Characterization of Cbl tyrosine phosphorylation and a Cbl-Syk complex in RBL-2H3 cells

Tyrosine phosphorylation of the Cbl protooncogene has been shown to occur after engagement of a number of different receptors on hematopoietic cells. However, the mechanisms by which these receptors induce Cbl tyrosine phosphorylation are poorly understood. Here we demonstrate that engagement of the high affinity IgE receptor (Fc epsilon R1) leads to the tyrosine phosphorylation of Cbl and analyze how this occurs. We show that at least part of Fc epsilon R1-induced Cbl tyrosine phosphorylation is mediated by the Syk tyrosine kinase, and that the Syk-dependent tyrosine phosphorylation of Cbl occurs mainly distal to the Cbl proline-rich region within the COOH-terminal 250 amino acids. Furthermore, we show by coprecipitation that Cbl is present in a complex with Syk before receptor engagement, that the proline-rich region of Cbl and a region of Syk comprised of the two SH2 domains and intradomain linker are required for formation of the complex, and that little or no tyrosine-phosphorylated Cbl is detected in complex with Syk. Overexpression of truncation mutants of Cbl capable of binding Syk has the effect of blocking tyrosine phosphorylation of endogenous Cbl. These results define a potentially important intramolecular interaction in mast cells and suggest a complex function for Cbl in intracellular signaling pathways.     

The production of tumor necrosis factor-alpha by rat basophilic leukemia cells with triggering IgE receptor

We evaluated cytotoxic factor released from rat basophilic leukemia cells (RBL) sensitized with anti-ovalbumin (OVA) mouse serum after incubation with OVA. The cytotoxic activity of this factor was completely blocked by anti-mouse tumor necrosis factor-alpha (mTNF-alpha) specific antibody. Therefore, we concluded that by triggering the IgE receptor, RBL could produce and release TNF-alpha.     

Changes in histidine uptake and histamine synthesis during the growth cycle of rat basophilic leukemia (2H3) cells

Rat basophil leukemia (2H3) cells, like normal rat peritoneal mast cells, were shown to take up and decarboxylate histidine. Uptake was mediated by a temperature-dependent system with high affinity (apparent Km 24 +/- 4 microM) for histidine. Newly formed histamine was incorporated into the intracellular pool of histamine. In confluent cultures, substantial amounts of histamine were lost to the medium while intracellular histamine levels remained constant. As calculated from the rate of appearance of histamine in the medium, the maximum turnover time for the intracellular histamine pool (2-7 nmol/10(6) cells) was about 12 hr. Variation in histamine content, histidine uptake and histidine decarboxylation was noted with different passages of 2H3 cells, but with all passages there were characteristic changes in these parameters during growth and division of the cells. Separation of cells into fractions of different size by elutriation indicated low rates of histidine uptake and decarboxylation in the smallest 2H3 cells, a progressive increase in ability to take up and decarboxylate histidine as the cells approached the S phase of growth and marked decline in this ability in fractions containing the larger cells. The changes in kinetic constants suggested that fluctuation in histidine uptake during the life cycle of the 2H3 cell was due to changes in the number of active carriers or sites of histidine transport and that during cell division all components associated with histamine synthesis (i.e., histidine uptake and decarboxylation) were diminished.     

大鼠RBL-2H3细胞瞬时感受器电位M7通道参与细胞存活及凋亡

背景：瞬时感受器电位M7是肥大细胞上重要的钙离子通道,但其在肥大细胞存活及凋亡过程中的作用仍未明确。目的：观察瞬时感受器电位M7通道对大鼠RBL-2H3细胞存活及凋亡的影响。方法：取对数生长期RBL-2H3细胞,①分别以50,100,200μmol/L瞬时感受器电位通道阻断剂2-APB进行干预,并以0.1%DMSO干预的细胞及正常培养的细胞作对照。②以瞬时感受器电位M7-siRNA反转录病毒载体转染RBL-2H3细胞,并设立空载体组和正常对照组。结果与结论：经过100,200μmol/L的2-APB作用72h后,RBL-2H3细胞数减少,吸光度值降低（P〈0.05）,细胞凋亡增多,早期凋亡率和总凋亡率增加（P〈0.05）;RBL-2H3细胞转染si-瞬时感受器电位M772h后,吸光度值降低（P〈0.05）,细胞凋亡增多,早期凋亡率和总凋亡率增加（P〈0.05）。说明瞬时感受器电位M7通道参与了RBL-2H3细胞存活和凋亡过程。     

大鼠RBL-2H3细胞瞬时感受器电位M7通道参与细胞存活及凋亡

背景:瞬时感受器电位M7是肥大细胞上重要的钙离子通道,但其在肥大细胞存活及凋亡过程中的作用仍未明确。目的:观察瞬时感受器电位M7通道对大鼠RBL-2H3细胞存活及凋亡的影响。方法:取对数生长期RBL-2H3细胞,①分别以50,100,200μmol/L瞬时感受器电位通道阻断剂2-APB进行干预,并以0.1%DMSO干预的细胞及正常培养的细胞作对照。②以瞬时感受器电位M7-siRNA反转录病毒载体转染RBL-2H3细胞,并设立空载体组和正常对照组。结果与结论:经过100,200μmol/L的2-APB作用72h后,RBL-2H3细胞数减少,吸光度值降低(P<0.05),细胞凋亡增多,早期凋亡率和总凋亡率增加(P<0.05);RBL-2H3细胞转染si-瞬时感受器电位M772h后,吸光度值降低(P<0.05),细胞凋亡增多,早期凋亡率和总凋亡率增加(P<0.05)。说明瞬时感受器电位M7通道参与了RBL-2H3细胞存活和凋亡过程。     

Cell cycle-associated changes in receptors for IgE during growth and differentiation of a rat basophilic leukemia cell line

The rat basophilic leukemia cell line (RBL-1) showed an inverse relationship between growth rate and expression of receptor activity for IgE. After prolonged exponential growth, the number of receptors per cell stabilized at 4-6 times 10-5. Cells in stationary cultures, which are arrested in the G1 phase of the cell cycle, continued to accumulate up to 0.9-1.7 times 10-6 receptors/cell with no increase in volume. Upon resuspension in fresh medium at low density, these cells were shown to lose up to 70% of the receptor activity within 4 h. Assessment of cultures synchronized by double thymidine block and cells fractionated by centrifugation of a Ficoll gradient indicated that the RBL-1 cells acquire receptors in the G1 phase of the cell cycle. No accumulation of active receptors occurred during the S and G2 phases, though the average cell volume increased. Cell division resulted in a drop in number of receptors per cell while the number of cell-bound receptors in the culture remained unchanged. This indicates that during mitosis receptors were simply distributed to daughter cells.     

Carrier-mediated uptake of the endogenous cannabinoid anandamide in RBL-2H3 cells

Anandamide (N-arachidonylethanolamide) is an endogenous cannabinoid that mimics the pharmacologic effects of Delta(9)-tetrahydrocannabinol, the major bioactive substance in marijuana. Anandamide appears to be synthesized, released, and inactivated by mechanisms similar to those for other neurotransmitters. Of interest to the present studies are reports that anandamide undergoes carrier-mediated uptake into neuronal or glial cells after release, followed by rapid intracellular degradation by the intracellular fatty acid amidohydrolase. In addition to effects in the brain, anandamide has multiple effects in the periphery, particularly on cells of the immune system that express both a peripheral cannabinoid receptor and amidohydrolase enzyme. We have performed a detailed characterization of anandamide uptake in the cognate mast cell line RBL-2H3 to test the hypothesis that the uptake system in peripheral cells is also carrier-mediated and functionally similar to that observed in the central nervous system. RBL-2H3 cells exhibited robust, saturable transport of [(3)H]anandamide that was both time- and temperature-sensitive. This transport activity was not dependent on extracellular ion gradients for uptake and was inhibited selectively by other fatty acid-derived molecules, anandamide congeners, and the psychoactive cannabinoids such as Delta(9)-tetrahydrocannabinol. We conclude that anandamide transport in the RBL-2H3 cells is carrier-mediated, and uptake in peripheral cells is functionally and pharmacologically identical with that observed in neurons and astrocytes.     

Methylxanthines block antigen-induced responses in RBL-2H3 cells independently of adenosine receptors or cyclic AMP: evidence for inhibition of antigen binding to IgE.

Activation of a novel adenosine receptor in a rat tumor mast cell line (RBL-2H3 cells) elicits a transient generation of inositol 1,4,5-trisphosphate and an equally transient increase in the level of free cytosol Ca++: Such responses promote little exocytosis, but markedly enhance the secretory response to antigen. A variety of xanthine adenosine receptor antagonists did not suppress the responses to the adenosine analog 5-N-ethylcarboxamidoadenosine. However, 3-isobutyl-1-methylxanthine (IBMX) and certain related xanthines inhibited antigen (dinitrophenylated bovine serum albumin, DNP-BSA)-induced generation of inositol phosphates, the increase in level of free cytosolic Ca++ and exocytosis in RBL-2H3 cells that were primed with a monoclonal DNP-specific immunoglobulin E (from hybridoma H1 DNP-epsilon-26.82). The same compounds inhibited the binding of antigen to cell attached DNP-specific IgE in a highly selective manner. Incorporation of an aromatic or cycloalkyl group in the 8-position of IBMX or theophylline, for example, resulted in compounds that were more potent inhibitors than the parent compounds. Conversely, substituents in the 7- or 9-position of IBMX resulted in inactive compounds. 1,3-Diethylxanthine and 1,3-dipropylxanthine had no activity, suggesting that substituents as large as ethyl or propyl are not tolerated at the 1-position. Inhibition by IBMX was not observed when cells were activated by nonimmunological stimulants or when cells were primed with certain other monoclonal preparations of DNP-specific IgE and stimulated by DNP-BSA.(ABSTRACT TRUNCATED AT 250 WORDS)     

TA-270 [4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone], an anti-asthmatic agent,inhibits leukotriene production induced by IgE receptor stimulation in RBL-2H3 cells

A novel quinolinone derivative, TA-270 [4-hydroxy-1-methyl-3-octyloxy-7-sinapinoylamino-2(1H)-quinolinone], has been shown to inhibit antigen-induced asthmatic responses including the early-phase bronchoconstriction in actively sensitized guinea pigs. Here we characterized the action mechanisms of TA-270 in cellular level in vitro. In RBL-2H3 mast cells sensitized with dinitrophenol (DNP)-specific IgE, the antigen exhibited several mast cell functions, including hexosaminidase release as a marker of degranulation, production of tumor necrosis factor-alpha, and production of immunologically detective leukotrienes. These antigen-induced actions were associated with the activation of several early signaling events, including inositol phosphate production reflecting phospholipase C activation and extracellular signal-regulated kinase activation. When the cells were treated with TA-270, the antigen-induced leukotriene production was almost completely suppressed, but other antigen-induced actions listed above were hardly affected. This drug also failed to affect the antigen-induced phospholipase A2 activation as evaluated by the total release of arachidonic acid and its metabolites from the cells prelabeled with radioactive arachidonic acid. However, TA-270 clearly changed the arachidonic acid metabolic pathway. It suppressed the accumulation of 5-lipoxygenase products, including leukotrienes, but hardly affected the accumulation of cyclooxygenase products. The inhibitory action of TA-270 on leukotriene production was also observed in human neutrophils and eosinophils. We conclude that TA-270 inhibits 5-lipoxygenase activity and, thereby, suppresses the antigen-induced leukotriene production.     

反转录病毒介导靶向瞬时感受器电位M7基因siRNA抑制RBL-2H3细胞的活化

背景:钙离子在肥大细胞活化后的脱颗粒反应起重要作用。瞬时感受器电位M7(transient receptor potential melastatin7,TRPM7)是肥大细胞重要的候选通道。目的:构建携带大鼠靶向TRPM7-siRNA的反转录病毒载体并检测其对大鼠RBL-2H3细胞抗原活化的影响。方法:实验设计3个TRPM7-siRNA序列和1个无关对照序列,克隆到酶切的pSuper-retro-neo-GFP反转录病毒载体,用重组质粒pSuper-retro-neo-GFP-shTRPM7-(1,2,3)采用脂质体Lipofectamine 2000转染RBL-2H3细胞,采用Western blot检测干扰效率。筛选出最有效的pSuper-retro-neo-GFP-siTRMP7与包装质粒共转染293FT细胞生成反转录病毒并感染RBL-2H3细胞,荧光实时定量PCR及Western blot检测TRPM7-siRNA的沉默效果。检测β-氨基已糖苷酶活性探讨RBL-2H3细胞抗原活化程度的改变。结果与结论:转染后的各组细胞中siTRPM7-3转染组的沉默效率最高(P<0.05)。pSuper-retro-neo-GFP-siTRMP7-3干扰组的TRPM7基因的mRNA水平和蛋白水平显著下调,致敏后其β-氨基已糖苷酶活性明显降低(P<0.05)。结果提示,降低TRPM7基因的表达可抑制RBL-2H3细胞的抗原活化。     

A role for Bruton's tyrosine kinase in B cell antigen receptor-mediated activation of phospholipase C-gamma 2

Defects in the gene encoding Bruton's tyrosine kinase (Btk) result in a disease called X-linked agammaglobulinemia, in which there is a profound decrease of mature B cells due to a block in B cell development. Recent studies have shown that Btk is tyrosine phosphorylated and activated upon B cell antigen receptor (BCR) stimulation. To elucidate the functions of this kinase, we examined BCR signaling of DT40 B cells deficient in Btk. Tyrosine phosphorylation of phospholipase C (PLC)-gamma 2 upon receptor stimulation was significantly reduced in the mutant cells, leading to the loss of both BCR-coupled phosphatidylinositol hydrolysis and calcium mobilization. Pleckstrin homology and Src-homology 2 domains of Btk were required for PLC-gamma 2 activation. Since Syk is also required for the BCR-induced PLC-gamma 2 activation, our findings indicate that PLC-gamma 2 activation is regulated by Btk and Syk through their concerted actions.     

β淀粉样蛋白对神经干细胞酪氨酸蛋白激酶A表达的影响

目的:观察不同浓度的Aβ1-40对C17.2神经干细胞TrkA表达的影响方法:分别应用舍终浓度为0、20、40、60、80、100 nmol/L Aβ1-40的培养液孵育C17.2神经干细胞24 h,MTT法检测各组细胞活性,Western blot观察各组神经干细胞TrkA表达情况.结果:MTT法检测结果显示各组细胞活性差异不明显;Western blot结果显示终浓度为20、40、60 nmol/L Aβ1-40组的神经干细胞TrkA表达有不同程度的增加,100 nmol/L Aβ1-40组细胞TrkA表达较对照组减少,80 nmol/L Aβ1-40组细胞TrkA表达较对照组差异无统计学意义.结论:Aβ1-40对神经干细胞TrkA表达的影响呈浓度依赖性.     

Characterization of [5,6-3H]SQ 29,548 as a high affinity radioligand, binding to thromboxane A2/prostaglandin H2-receptors in human platelets

The binding of 5,6-3H(1S-[1 alpha, 2 beta(5Z), 3 beta, 4 alpha])-7-[3-([2-[(phenyl amino)carbonyl]hydrazino]methyl)-7-oxabicyclo[2.2.1]hept-2-yl]-5- heptenoic acid to receptors in human washed platelets (WP) and platelet membranes (PM) was characterized with regard to kinetics, saturability and competitive inhibition by putative thromboxane A2/prostaglandin H2 (TP)-receptor ligands. Specific binding of [3H]SQ 29,548 routinely amounted to 90 to 97% of total binding. The rate of association was 1.6 x 10(7) and 2.5 x 10(7) M-1 x min-1 in WP and PM, respectively. The corresponding rate of dissociation was 0.07 and 0.12 min-1, resulting in dissociation constants of 4.1 and 5.8 nM in WP and PM, respectively. Saturable binding to a single class of receptors indicated a receptor density of 2633 fmol/mg of protein in WP (1394 receptors/platelet; kd, 4.5 nM) and 1466 fmol/mg of protein in PM (kd, 11.3 nM). Specific binding of [3H]SQ 29,548 was inhibited by five antagonists (high/low affinity kd values in nanomolar), SQ 29,548 (WP, 5.2; PM, 7.3), SQ 28,668 (WP, 32; PM, 73), SQ 30,741 (WP, 28; PM, 50), BM 13,177 (WP, 140; PM, 4834) and BM 13,505 (WP, 5/379; PM, 11). Two agonists, U 44069 and U 46619, inhibited the binding in a biphasic manner, indicating binding to two receptor sites (approximately 20/80%) with kd values of 4/72 and 4/170 nM, respectively, in WP and 7/136 and 19/502 nM, respectively in PM. The demonstrated high affinity binding of [3H]SQ 29,548 to human platelet TP-receptors should make this radioligand a suitable and potentially useful tool in future studies of function, structure and regulation of TP-receptors.     

Specific, high affinity [3H]ethylketocyclazocine binding in rat central nervous system: lack of evidence for kappa receptors

The binding properties and distribution of the tritiated benzomorphan, [3H]ethylketocyclazocine, were studied in rat central nervous system (CNS). Specific binding is saturable and represents 75 to 90% of total binding. Scatchard analysis is consistent with the existence of two classes of binding sites with Kd values of 0.5 and 10.5 nM, respectively. Ethylketocyclazocine binding is increased in the presence of sodium chloride. This characteristic resembles that of opiate antagonists rather than that of other agonists. The distribution of ligands. The IC50 values of various opioid agonists and antagonists for competition with [3H]ethylketocyclazocine correlate well with their IC50 values for competition with [3H]naloxone. This evidence does not lend support to the existence of a separate kappa receptor in rat CNS.     

As2O3对K562细胞BCR/ABL蛋白酪氨酸磷酸化的影响

目的　进一步阐明Ａｓ２Ｏ３ 诱导Ｋ５６２ 细胞凋亡和抑制其生长的可能机制,为Ａｓ２Ｏ３ 在临床上的应用提供理论依据。方法　采用免疫沉淀、Ｗｅｓｔｅｒｎ ｂｌｏｔ、生物化学及免疫荧光等方法研究了Ａｓ２Ｏ３对ＢＣＲ／ＡＢＬ蛋白酪氨酸磷酸化及其所介导的信号途径和某些凋亡相关蛋白表达的影响。结果　１μｍｏｌ／ＬＡｓ２Ｏ３ 使细胞内多种蛋白酪氨酸磷酸化减少,而且ＢＣＲ／ＡＢＬ蛋白自身酪氨酸磷酸化亦减少,但０ ．１ μｍｏｌ／ＬＡｓ２Ｏ３ 对蛋白酪氨酸磷酸化的影响不明显;Ａｓ２Ｏ３ 对蛋白酪氨酸磷酸酶（ＰＴＰ） 活性未见明显影响;Ａｓ２Ｏ３ 下调ＪＡＫ２ 蛋白的表达,但对ＳＴＡＴ１ 和ＳＴＡＴ２ 蛋白的表达以及ＳＴＡＴ１ 蛋白酪氨酸磷酸化无影响;Ａｓ２Ｏ３ 亦不影响凋亡相关蛋白Ｂｃｌ２、ＢｃｌｘＬ／Ｓ、Ｂａｘ、ＩＣＨ１Ｌ、ｐ５３、ＰＡＲＰ的表达,Ａｓ２Ｏ３ 亦使Ｋ５６２ 细胞的ＰＭＬ蛋白降解。结论　Ａｓ２Ｏ３ 可能通过减少细胞内某些蛋白,尤其是ＢＣＲ／ＡＢＬ蛋白酪氨酸磷酸化和（ 或）下调ＪＡＫ２ 蛋白的表达而干扰ＢＣＲ／ＡＢＬ致癌信号的传导,引起Ｋ５６２ 细胞凋亡和抑制其生长。     

Activation of extracellular-regulated kinase by 5-hydroxytryptamine(2A) receptors in PC12 cells is protein kinase C-independent and requires calmodulin and tyrosine kinases

5-Hydroxytryptamine (5-HT)(2A) receptors have been implicated to play a role in both the treatment and pathophysiology of a number of psychiatric disorders. Therefore, the coupling of this receptor to signals, such as extracellular signal-regulated kinase (ERK), that elicit long-term neuronal changes may be relevant. In the present study we examined the coupling of the G(q)-coupled receptor to ERK in PC12 cells, a cell line commonly used as a neuronal model system. Activation of ERK occurred through a pathway different than the protein kinase C-dependent pathways described previously in studies of non-neuronal cells. Activation of ERK, in PC12 cells, was inhibited by both chelation of extracellular Ca(2+) and by depletion of intracellular Ca(2+) stores. Surprisingly, activation was not inhibited, but actually potentiated, by a variety of protein kinase C inhibitors covering all known protein kinase C isoforms. In contrast, the coupling of receptor to activation of ERK was found to be sensitive to N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W7) and N-(4-aminobutyl)-5-chloro-1-naphthalenesulfonamide (W13), inhibitors of calmodulin, but not to 1-(N,O-bis[5-isoquinolinesulfonyl]-N-methyl-L-tyrosyl)-4-phenylpiperazine (KN62) and 2-[N-(2-hydroxyethyl)]-N-4-methoxybenzenesulfonyl)]amino-N-(4-chlorocinnamyl)-N-methylbenzylamine) (KN93), inhibitors of calmodulin-dependent protein kinase. Additionally, the general tyrosine kinase inhibitor genistein, as well as the Src inhibitor PP1 and the epidermal growth factor receptor kinase inhibitor 4-(3-chloroanilino)-6,7-dimethoxyquinazoline (AG 1478), inhibited receptor-mediated activation of ERK, suggesting a role for tyrosine kinases. In fact, 5-HT was found to stimulate tyrosine phosphorylation of a number of proteins, and this phosphorylation was inhibited by W7. 5-HT(2A) receptor-activation of ERK through a protein kinase C-independent pathway requiring Ca(2+)/calmodulin/tyrosine kinases represents a pathway distinct from those described in studies of non-neuronal cells.     

Alpha-melanocyte stimulating hormone protects against H2O2-induced inhibition of wound restitution in IEC-6 cells via a Syk kinase- and NF-kappabeta-dependent mechanism

Epithelial injury and repair are central consequences of ischemia and reperfusion of the gut. Intestinal mucosal wounds are repaired in part by epithelial restitution. However, the signaling mechanisms regulating restitution remain poorly understood, and few therapies to enhance restitution have been described. Previously we demonstrated that alpha-melanocyte-stimulating hormone (alpha-MSH) protected against postischemic gut injury in the rat. In this report, we tested the effects and mechanisms of alpha-MSH on wound restitution of rat small intestine (IEC-6) cells subjected to H2O2 stress with or without scrape wounding. H2O2 treatment resulted in tyrosine phosphorylation of Syk kinase and its downstream target IkappaBalpha, with subsequent NF-kappaB activation. Alpha-MSH and the Syk kinase inhibitor piceatannol blocked these processes. In scrape-wounded cells, H2O2 inhibited wound restitution, and this was partially restored by cotreatment with alpha-MSH or piceatannol. In contrast, overexpression of NF-kappaB p65 or Syk kinase, but not a dominant-negative mutant of Syk kinase, aggravated H2O2 inhibition of wound restitution, and inhibitors of c-Src tyrosine kinase or phosphatidylinositol-3 kinase were without effect. The results indicate an important role for Syk tyrosine kinase and the NF-kappaB pathway in the response to oxidant stress and the impairment of epithelial restitution in IEC-6 cells. The data also disclose that the beneficial effects of alpha-MSH on gut ischemia/reperfusion injury may relate to its acceleration of epithelial restitution.     

Histamine H3-receptor-induced attenuation of norepinephrine exocytosis: a decreased protein kinase a activity mediates a reduction in intracellular calcium

We had reported that activation of presynaptic histamine H(3)-receptors inhibits norepinephrine exocytosis from depolarized cardiac sympathetic nerve endings, an action associated with a marked decrease in intraneuronal Ca(2+) that we ascribed to a decreased Ca(2+) influx. An H(3)-receptor-mediated inhibition of cAMP-dependent phosphorylation of Ca(2+) channels could cause a sequential attenuation of Ca(2+) influx, intraneuronal Ca(2+) and norepinephrine exocytosis. We tested this hypothesis in sympathetic nerve endings (cardiac synaptosomes) expressing native H(3)-receptors and in human neuroblastoma SH-SY5Y cells transfected with H(3)-receptors. Norepinephrine exocytosis was elicited by K(+) or by stimulation of adenylyl cyclase with forskolin. H(3)-receptor activation markedly attenuated the K(+)- and forskolin-induced norepinephrine exocytosis; pretreatment with pertussis toxin prevented this effect. Similar to forskolin, 8-bromo-cAMP elicited norepinephrine exocytosis but, unlike forskolin, it was unaffected by H(3)-receptor activation, demonstrating that inhibition of adenylyl cyclase is a pivotal step in the H(3)-receptor transductional cascade. Indeed, we found that H(3)-receptor activation attenuated norepinephrine exocytosis concomitantly with a decrease in intracellular cAMP and PKA activity in SH-SY5Y-H(3) cells. Moreover, pharmacological PKA inhibition acted synergistically with H(3)-receptor activation to reduce K(+)-induced peak intracellular Ca(2+) in SH-SY5Y-H(3) cells and norepinephrine exocytosis in cardiac synaptosomes. Furthermore, H(3)-receptor activation synergized with N- and L-type Ca(2+) channel blockers to reduce norepinephrine exocytosis in cardiac synaptosomes. Our findings suggest that the H(3)-receptor-mediated inhibition of norepinephrine exocytosis from cardiac sympathetic nerves results sequentially from H(3)-receptor-G(i)/G(o) coupling, inhibition of adenylyl cyclase activity, and decreased cAMP formation, leading to diminished PKA activity, and thus, decreased Ca(2+) influx through voltage-operated Ca(2+) channels.     

Impaired development of V gamma 3 dendritic epidermal T cells in p56lck protein tyrosine kinase-deficient and CD45 protein tyrosine phosphatase- deficient mice

To determine whether p56lck protein tyrosine kinase and CD45 protein tyrosine phosphatase are involved in the signal transduction during intrathymic differentiation of gamma/delta T cells, we have examined the development of T cells expressing V gamma 3 T cell receptor (TCR) in mice deficient for either protein. The skin from both mice contained significantly reduced numbers of dendritic epidermal T cells expressing decreased levels of V gamma 3 TCR at the cell surface. Analysis of the fetal thymus from these mice suggested that maturation of V gamma 3 thymocytes was blocked at the immature stage that was characterized by the low level of V gamma 3 TCR and the high level of heat stable antigen. These results imply that both p56lck and CD45 are involved in the signal transduction during maturation of V gamma 3 T cells in the fetal thymus.