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1.
Pharmacological studies indicate that Syrian hamster melanoma (RPMI 1846) cells possess a melatonin binding site similar to that found in normal hamster cells. A high correlation was observed for a series of compounds between the Ki in hamster hypothalamic membranes vs. RPMI 1846 membranes (r = 0.94, slope = 0.93, P less than 0.01, n = 14). Scatchard analysis of saturation binding of 2-[125I]-iodomelatonin to membranes (at 0 degrees C) indicated: Kd = 0.89 +/- 0.08 nM, Bmax = 6.2 +/- 2.9 fmol/mg protein (n = 3). Melatonin did not alter basal or forskolin-stimulated adenylate cyclase activity in RPMI 1846 membranes or intact cells. Therefore, in contrast to the picomolar-affinity receptor for melatonin in the mammalian hypothalamus and pars tuberalis, the putative nanomolar-affinity receptor is not coupled to adenylate cyclase. The RPMI 1846 cell line provides a useful model system for further studies of signal transduction via the nanomolar-affinity site for melatonin. 相似文献
2.
Association of HL-A antigens andβ
2-microglobulin at the cellular and molecular level 总被引:1,自引:0,他引:1
Ralph A. Reisfeld Ernest D. Sevier Michele A. Pellegrino Soldano Ferrone Miroslav D. Poulik 《Immunogenetics》1975,2(1):183-197
Surfaces of cultured human lymphoid cells RPMI 1788, RPMI 4098, RPMI 8866, Raji, and WI-L2 were found to contain bothβ 2-microglobulin (β 2-μ) and HL-A determinants when tested by direct complement-dependent cytotoxicity andquantitative absorption with different cytotoxic antiβ 2-μ antisera and specific HL-A alloantisera. The same antigenic specificities were found in 3M KCl extracts of these cultured cells with a sensitiveβ 2-μ radioimmunoassay and an HL-A antigen blocking assay. Daudi cells provided a contrast, since noβ 2-μ or HL-A determinants were found on their surfaces or in 3 M KCl extracts prepared from them. Results from specific antibody blocking tests suggest a close association betweenβ 2-μ and HL-A determinants on plasma membranes of cultured human lymphoid cells. A solid state immunoadsorbent containing antiβ 2-μ antibodies effectively removed all detectable HL-A antigenic activity from some 3M KCl extracts of cultured human lymphoid cells as well as from some sera. Adsorption of HL-A antigens to these immunoadsorbents was specific since it was blocked only by prior addition ofβ 2-μ. Once on the antiβ 2-μ immunoadsorbents, HL-A antigens still reacted specifically with HL-A alloantibodies in quantitative absorption experiments. HL-A antigens andβ 2-μ could be eluted from antiβ 2-μ immunoadsorbents with a variety of chaotropic reagents and detergents, but thus far potassium bromide and sodium dodecyl sulfate (SDS) appear to be the most effective. SDS-PAGE of these eluates indicated that HL-A antigens were considerably purified by adsorption to antiβ 2-μ immunoadsorbents and that two major molecular size fragments were distinguishable, i.e., ∼33,000 for HL-A and ∼ 12,000 forβ 2-μ. 相似文献
3.
Abstract: The functional efficacies of inhibitors of l -glutamate uptake for altering second messenger formation in baby hamster kidney cells expressing subtypes mGluR1a, mGluR2, and mGluR4 of the metabotropic glutamate receptor family were examined. l -Serine-O-sulfate was an agonist at mGluR1a (EC50 = 70 µM), mGluR2 (EC50 = 25 µM), and mGluR4 (EC50 = 324 µM). l -Cysteine sulfinate, 1-aminocyclobutane-trans-1,3-dicarboxylate, l -cysteine, and dl -threo-3-methylaspartate stimulated phosphoinositide hydrolysis in mGluR1a cells with EC50 values of 43, 64, 463, and 488 µM, respectively, and displaced l -[3H]glutamate binding from membranes prepared from these cells with respective IC50 values of 48, 44, 79, and 139 µM. However, d -aspartate,l -trans-pyrrolidine-2,4-dicarboxylate, l -threo-3-hydroxyaspartate, and l -aspartate-β-hydroxamate stimulated phosphoinositide hydrolysis in mGluR1a cells (respective EC50 values of 73, 54, 57, and 430 µM) but did not displace l -[3H]glutamate binding. These compounds inhibited Na+-dependent l -glutamate uptake into baby hamster kidney cells with IC50 values similar to those for stimulation of phosphoinositide hydrolysis in mGluR1a cells. Phosphoinositide hydrolysis in mGluR1a cells, as stimulated by inhibitors of (or substrates for) this l -glutamate transporter, was significantly attenuated in the presence of l -glutamate decarboxylase (EC 4.1.1.15) or l -alanine aminotransferase (EC 2.6.1.2). Furthermore, incubation with 1 mMl -trans-pyrrolidine-2,4-dicarboxylate for 30 min increased the basal levels of free glutamate (1.5 ± 0.2 µM) in the assay buffer four- to fivefold as measured by HPLC analysis. Thus, heteroexchange with endogenous l -glutamate may lead to erroneous estimations of the functional efficacies at mGluR1a. 相似文献
4.
Cloned M1 muscarinic receptors mediate both adenylate cyclase inhibition and phosphoinositide turnover 总被引:4,自引:0,他引:4
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The rat M1 muscarinic receptor gene was cloned and expressed in a rat cell line lacking endogenous muscarinic receptors. Assignment of the cloned receptors to the M1 class was pharmacologically confirmed by their high affinity for the M1-selective muscarinic antagonist pirenzepine and low affinity for the M2-selective antagonist AF-DX-116. Guanylyl imidodiphosphate [Gpp(NH)p] converted agonist binding sites on the receptor, from high-affinity to the low-affinity state, thus indicating that the cloned receptors couple to endogenous G-proteins. The cloned receptors mediated both adenylate cyclase inhibition and phosphoinositide hydrolysis, but by different mechanisms. Pertussis toxin blocked the inhibition of adenylate cyclase (indicating coupling of the receptor to inhibitory G-protein), but did not affect phosphoinositide turnover. Furthermore, the stimulation of phosphoinositide hydrolysis was less efficient than the inhibition of adenylate cyclase. These findings demonstrate that cloned M1 receptors are capable of mediating multiple responses in the cell by coupling to different effectors, possibly to different G-proteins. 相似文献
5.
The Transplantable B-16 melanotic melanoma carried in syngeneic C57B1/6J female mice and the Syrian hamster melanoma cell line, RPMI 3460, were utilized to determine whether steroid-hormone receptors are present in animal melanomas. In the B-16 melanoma, a cytoplasmic-estrogen receptor is detectable, but there is no evidence for androgen or progestin receptors. Some tumors contain a glucocorticoid-binding macromolecule. Sucrosedensity gradient centrifugation of cytosol after incubation with [3H]-estradiol revealed an 8S peak that was suppressed by excess radioinert diethylstilbesterol. Binding varied from 5–35 fmoles per mg cytosol protein. Scatchard analysis of [3H]-estradiol binding in cytosol yielded a single class of high-affinity binding sites; the dissociation constant is 6 × 10?10 M. The receptor molecule is shown to be estrogen-specific by ligand competition assays. In contrast to B-16 melanoma, no estrogen, androgen, or progestin receptor can be found in the Syrian hamster melanoma cell line. However, a substantial level of specific binding is observed using [3H]-dexamethasone. Sucrose-gradient centrifugation of cytosol from this cell line after incubation with [3H]-dexamethasone revealed a 7S peak that was suppressed by excess radioinert dexamethasone. Scatchard analysis indicated a single class of high affinity sites with a dissociation constant of 2 × 10?9 M. Binding levels from 70–610 fmoles per mg cytosol protein were observed. The Syrian hamster melanoma cells also exhibit a biological response to glucocorticoids: Dexamethasone causes both an inhibition of growth and a decrease in final-cell density in these cells. 相似文献
6.
The effect of melatonin (5-methoxy-N-acetyltryptamine) on microtubule assembly was assessed by means of viscometry, cell kinetics and [3H]colchicine binding studies. Evidence presented shows that melatonin has no effect on the in vitro assembly of bovine brain microtubules. [3H]Colchicine binding is not inhibited by melatonin in either crude or purified tubulin preparations. Furthermore, no increase in mitotic index is observed when Chinese hamster ovary cells are treated with melatonin; nor is neurite formation in neurobiastoma cells in culture affected by melatonin. It is concluded that melatonin does not interact with microtubules in a manner similar to colchicine and the Vinca alkaloids and it should not be classified as a colchicine-like mitotic inhibitor. 相似文献
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9.
OBJECTIVES: The aim of this study was to examine the effects of melatonin as well as of its precursor (N-acetylserotonin) and metabolite (6-hydroxymelatonin) on the ultrastructure of the pinealocytes of the Syrian hamster. MATERIAL AND METHODS: The pineal glands of 2-month-old male Syrian hamsters were examined. The animals were divided into the following groups of four animals each: group 1 - melatonin treatment; group 2 - N-acetylserotonin treatment; group 3 - 6-hydroxymelatonin treatment (all substances given subcutaneously at doses of 25 microg per animal between 16.00 and 17.00 h daily for seven weeks). Group 4 was given solvent treatment only and served as controls. The animals were killed by decapitation between 09:00 and 10.00 h. Routine electron microscopical techniques were used to obtain quantitative data on pinealocyte ultrastructure. RESULTS: Melatonin administration did not influence the size of the hamster pinealocytes, whereas administration of N-acetylserotonin and 6-hydroxymelatonin caused a significant reduction in cell size in comparison to the melatonin-treated and control groups. There were changes in the relative volumes of the mitochondria, Golgi apparatus and lysosomes in the pinealocytes of the studied groups, while the volumes of granular endoplasmic reticulum and lipid droplets were unchanged. The dense-core vesicles were more numerous in the pinealocytes of the melatonin and 6-hydroxymelatonin-treated groups in comparison to those of animals treated with N-acetylserotonin or the controls. CONCLUSIONS: The changes observed in the ultrastructure of hamster pinealocytes indicate that administration of melatonin as well as of its precursor or metabolite influences the morphology of these cells and also, perhaps, their secretory activity. 相似文献
10.
《Mutation Research/Genetic Toxicology》1996,367(2):99-104
The purpose of this study is to explore the mutual interactions among the chemical ingredients of betel quid including arecoline, sodium fluoride, catechin and glycyrrhizin in producing genotoxicity on Chinese hamster ovary (CHO) cells using the micronucleus method. Our results show that arecoline at a rather low concentration of 0.2–2 μM which could be in the oral cavity during betel quid chewing and NaF (0.8–2.4 mM) significantly elevated the number of micronucleated cells in a concentration-dependent manner. In addition, significant prolongation of cell cycles was observed by treatment with arecoline (≥2.0 μM) or NaF (2.4 mM) in CHO cells. Both catechin and glycyrrhizin could antagonize not only the increased micronucleated cells induced by arecoline and NaF but also the prolonged cell cycle induced by arecoline in CHO cells. This finding implies that the adjuvant ingredients, catechu and liquorice root extract provide not only a flavor but also an antagonist against the genotoxicity of arecoline and fluoride containing betel quid. 相似文献
11.
Robert J. Deschenes Dana C. Hilt Judith K. Marquis Henry G. Mautner 《生物化学与生物物理学报:生物膜》1981,641(1):166-172
Tb3+, a fluorescent trivalent cation with physicochemical properties similar to Ca2+, binds to peripheral nerve membrane vesicles prepared from the walking leg nerve bundle of the lobster (Homarus americanus). Saturable binding is measured for at least two classes of binding site. Bound Tb3+ can be displaced by other cations in the order: Ca2+ > Mg2+ = Zn2+ > NH4+. The binding of Tb3+ to the lower affinity site (KD(app) = 6.0 μM) is inhibitable by Na+, Mg2+ and Ca2+, whereas the higher affinity site (KD(app) = 2.2 μM) is only sensitive to Ca2+. Using this spectral probe the role of Ca2+ in peripheral nerve membrane function can be investigated. 相似文献
12.
We have shown that morpholine, a cyclic amine, exerts a selective inhibition of growth on melanocytic pigmented cell lines compared to nonpigmented cells. The ID50 of morpholine for the pigmented B-16 cell line HFH was 1200 micrograms/ml, compared to values greater than 2400 micrograms/ml for baby hamster kidney, Chinese hamster ovary and NP, an unpigmented primate cell line. Two other cyclic amines piperazine and piperidine, were similarly found to be selectively toxic to melanocytes. This selective toxicity could be synergistically enhanced by pretreatment of the cells with theophylline, a stimulator of tyrosinase activity, which indicates that the selective toxicity may be associated with melanin synthesis. Low passage HFH, high passage HFH and Syrian hamster melanoma RPMI 1846 cells that were pretreated with theophylline showed between 13 and 29% greater toxicity compared to controls treated with theophylline or morpholine alone. Unpigmented NP primate cells, Chinese hamster ovary and mouse fibroblast L929 remained unaffected. These cyclic amines join a list of other amines that have also been shown to be melanocytotoxic. 相似文献
13.
Muscarinic-stimulated norepinephrine release and phosphoinositide hydrolysis in PC12 cells are independent events 总被引:2,自引:0,他引:2
This laboratory has reported recently that muscarinic receptor-stimulated release of norepinephrine from pheochromocytoma (PC12) cells is dependent upon an influx of Ca2+ through a Ca2+ channel that is regulated by a pertussis toxin-sensitive GTP-binding protein (G-protein) (Inoue, K., and Kenimer J. G. (1988) J. Biol. Chem. 263, 8157-8161). In the present study, we have examined the role of phosphoinositide hydrolysis in this mechanism. The muscarinic agonist methacholine was shown to stimulate phosphoinositide hydrolysis by a mechanism that was sensitive to pertussis toxin inhibition. When assayed in the absence of Ca2+, muscarinic-stimulated norepinephrine release but not phosphoinositide hydrolysis was blocked. Conversely, muscarinic-stimulated phosphoinositide hydrolysis but not norepinephrine release was blocked in cells preincubated with phorbol 12,13-dibutyrate. In contrast to several previous hypotheses that suggested that muscarinic-stimulated neurotransmitter release is dependent upon phosphoinositide hydrolysis, our results suggest that these two muscarinic-stimulated processes are independent events in PC12 cells. Inhibition studies with muscarinic receptor subtype-specific antagonists suggest that norepinephrine release is regulated by an M2 subtype muscarinic receptor and that phosphoinositide hydrolysis is regulated by an M3 subtype muscarinic receptor. 相似文献
14.
The ganglioside GM4 is a sialic acid-containing glycosphingolipid mainly expressed in mammalian brain and erythrocytes. GM4 is synthesized by the sialylation of galactosylceramide (GalCer), while the ganglioside GM3 is synthesized by the sialylation of lactosylceramide (LacCer). Recently, the enzyme GM3 synthase was found to be responsible for the synthesis of GM4 in vitro and in vivo, yet the mechanism behind GM4 expression in cells remains unclear. In this study, we attempted to establish GM4-reconstituted cells to reveal the regulation of GM4 synthesis. Interestingly, GM4 was not detected in RPMI 1846 cells expressing LacCer, GalCer, and GM3. Similarly, GM4 was not detected in CHO-K1 cells, even when such cells expressing LacCer and GM3 were stably transfected with the GalCer synthase (GalCerS) gene. GM4 became detectable only when the GM3/GM4 synthase (GM3/GM4S, ST3GAL5) gene was overexpressed in either RPMI 1846 or CHO-K1/GalCerS cells. A mutant of the B16 melanoma cell line, GM-95, lacks GlcCer and LacCer, due to an absence of GlcCer synthase, but carries endogenous LacCer synthase and GM3/GM4S. GalCer became detectable after transfection of GalCerS into GM95 cells, but the GM95/GalCerS reconstituted cells did not express GM4, indicating that competition between the substrates LacCer and GalCer for GM3/GM4S does not cause the failure of GM4 synthesis. These results suggest that the expression machinery of GM4 under physiological conditions is independent from that of GM3. 相似文献
15.
Tatyana A. Zykova Feng Zhu Tatyana I. Vakorina Jishuai Zhang Lee Ann Higgins Darya V. Urusova Ann M. Bode Zigang Dong 《The Journal of biological chemistry》2010,285(38):29138-29146
Protein kinases are potential targets for the prevention and control of UV-induced skin cancer. T-cell-originated protein kinase (TOPK) is highly expressed in skin cancer cells, but its specific function is still unknown. We investigated the role of TOPK in UVB-induced apoptosis in RPMI7951 human melanoma cells. Liquid chromatography-tandem mass spectrometry analysis was used to identify proteins that bind with TOPK. Immunofluorescence, Western blot, and flow cytometry were used to assess the effect of UVB on TOPK, peroxiredoxin 1 (Prx1), and apoptosis in RPMI7951 cells. TOPK binds with Prx1 and its phosphorylation of Prx1 at Ser-32 is important for regulation of H2O2-mediated signal transduction. Analysis of the CD spectra of Prx1 and mutant Prx1 (S32A) proteins showed that the secondary structure of Prx1 was significantly altered by phosphorylation of Prx1 at Ser-32. UVB irradiation induced phosphorylation of TOPK in RPMI7951 human melanoma cells and phosphorylated TOPK co-localized with Prx1 in the nucleus. UVB induced the peroxidase activity of Prx1 in vitro and ex vivo. Following treatment with UVB, H2O2 levels and apoptosis were increased in RPMI7951 cells stably expressing TOPK siRNA or stably mutant Prx1 (S32A). Phosphorylation of Prx1 (Ser-32) by TOPK prevents UVB-induced apoptosis in RPMI7951 melanoma cells through regulation of Prx1 peroxidase activity and blockade of intracellular H2O2 accumulation. 相似文献
16.
(1) The effects of calmodulin binding on the rates of Ca2+-dependent phosphorylation and dephosphorylation of the red-cell Ca2+ pump, have been tested in membranes stripped of endogenous calmodulin or recombined with purified calmodulin. (2) In Mg2+-containing media, phosphorylation and dephosphorylation rates are accelerated by a large factor (at 0°C), but the steady-state level of phosphoenzyme is unaffected by calmodulin binding (at 0°C and 37°C). In Mg2+-free media, slower rates of phosphoenzyme formation and hydrolysis are observed, but both rates and the steady-state phosphoenzyme level are raised following calmodulin binding. (3) At 37°C and 0°C, the rate of (Ca2+ + Mg2+)-ATPase activity is stimulated maximally by 6–7-fold, following calmodulin binding. At 37°C the apparent Ca2+ affinity for sustaining ATP hydrolysis is raised at least 20-fold, Km(Ca) ? 10 μM (—calmodulin) and Km(Ca) < 0.5 μM (+ calmodulin), but at 0°C the apparent Ca2+ affinity is very high in calmodulin-stripped membranes and little or no effect of calmodulin is observed (Km(Ca) ? 3–4 · 10-8 M). (Ca2+ + Mg2+)-ATPase activity in calmodulin activated membranes and at saturating ATP levels, is sharply inhibited by addition of calcium in the range 50–2000 μM. (4) A systematic study of the effects of the nucleotide species MgATP, CaATP and free ATP on (Ca2+ + Mg2+)-ATPase activity in calmodulin-activated membranes reveals: (a) In the 1–10 μmolar concentration range MgATP, CaATP and free ATP appear to sustain (Ca2+ + Mg2+)-ATPase activity equally effectively. (b) In the range 100–2000 μM, MgATP accelerates ATP hydrolysis (Km(MgATP) ? 360 μM), and CaATP is an inhibitor (Ki(CaATP) ? 165 μM), probably competing with MgATP fo the regulatory site. (5) The results suggest that calmodulin binding alters the conformational state of the Ca2+- pump active site, producing a high (Ca2+ + Mg2+)-ATPase activity, high Ca2+ affinity and regulation of activity by MgATP. 相似文献
17.
Kee Hun Do Young Whan Choi Eun Kyoung Kim Sung Ji Yun Min Sung Kim Sun Young Lee Jung Min Ha Jae Ho Kim Chi Dae Kim Beung Gu Son Jum Soon Kang Ikhlas A. Khan Sun Sik Bae 《Phytomedicine》2009,16(6-7):530-537
Lignans are major constituents of plant extracts and have important pharmacological effects on mammalian cells. Here we showed that pinoresinol-4,4′-di-O-β-d-glucoside (PDG) from Valeriana officinalis induced calcium mobilization and cell migration through the activation of lysophosphatidic acid (LPA) receptor subtypes. Stimulation of mouse embryo fibroblast (MEF) cells with 10 μM PDG resulted in strong stimulation of MEF cell migration and the EC50 was about 2 μM. Pretreatment with pertussis toxin (PTX), an inhibitor of Gi protein, completely blocked PDG-induced cell migration demonstrating that PDG evokes MEF cell migration through the activation of the Gi-coupled receptor. Furthermore, pretreatment of MEF cells with Ki16425 (10 μM), which is a selective antagonist for LPA1 and LPA3 receptors, completely blocked PDG-induced cell migration. Likewise, PDG strongly induced calcium mobilization, which was also blocked by Ki16425 in a dose-dependent manner. Prior occupation of the LPA receptor with LPA itself completely blocked PDG-induced calcium mobilization. Finally, PDG-induced MEF cell migration was attenuated by pretreatment with a phosphatidylinositol 3-kinase (PI3K) inhibitor such as LY294002. Cells lacking downstream mediator of PI3K such as Akt1 and Akt2 (DKO cells) showed loss of PDG-induced migration. Re-expression of Akt1 (but not Akt2) completely restored PDG-induced DKO cell migration. Given these results, we conclude that PDG is a strong inducer of cell migration. We suggest that the pharmacological action of PDG may occur through the activation of an LPA receptor whereby activation of PI3K/Akt signaling pathway mediates PDG-induced MEF cell migration. 相似文献
18.
Muscarinic agonists stimulated arachidonic acid release from 10- to 32-fold in Chinese hamster ovary (CHO) cells transfected with muscarinic M1, M3 and M5 receptor subtypes. Muscarinic agonists liberated arachidonic acid from the cAMP-coupled M2 and M4 cells only in the presence of ATP. Partial agonists were less efficacious at liberating arachidonic acid than full agonists. The ability of muscarinic agonists to liberate arachidonic acid and stimulate phosphoinositide hydrolysis in the same CHO M1, M3 and M5 cells was well correlated; however, partial agonists were more efficacious at stimulating phosphoinositide hydrolysis than arachidonic acid release. The efficacy and potency of 13 muscarinic agonists to liberate arachidonic acid was characterised. Influx of external calcium was required for arachidonic acid release even after initiation of agonist-induced release. It is concluded that arachidonic acid release is a simple assay suitable for evaluation of muscarinic agonists, antagonists and the flux of external calcium into cells. 相似文献
19.
《Journal of receptor and signal transduction research》2013,33(5):623-645
AbstractWe have shown that binding of 3H-dihydroalprenolol ([3H] DHA) to DDT1 MF-2 cells and cell membranes was of high affinity, saturable, stereoselective and reversible. The [3H]DHA dissociation constants were 0.63 ± 0.15 nM (n=6) and 0.83 ± 0.04 nM (n=5) for intact cells and cell membranes, respectively, with a binding site concentration for cells of 27,300 ± 5,200 sites/ cell (n=6) and for membranes 468 ± 24 fmoles/mg protein (n=5). The order of agonist competition for the [3H]-DHA binding site of DDT1 cell membranes was isoproterenol (Ki = 0.20 ± 0.07 μM) > epinephrine (Ki = 0.4 ± 0.2 μM) > norepinephrine (Ki = 66.5 ± 5.15 μM) consistent with a β2-selective receptor interaction. Zinterol, a β2-selective antagonist, (Ki = 0.05 ± 0.01 μM) was 18x more effective than metoprolol, a β1-selective antagonist (Ki = 0.9 ± 0.1 μM), in competing for the DHA binding site. A nonlinear iterative curve fitting analysis of zinterol and metoprolol binding isotherms indicated that (p>0.05) DDT1 cells possess a pure population of β2-adrenergic receptors. Finally, we have shown that DDT1 MF-2 cell β2-adrenergic receptor is functionally coupled to adenylate cyclase via a G/F protein complex as demonstrated in part by a guanine nucleotide requirement for isoproterenol stimulation of adenylate cyclase activity. In addition, guanine nucleotide mediated a reduction in the affinities of isoproterenol and epinephrine for the [3H]DHA binding site. 相似文献
20.
R Gyurko B Kimura P Kurian F T Crews M I Phillips 《Biochemical and biophysical research communications》1992,186(1):285-292
Among the many functions of angiotensin II (Ang II) it now appears that Ang II is a growth factor. The concentration of Ang II in rat skin has been shown to increase during wound healing. To investigate the intracellular effect of Ang II in skin we determined the levels of total cytoplasmic inositol phosphates after incubation of skin slices with different doses of Ang II. 10(-6) M of Ang II increased significantly the phosphatidylinositol (PI) hydrolysis, and the effect was dose dependent up to 10(-4) M Ang II. The majority of inositol phosphates yielded after 1 hour incubation in the presence of lithium was InsP1, with lesser amount of InsP2. Losartan, the Ang II AT1 antagonist, at a dose of 10(-4) M blocked the effect of Ang II, while PD123319, the Ang II AT2 antagonist, had no antagonistic action; PD123319 at the higher dose of 10(-3) M, however, potentiated the effect of Ang II on PI hydrolysis. The results suggest that PI hydrolysis is a second messenger system for Ang II in rat skin. Also, the two subtypes of Ang II receptors mediate opposite effects on PI hydrolysis: Ang II binding to AT1 receptors increases inositol phosphate production, while Ang II binding to AT2 receptors decreases inositol phosphate production. 相似文献