after 1 min. A lower rise in [Ca2+]i was observed when cells were stimulated in Ca2+-free medium. This correlated with the generation of Ins 1,4,5-P3 by IFN-gamma, a well-known secondary messenger capable of releasing Ca2+ from intracellular stores. The induction of ICAM-1 antigen expression was enhanced by IFN-gamma, 4-bromocalcium ionophore A23187 (Bromo-A23187), and their combinations. However, the calcium antagonist diltiazem and calcium chelator EGTA had no effect on IFN-gamma antigen induction. In conclusion, our data suggest that IFN-gamma stimulation of HRPT cells results in the cleavage of phosphatidylinositol bisphosphate by phospholipase C, generating inositol phosphates, of which Ins 1,4,5-P3 probably releases Ca2+ from intracellular stores. A further increase in [Ca2+]i upon IFN-gamma stimulation results from influx of extracellular Ca2+. IFN-gamma signal transduction in HRPT cells may not be limited to the inositol phosphate-Ca2+ pathway since IFN-gamma-induced ICAM-1 antigen expression was unaffected by calcium antagonist/chelator.

Calcimycin↗
PubMed1993

Inositol phosphates and cell signaling: new views of InsP5 and InsP6.

Ins(1,3,4,5,6)P5 and InsP6 comprise the bulk of the inositol phosphate content of mammalian cells, but their intracellular functions are unknown. Until recently it seemed that these compounds were metabolically lethargic; this has diverted attention away from their possible role in short-term regulation of physiological processes. Interest in the idea that these polyphosphates play more dynamic roles is now increasing, following recent demonstrations that they are precursors of several inositol phosphates that turnover rapidly.

Animals↗
PubMed2005

[Alterations of expression of G protein-inositol phosphates pathway-related genes in essential hypertension: experiment with spontaneously hypertensive rats].

OBJECTIVE: To investigate the changes of G protein-inositol phosphates pathway-related genes and evaluate the role of such changes in the pathogenesis of essential hypertension. METHODS: The pressures of the caudal arteries and body weights of 30 spontaneous hypertensive rats (SHRs), 7 two-week-old, 7 4-week-old, 6 six-week-old, 6 eight-week-old, 6 ten-week-old, and 6 twelve-week-old, and 38 normotensive Wistar-Kyoto (WKY) rats, 6 two-week-old, 6 four-week-old, 6 six-week-old, 6 six-week-old, 6 eight-week-old, 7 ten-week-old, and 7 twelve-week-old, were measured. Then the rats were killed and their hearts, aortas, livers, and kidneys were taken out. 294 specimens of total RNA were obtained from the tissues of ventricle of heart, aortic smooth muscle, liver and kidney. RNA array was used to determine the mRNA levels of G proteins G11 and Gq, and phospholipase C-beta (PLCbeta). RESULTS: The systolic blood pressures of the 6, 8, 10, and 12-week-old SHRs were 158 mm Hg +/- 8 mm Hg, 174 mm Hg +/- 4 mm Hg, 198 mm Hg +/- 13 mm Hg, and 217 mm Hg +/- 9 mm Hg respectively, all significantly higher than those of the age-matched WKY rats (109 mm Hg +/- 6 mm Hg, 128 mm Hg +/- 5 mm Hg,142 mm Hg +/- 4 mm Hg, and 141 mm Hg +/- 5 mm Hg respectively, all P <0.01). The cardiosomatic ratios of the 10- and 12-week-old SHRs were both significantly higher than those of the age-matched WKY rats (both P < 0.01). The G11 mRNA levels in the heart tissue of the 4, 6, 8, 10, and 12-week-old SHRs were 1.42 +/- 0.35, 1.87 +/- 0.40, 1.96 +/- 0.24, 2.09 +/- 0.38, and 2.34 +/- 0.45, all significantly higher than those of the age-matched WKY rats (1.05 +/- 0.18, 1.25 +/- 0.37, 1.26 +/- 0.35, 1.45 +/- 0.30, and 1.51 +/- 0.42 respectively, P < 0.05 or P < 0.01). The Gq mRNA levels of the 4, 6, 8, 10, and 12-week-old SHRs were 1.12 +/- 0.21, 1.30 +/- 0.26, 1.45 +/- 0.35, 1.77 +/- 0.42, and 2.05 +/- 0.46, respectively, all significantly higher than those of the age-matched WKY rats (0.88 +/- 0.09, 0.96 +/- 0.10, 1.03 +/- 0.10, 1.21 +/- 0.38, and 1.29 +/- 0.39 respectively, P < 0.05 or P < 0.01). Similar results were found in the G11 and Gq mRNA levels of the aorta and kidney tissues. The levels of PLCbeta expression in the heart and kidney tissues of the 4, 6, 6, 8, 10, and 12-week-old SHRs were all significantly increased (P <0.05 or P <0.01). Galpha, Gq, and PLCbeta were not significantly expressed in the liver. PLCbeta was hardly found in the aorta. CONCLUSION: Increase of the expression of G protein-inositol phosphates pathway-related genes is an important molecular biological mechanism in the pathogenesis and development of essential hypertension.

Algorithms↗
PubMed1989

Short-term desensitization of prostaglandin F2 alpha receptors increases cyclic AMP formation and reduces inositol phosphates accumulation and contraction in the bovine iris sphincter.

The effect of short-term prostaglandin (PG) desensitization on PGF2 alpha receptor-mediated inositol phosphates accumulation, 1,2-diacylglycerol production, measured as phosphatidic acid (PA), myosin light chain (MLC) phosphorylation, cAMP formation and contraction was investigated in bovine iris sphincter smooth muscle. We have found that incubation of the sphincter with 25 microM PGF2 alpha for 45 min leads to: (a) significant loss in sensitivity of the tissue to PGF2 alpha receptor-stimulated inositol phosphates accumulation, PA production, MLC phosphorylation and contraction, and (b) significant increase in both basal and PGF2 alpha-stimulated cAMP formation. These changes are probably not due to reduction in phospholipid synthesis because there were no detectable differences in basal phospholipid labeling, either from 3H-inositol or from 32P, between normal and desensitized muscles. Preincubation of the sphincter in the absence of PGF2 alpha for 45 min did not lead to alterations in the biochemical-pharmacological responsiveness of the control muscle to PGF2 alpha. Our results suggest that desensitization of PG receptors in the iris sphincter occurs by a receptor-specific process. The PG receptor mediating contraction (IP3-Ca2+) is selectively susceptible to desensitization, in contrast with the receptor mediating smooth muscle relaxation (cAMP). These findings add further support to the developing hypothesis that there are functional and biochemical reciprocal interactions between the IP3-Ca2+ and cAMP messenger systems in the iris of the mammalian eye.

Animals↗
PubMed1990

Kallidin-induced stimulation of inositol phosphate production and prolactin release in rat anterior pituitary cells.

The effect of the kinin, kallidin (lysyl-bradykinin) on phosphoinositide metabolism and prolactin secretion was examined in male rat anterior pituitary cells in primary culture. Kallidin was found to stimulate both total inositol phosphate production and prolactin release. The stimulation of inositol phosphate was biphasic in nature, similar to that previously reported for bradykinin, although kallidin was approximately 10-fold more potent. Kallidin also stimulated prolactin secretion provoking a maximal stimulation of 193.0 +/- 11.1 (sem)% at 1 mumol/l. These findings suggest that kallidin-induced prolactin secretion may be mediated intracellularly by activation of phosphoinositide metabolism. The B2 receptor antagonists had no significant inhibitory effects on kallidin-stimulated phosphoinositide metabolism or prolactin release. The B1 agonist des-Arg9-bradykinin has previously been shown to have no effect on either parameter. As the effects of kinins on anterior pituitary cells do not appear to be mediated by either of the known kinin receptors, they may, therefore, act via a hitherto unrecognised kinin receptor.

Animals↗
PubMed1988

Lowering of the extracellular Na+ concentration enhances high-K+-induced formation of inositol phosphates in the guinea-pig ileum.

1. Formation of inositol phosphates (InsPs) was measured in cross-chopped slices or dispersed cells, isolated by collagenase treatment, of guinea-pig ileum longitudinal smooth muscle pre-labelled with [3H]inositol. 2. Elevation of the extracellular K+ concentration by equimolar replacement of Na+ induced accumulation of InsPs in the dispersed cells and in the tissue slices. These effects were blocked by neither tetrodotoxin (1 microM) nor atropine (10 microM), and were approximately additive with carbachol-induced accumulation. 3. In the tissue slices, the response to K+ was partially inhibited by nifedipine (10 microM) and by CdCl2 (0.3 mM), but the carbachol-induced response was not altered. 4. Accumulation of InsPs induced by KCl-excess solution (high-K+ solution without Na+ replacement) was suppressed strongly by nifedipine and completely by CdCl2. The response to KCl excess was approx. 40% of that to high K+ with Na+ replacement. 5. Low-NaCl solution (replacement of NaCl with equimolar sucrose) also produced InsPs, and this was not blocked by either nifedipine (10 microM) or CdCl2 (0.3 mM). 6. The formation of InsPs by a maximally effective concentration of carbachol (1 mM) in the presence of KCl excess or low NaCl was greater than the additive effect of the two stimuli on their own. Enhancement of the carbachol-induced response by KCl excess disappeared in the presence of CdCl2 (0.3 mM). 7. These data suggest that formation of InsPs induced by high-K+ solution with equimolar replacement of Na+ consists of two components, i.e. high-K+-induced inositol-phospholipid hydrolysis by Ca2+ entry through voltage-sensitive channels, and low-Na+-induced formation of InsPs, insensitive to Ca2+ antagonists, but that both of them do not contribute significantly to the activation of phospholipase C by muscarinic stimuli.

Animals↗
PubMed1989

Changes in extracellular calcium within the physiological range influence receptor-mediated inositol phosphate responses in brain and tracheal smooth muscle slices.

The effect of changes in extracellular calcium concentration ([Ca2+]e) on the incorporation of myo-[2-3H]-inositol into phosphoinositides and agonist-stimulated 3H-inositol phosphates (3H-InsPs) was examined in rat cerebral cortex and bovine tracheal smooth muscle slices. In brain slices, reduction in [Ca2+]e from 2.4 to 1.2 mmol/l resulted in an approximate doubling of the carbachol and noradrenaline-stimulated 3H-InsP response with no effect on the EC50 values. An identical effect of varying [Ca2+]e was observed for carbachol-stimulated 3H-InsP formation in tracheal smooth muscle with a further increase in 3H-InsPs evident at [Ca2+]e 0.6 mmol/l. In this tissue the effect of changes in [Ca2+]e on the incorporation of myo-[2-3H]-inositol into the total phosphoinositide pool directly paralleled the changes in 3H-InsPs except in conditions of no added calcium when 3H-InsP responses were markedly impaired. Additional studies in brain slices using buffer where the added calcium varied between 0 and 2.4 mmol/l, showed that both the carbachol stimulated formation of separate inositol phosphates during short incubation periods and incorporation of myo-[2-3H]-inositol into PtdInsP and PtdInsP2 under basal conditions was maximal at [Ca2+]e 0.3 mmol/l. Omitting Ca2+ from the buffer resulted in maximal labelling of PtdIns but a decrease in PtdInsP and PtdInsP2 labelling (compared with the level at [Ca2+]e 0.3 mmol/l) and a markedly impaired inositol polyphosphate response. Alterations in [Ca2+]e following 3H-inositol labelling but immediately prior to carbachol stimulation did not influence 3H-inositol polyphosphate responses. It is therefore clear that even relatively small changes in [Ca2+]e markedly influence agonist-stimulated 3H-InsP responses in brain and tracheal smooth muscle slices and that these reflect changes in the labelling of substrate inositol lipids.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Facilitated calcium mobilization and inositol phosphate production in the priming effect of LH-releasing hormone in the rat.

The ability of LHRH to induce Ca2+ mobilization and production of inositol phosphates in rat anterior pituitary tissue in vitro was investigated in relation to the self-priming effect of LHRH. Prior exposure to LHRH (which caused a characteristic potentiation of subsequent secretory responses) specifically enhanced LHRH-induced inositol phosphate production and mobilization of intracellular Ca2+ stores. LHRH-induced influx of Ca2+ through dihydropyridine-sensitive Ca2+ channels was unaltered, as was ligand binding to LHRH receptors. These data suggest that a novel facilitation of signalling may occur in the phospho-inositide-Ca2+ mobilization response mechanism during LHRH priming, and that this may represent an important means of regulating cellular responsiveness in gonadotrophs.

Animals↗
PubMed2002

Cellular signalling in Trypanosoma cruzi: biphasic behaviour of inositol phosphate cycle components evoked by carbachol.

Stimulation of epimastigote forms of Trypanosma cruzi with carbachol resulted in a long-lasting response. The earlier phase for inositol phosphates was rapid and transient, peaking at 1 min with a return to basal levels by 6 min. In a second phase, these metabolite levels reached maximal values at 10-12 min, with a later declination to basal values at about 20 min. The inositol phosphate response was quenched by parasite treatment with atropine. The elevation in intracellular free calcium ([Ca(2+)]i) was transient, reaching the resting level at 87+/-8 s (n=48) of agonist addition. Myo-inositol 1,4,5-triphosphate (InsP(3)) production and [Ca(2+)]i mobilisation were carbachol dose-dependent. The maximally effective concentrations of agonist ranged between 1x10(-6) and 1x10(-5) M. The increase in carbachol concentration resulted in an evident attenuation of [Ca(2+)]i mobilisation and in [3H]InsP(3) levels. Pretreatment of the cells with 10 microM U73122, a phospholipase C (PLC) inhibitor, showed that both InsP(3) peaks triggered by carbachol were completely abolished, whereas there was not substantial change on the maximum elevation in [Ca(2+)]i. The first peak of InsP(3) and InsP(s) was completely abolished when the cells were incubated with phorbol 12-myristate 13-acetate ester (TPA) for 30 min before carbachol stimulation. A biphasic behaviour for PtdIns 4-kinase activity was demonstrated by changes in [32P]PtdInsP levels. The time-course of PtdIns4P 5-kinase activity showed a rapid, significant and transient decrease of [32P]PtdInsP(2) from 0 time to the third min. At the end of this time the polyphosphoinositide began to return towards control levels but, interestingly, after 5-6 min of stimulation there was a subsequent more important increase over control levels which peaked at 10 min. There was also a detectable increment of DAG at 1 min with a maximum at 3 min, this level remaining elevated until at least 10 min. Subsequently, these levels returned to the base line or even below it.

1-Phosphatidylinositol 4-Kinase↗
PubMed1991

Inositol phosphate formation in uterine tissue from two species of reptiles is stimulated by arginine vasotocin and influenced by stage of reproduction.

Phosphoinositide hydrolysis, resulting in inositol trisphosphate (IP3) and diacylglycerol (DG) formation, has been implicated in oxytocin-stimulated pulsatile secretion of prostaglandin F2 alpha (PGF2 alpha) from uterine endometrium of sheep and other mammals. In reptiles, arginine vasotocin (AVT) stimulates uterine secretion of PGF2 alpha. These studies investigated the ability of AVT to stimulate incorporation of [3H]inositol into inositol mono-, bis-, and trisphosphates in two reptilian species. In Experiment 1, AVT stimulated (P less than 0.01) IP formation in uterine from late-gravid (150 to 291%) and postpartum (104 to 363%) Yarrow's spiny lizards (Sceloporus jarrovi). Inositol phosphate formation, in response to AVT, was greater (P less than 0.01 for IP3 and P less than 0.05 for total IP) for gravid (stage 40 embryos) and postpartum (1-2 days) lizards near the time of parturition than for lizards at other stages (stage 38-39 embryos or 7 days postpartum). Inositol phosphate formation was greater (P less than 0.05) in uterine tissue from gravid than from postpartum lizards. In Experiment 2, basal IP formation and the response to AVT were the greatest (P less than 0.01) in endometrium from late-gravid American alligators (Alligator mississippiensis). AVT stimulated (P less than 0.02) IP synthesis in uterine endometrium from vitellogenic (136 to 394%), early-gravid (7 to 270%), late-gravid (315 to 1002%), postpartum (86 to 313%), and nonreproductive (292 to 322%) alligators. Results indicate that (1) AVT stimulates IP formation in the uterus of reptiles; (2) uterine IP formation increases in late-gravid reptiles; and (3) increased responsiveness to AVT may occur at parturition or oviposition.

Animals↗
PubMed1993

GRP-preferring bombesin receptors increase generation of inositol phosphates and tension in rat myometrium.

In the estrogen-treated rat myometrium, bombesin (Bn) and related agonists triggered contraction and the increased generation of inositol phosphates. The relative order of potencies was identical for both responses: Bn = gastrin releasing peptide (GRP) = litorin = neuromedin C >> neuromedin B. Two specific GRP-preferring receptor antagonists, namely [D-Phe6]Bn-(6-13) methyl ester and [Leu14,psi 13-14]Bn were inhibitory for both Bn-mediated tension and generation of inositol phosphates. [125I-Tyr4]Bn bound to myometrial membranes with high affinity (Kd = 104 pM) to a single class of sites in a saturable and reversible manner. The relative potencies for inhibiting binding were GRP = litorin = [Tyr4]Bn (Ki = 0.4 to 0.6 nM) >> neuromedin B (Ki = 10.3 nM). The high affinity displayed by [D-Phe6]Bn-(6-13) methyl ester (Ki = 2.8 nM) and [Leu14,psi 13-14]Bn (Ki = 35 nM) for competing for [Tyr4]Bn binding supported the involvement of a GRP-preferring Bn receptor. Guanine nucleotides decreased the binding of [125I-Tyr4]Bn and accelerated the rate of ligand dissociation, reflecting the coupling of receptors to guanine nucleotide regulatory proteins (G proteins). The results demonstrate that rat myometrium expresses functional GRP-preferring Bn receptors whose activation stimulates the phospholipase C pathway, pertussis toxin-insensitive event that contributes to Bn-mediated uterine contractions.

Adenosine Triphosphate↗
PubMed1995

Effects of some novel D-myo-inositol-phosphate derivatives on binding and sympathetic transmission.

The vascular effects of myo-inositol and a series of D-myo-inositol phosphate derivatives: D-myo inositol-1-monophosphate (Ins[1]P1), D-myo-inositol-2-monophosphate (Ins[2]P1), D-myo-inositol-1, 2-biphosphate (Ins[1,2,6]P2), D-myo-inositol-1,2,6-trisphosphate (Ins[1,2,6]P3, alpha-trinositol; PP56), D-myo-inositol-1,2,5,6-tetraphosphate (Ins[1,2,5,6]P4), and D-myo-inositol-1,2,3,4,5,6-hexa-phosphate (InsP6, phytic acid) were studied in binding assays in rat heart membranes, in vitro in isolated guinea pig basilar artery, and in vivo in pithed rats. In binding assays in rat heart membranes, Ins[1,2,6]P3, Ins[1,2,5,6]P4, and InsP6 displaced the binding of [3H] alpha-trinositol [3H]Ins[1,2,6]P3). In the isolated guinea pig basilar artery, Ins[1,2]P2 and Ins[1,2,6]P3 inhibited the contractile effects of exogenous neuropeptide Y (NPY) in the concentration range of 10(-8)-10(-6) M. In pithed Sprague-Dawley rats, Ins[1,2,6]P3 inhibited the NPY-induced pressor response in the dose range [2 mg/kg (3.8 mumol/kg) combined with an infusion of 20 mg/kg/h (38 mumol/kg/h) for 30 min] in which no inhibitory effects on the pressor responses were elicited by preganglionic nerve stimulation (PNS) or a bolus injection of phenylephrine (Phe). Ins[1,2]P2 had only slight NPY inhibitory effects in vivo. We conclude that selected inositol derivatives may inhibit the vasopressor effects to NPY in vitro and in vivo. In particular, Ins[1,2,6]P3, which most readily inhibited the NPY-induced pressor response in vivo, may represent a new class of synthetic nonpeptide drugs, which may inhibit the vascular effects of NPY without binding to the NPY receptor itself.

Analysis of Variance↗
PubMed2005

Inositol phosphate profiling of fermented cowpeas by 1H NMR spectroscopy.

The inositol phosphate content of naturally fermented cowpeas (Vigna sinensis var. Carilla) was studied using ion-pair HPLC and 1H NMR spectroscopy. The fermented flour was extracted with 0.5 M HCl, and the extract was purified and fractionated by ion-exchange chromatography. 1H NMR allowed for the identification of two monophosphates [Ins(1 or 3)P1 and Ins(4 or 6)P1], one inositol diphosphate [Ins(1,4)P2], three inositol triphosphates [Ins(1,2,6)P3, Ins(1,5,6)P3, and Ins(1,4,5)P3], one inositol tetraphosphate [Ins(1,3,4,5)P4], and one inositol pentaphosphate [Ins(1,2,3,5,6)P5]. Some of these isomers [Ins(1,4,5)P3 and Ins(1,3,4,5)P4] are considered to play important biological roles in intracellular signaling.

Chromatography, High Pressure Liquid↗
PubMed1994

The mechanism of muscarinic agonist-stimulated inositol phosphate formation in permeabilized ileal smooth muscle.

Muscarinic agonists and guanylyl-5'-imidodiphosphate (Gpp(NH)p) stimulated formation of inositol phosphates in permeabilized longitudinal smooth muscle of guinea pig ileum. Gpp(NH)p markedly potentiated the formation of inositol bisphosphate (IP2) and inositol trisphosphate (IP3) stimulated by carbachol, but increased inositol monophosphate formation (IP1) only slightly. Gpp(NH)p enhanced the formation of IP2 + IP3 induced by either acetylcholine or carbachol about fourfold in a synergistic manner, but enhanced the effects of oxotremorine and pilocarpine less than twofold in an additive manner. Elevation of Ca2+ concentration resulted in increases of the inositol phosphate levels stimulated by both carbachol and Gpp(NH)p. The optimal concentration of Ca2+ for carbachol-stimulated formations of IP2 + IP3 was shifted to a lower Ca2+ concentration in the presence of Gpp(NH)p. These findings suggest that muscarinic receptor-stimulated polyphosphoinositide hydrolysis in ileal smooth muscle results in inositol polyphosphate formation via GTP binding protein (G-protein). The muscarinic receptor-activated G-protein decreases the Ca2+ requirement of polyphosphoinositide hydrolysis. Muscarinic agonists stimulate inositol polyphosphate formation by interaction of the G-protein activation of a phosphoinositide specific phospholipase C with Ca2+ influx.

Acetylcholine↗
PubMed1988

Demonstration of inositol phosphate 5-phosphomonoesterase activity in rabbit neutrophils: absence of a role for protein kinase C.

Rabbit peritoneal neutrophils, permeabilized with Triton X-100, contain inositol phosphate 5-phosphomonoesterase activity capable of converting [3H]inositol 1,4,5-trisphosphate (Ins-1,4,5-P3) to [3H]inositol 1,4-bisphosphate. This activity is found predominantly associated with the soluble component of fractionated neutrophils. It is comprised of specific and nonspecific activities toward Ins-1,4,5-P3 which can be separated by cation exchange chromatography. Treatment of neutrophils with phorbol 12-myristate 13-acetate (PMA) prior to permeabilization does not affect the rate of Ins-1,4,5-P3 breakdown by these cells. In addition, activation of endogenous protein kinase C in a soluble fraction prepared from neutrophils does not affect the specific inositol phosphate 5-phosphomonoesterase activity of this fraction. Taken together, these results provide evidence that activation of protein kinase C in the neutrophil does not affect its 5-phosphomonoesterase activity. Unlike platelets, the phosphorylation of a 5-phosphomonoesterase, if it occurs, may not play a role in the inhibitory effects of PMA on neutrophil responsiveness.

Animals↗
PubMed2001

Rapid analysis of inositol phosphates.

Fast and simple analytical methods for the determination of inositol bis- to hexakisphosphates or only inositol hexakisphosphate in foods and feces are presented. The methods are both faster and simpler with regard to analytical detection and sample pretreatment as compared to previously reported methods. The samples are pretreated using extraction and centrifugal ultrafiltration and analyzed using high-performance ion chromatography (HPIC) with gradient or isocratic elution. The analytes are detected using ultraviolet detection after postcolumn reaction. The methods are efficient, highly selective, and appropriate for analyzing inositol phosphates in food and feces samples. The between- and within-day variances were generally below 8 and 5% (relative standard deviation), respectively, for the presented HPIC method with gradient elution.

Chromatography, Ion Exchange↗
PubMed1987

ATP stimulates inositol phosphates accumulation and calcium mobilization in a primary culture of rat aortic myocytes.

The effects of extracellular ATP on phosphoinositide metabolism and intracellular Ca2+ concentration were studied in a primary culture of rat aortic myocytes. ATP increases the level of inositol phosphates, the putative second messenger for Ca2+ mobilization. No saturation of inositol phosphates accumulation is obtained (up to 10(-2) M ATP). Under the same conditions, ATP rapidly mobilizes intracellular Ca2+ in fura-2 loaded myocytes. The mobilization of intracellular Ca2+ is dose-dependent (maximal at 10(-4) M ATP), and is not affected by addition of EGTA. It is concluded that the receptors mediating the cytosolic increase of Ca2+ are of the P2-purinoceptor subtype. The physiological functions of these receptors are not presently known.

Adenosine Triphosphate↗
PubMed1986

Tumour promotor 12-O-tetradecanoylphorbol 13-acetate inhibits angiotensin II-induced inositol phosphate production and cytosolic Ca2+ rise in rat renal mesangial cells.

Preincubation of rat renal mesangial cells with 12-O-tetradecanoylphorbol 13-acetate (TPA) strongly inhibited the increases of inositol phosphates and of free cytosolic Ca2+ induced by angiotensin II (10(-7) M). TPA had no significant effect on the basal values of inositol phosphates and of free cytosolic Ca2+. Inhibition appeared already after 1 min and was maximal after 5 min. These effects occur without significant changes on angiotensin II binding in intact cells. The concentration of TPA needed (10(-9)-10(-7) M) was in the range believed to cause specifically an activation of protein kinase C. Furthermore the biologically inactive phorbol ester 4 alpha-phorbol 12,13-didecanoate was without effect. From the entirety of these results it is likely that protein kinase C inhibits angiotensin II activation of phospholipase C at a stage distal to receptor occupancy.

Angiotensin II↗