Inhibitory effect of D1-like and D3 dopamine receptors on norepinephrine-induced proliferation in vascular smooth muscle cells

The sympathetic nervous system plays an important role in the regulation of blood pressure. There is increasing evidence for positive and negative interactions between dopamine and adrenergic receptors; the activation of the alpha-adrenergic receptor induces vasoconstriction, whereas the activation of dopamine receptor induces vasorelaxation. We hypothesize that the D1-like receptor and/or D3 receptor also inhibit alpha1-adrenergic receptor-mediated proliferation in vascular smooth muscle cells (VSMCs). In this study, VSMC proliferation was determined by measuring [3H]thymidine incorporation, cell number, and uptake of 3-(4,5-dimethylthiazol-2-yl)-diphenyltetrazolium bromide (MTT). Norepinephrine increased VSMC number and MTT uptake, as well as [3H]thymidine incorporation via the alpha1-adrenergic receptor in aortic VSMCs from Sprague-Dawley rats. The proliferative effects of norepinephrine were attenuated by the activation of D1-like receptors or D3 receptors, although a D1-like receptor agonist, fenoldopam, and a D3 receptor agonist, PD-128907, by themselves, at low concentrations, had no effect on VSMC proliferation. Simultaneous stimulation of both D1-like and D3 receptors had an additive inhibitory effect. The inhibitory effect of D3 receptor was via protein kinase A, whereas the D1-like receptor effect was via protein kinase C-zeta. The interaction between alpha1-adrenergic and dopamine receptors, especially D1-like and D3 receptors in VSMCs, could be involved in the pathogenesis of hypertension.     

Photoaffinity labeling of dopamine D1 receptors

A high-affinity radioiodinated D1 receptor photoaffinity probe, (+/-)-7-[125I]iodo-8-hydroxy-3-methyl-1-(4-azidophenyl)-2,3,4,5-tetra hyd ro- 1H-3-benzazepine ([125I]IMAB), has been synthesized and characterized. In the absence of light, [125I]IMAB bound in a saturable and reversible manner to sites in canine brain striatal membranes with high affinity (KD approximately equal to 220 pM). The binding of [125I]IMAB was stereoselectively and competitively inhibited by dopaminergic agonists and antagonists with an appropriate pharmacological specificity for D1 receptors. The ligand binding subunit of the dopamine D1 receptor was visualized by autoradiography following photoaffinity labeling with [125I]IMAB and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Upon photolysis, [125I]IMAB incorporated into a protein of apparent agents in a stereoselective manner with a potency order typical of dopamine D1 receptors. In addition, smaller subunits of apparent Mr 62,000 and 51,000 were also specifically labeled by [125I]IMAB in these species. Photoaffinity labeling in the absence or presence of multiple protease inhibitors did not alter the migration pattern of [125I]IMAB-labeled subunits upon denaturing electrophoresis in both the absence or presence of urea or thiol reducing/oxidizing reagents. [125I]IMAB should prove to be a useful tool for the subsequent molecular characterization of the D1 receptor from various sources and under differing pathophysiological states.     

Pharmacological characterization of mammalian D1 and D2 dopamine receptors expressed in Drosophila Schneider-2 cells

Mammalian D1 and D2 dopamine receptors were stably expressed in Drosophila Schneider-2 (S2) cells and screened for their pharmacological properties. Saturable, dose-dependent, high affinity binding of the D1-selective antagonist [3H]SCH-23390 was detected only in membranes from S2 cells induced to express rat dopamine D1 receptors, while saturable, dose-dependent, high affinity binding of the D2-selective antagonist [3H]methylspiperone was detected only in membranes from S2 cells induced to express rat dopamine D2 receptors. No specific binding of either radioligand could be detected in membranes isolated from uninduced or untransfected S2 cells. Both dopamine D1 and D2 receptor subtypes displayed the appropriate stereoselective binding of enantiomers of the nonselective antagonist butaclamol. Each receptor subtype also displayed the appropriate agonist stereoselectivities. The dopamine D1 receptor bound the (+)-enantiomer of the D1-selective agonist SKF38393 with higher affinity than the (-)-enantiomer, while the dopamine D2 receptor bound the (-)-enantiomer of the D2-selective agonist norpropylapomorphine with higher affinity than the (+)-enantiomer. At both receptor subtypes, dopamine binding was best characterized as occurring to a single low affinity site. In addition, the low affinity dopamine binding was also found to be insensitive to GTPgammaS and magnesium ions. Overall, the pharmacological profiles of mammalian dopamine D1 and D2 receptors expressed in Drosophila S2 cells is comparable to those observed for these same receptors when they are expressed in mammalian cell lines. A notable distinction is that there is no evidence for the coupling of insect G proteins to mammalian dopamine receptors. These results suggest that the S2 cell insect G system may provide a convenient source of pharmacologically active mammalian D1 and D2 dopamine receptors free of promiscuous G protein contaminants.     

The role of D1 and D2 dopamine receptors of the rat nucleus accumbens in immunostimulation

The analysis of the immune response changes in Wistar rats has shown that bilateral electrolytic lesions of the nucleus accumbens characterized by a high density of D1 an D2 dopamine (DA) receptors resulted in a decrease of the immune response to SRBC. Administration of selective agonists of D1 and D2 DA receptors to sham-operated animal: 20 mg/kg of SKF 38393 or 1.0 mg/kg of quinpirol, respectively, produced significant enhancement of plaque- and rosette-formation. However, the immune response level in the damaged rats did not increase following quinpirol administration, but was maintained at control values, rather. At the same time, activation of D1 DA receptors in rats with destructed nucleus accumbens did not affect the immune response level as compared to that of sham-operated animals receiving SKF 38393. The data obtained give evidence of involvement of D2 DA receptors of the nucleus accumbens in immunomodulation, although D2 DA receptors of other brain structures may also contribute to this process. D1 DA receptors of this localization seem not to play any important role in the immune response control.     

Differential contribution of dopamine D1 and D2 receptors in the mu-opioidergic immunomodulation

The study has shown that activation of mu-opioid receptors by a highly selective agonist DAGO (100 microg/kg) results in a significant increase of the immune response to antigen (SRBC, 5% 10(8)) in CBA mice. Haloperidol (2 mg/kg), a selective antagonist of the postsynaptic dopamine (DA) receptors, prevented immunostimulating effect of DAGO. In contrast, selective D1--antagonist SCH 23390 (1 mg/kg) did not affect on DAGO-induced enhancing of immune reactivity. At the same time, the blockade of both types of DA receptors (D1 and D2) caused similar immunosuppressing effects. These data suggest a possible differential role for D1 and D2 receptors in mu-opioidergic immunomodulation.     

盐酸罗哌卡因对骨肉瘤细胞增殖、侵袭、凋亡的影响及其机制*

目的:探讨盐酸罗哌卡因对骨肉瘤细胞增殖、侵袭、凋亡的影响及分子机制。方法:采用逐步增加药物剂量诱导法建立骨肉瘤多柔比星耐药细胞株(U2OS/DOX),用浓度分别为0、20、50、100 μg/ml的盐酸罗哌卡因处理U2OS/DOX细胞,作为不同浓度盐酸罗哌卡因处理组;将pcDNA3.1、pcDNA3.1-Livin转染至U2OS/DOX细胞中再用浓度为100 μg/ml的盐酸罗哌卡因处理,记为盐酸罗哌卡因100 μg/ml+pcDNA3.1组、盐酸罗哌卡因100 μg/ml+pcDNA3.1-Livin组。MTT检测细胞增殖抑制率及细胞半数抑制浓度(IC₅₀);蛋白质印迹(Western blot)法检测细胞周期蛋白依赖性激酶抑制剂1A(P21)、活化的半胱氨酸天冬氨酸蛋白酶-3(Cleaved Caspase-3)、上皮钙黏蛋白(E-cadherin)、基质金属蛋白酶2(MMP-2)、Livin蛋白表达;克隆形成实验检测细胞克隆形成数;流式细胞术检测细胞凋亡;Transwell检测细胞迁移和侵袭;实时荧光定量PCR(RT-qPCR)检测Livin mRNA表达水平。结果:多柔比星浓度大于1 μg/ml时,骨肉瘤细胞U2OS增殖抑制率显著升高,且具有剂量依赖性(P＜0.05);多柔比星浓度大于10 μg/ml时,骨肉瘤细胞骨肉瘤耐药细胞U2OS/DOX增殖抑制率显著升高,且具有剂量依赖性(P＜0.05)。盐酸罗哌卡因处理的U2OS/DOX细胞中P21、Caspase-3、E-cadherin表达水平显著升高,MMP-2表达水平显著降低,细胞增殖抑制率显著升高,克隆形成数显著降低,细胞凋亡率显著升高,细胞迁移、侵袭数显著降低,Livin表达水平显著降低,且呈浓度依赖性(P＜0.05)。过表达Livin部分逆转了盐酸罗哌卡因对细胞U2OS/DOX增殖、迁移、侵袭的抑制作用及凋亡的促进作用。结论:盐酸罗哌卡因能明显抑制对多柔比星具有耐药性的骨肉瘤细胞的增殖,迁移和侵袭,明显促进骨瘤细胞凋亡,其机制可能与Livin有关。     

Identification of D1-like dopamine receptors on human blood platelets

Dopamine is able to inhibit the epinephrine-induced aggregation of human blood platelets, but the mechanism of action has not been elucidated. In this study we report that membranes from human blood platelets possess high affinity, saturable and stereoselective binding sites for the D1 dopamine receptor antagonist (3H) SCH 23390. (3H) SCH 23390 appeared to label a single class of binding sites with a Bmax of 18.6 +/- 1.6 fmol/mg protein and a KD of 0.8 nM. The potencies of different dopaminergic antagonists and agonists in displacing (3H) SCH 23390 from blood platelet membranes were similar to those obtained for striatal membranes. Unlike the classically defined D1 receptors, e.g. those in striatum, the D1 receptor sites on platelets appeared not to be coupled to the adenylate cyclase system, hence the term "D1-like". The D1 agonist SKF 38393 was more potent than dopamine in inhibiting platelet aggregation induced by epinephrine, and the effects of dopamine and SKF 38393 were prevented by SCH 23390. These results suggest that the inhibitory action of dopamine on the epinephrine-induced platelet aggregation is mediated through these D1-like receptors.     

The distribution of dopamine D1 and D2 receptors in the brain of rodents and carnivores]

Studies have been made on the density of receptors and dissociation constants for dopamine D1- and D2-receptors in the striatum, n. accumbens with the olfactory tubercles and in the frontal cortex of Wistar rats, Norway rats and silver foxes. D1 binding was found to be significantly higher than D2 one in all the analysed brain structures of the animals studied, especially in the striatum. Although the analysis of D1- and D2-receptor binding kinetics revealed differences in Wistar and Norway rats, more significant differences were found between rats and silver foxes.     

Amphioxus expresses both vertebrate-type and invertebrate-type dopamine D1 receptors

The cephalochordate amphioxus (Branchiostoma floridae) has recently been placed as the most basal of all the chordates, which makes it an ideal organism for studying the molecular basis of the evolutionary transition from invertebrates to vertebrates. The biogenic amine, dopamine regulates many aspects of motor control in both vertebrates and invertebrates, and in both cases, its receptors can be divided into two main groups (D1 and D2) based on sequence similarity, ligand affinity and effector coupling. A bioinformatic study shows that amphioxus has at least three dopamine D1-like receptor sequences. We have recently characterized one of these receptors, AmphiD1/β, which was found to have high levels of sequence similarity to both vertebrate D1 receptors and to β-adrenergic receptors, but functionally appeared to be a vertebrate-type dopamine D₁ receptor. Here, we report on the cloning of two further dopamine D₁ receptors (AmphiAmR1 and AmphiAmR2) from adult amphioxus cDNA libraries and their pharmacological characterisation subsequent to their expression in cell lines. AmphiAmR1 shows closer structural similarities to vertebrate D₁-like receptors but shows some pharmacological similarities to invertebrate “DOP1” dopamine D₁-like receptors. In contrast, AmphiAmR2 shows closer structural and pharmacological similarities to invertebrate “INDR”-like dopamine D₁-like receptors.     

Coupling of D1 and D5 dopamine receptors to multiple G proteins

Dopamine receptors are a subclass of the super family of G protein-coupled receptors, that transduce their effects by coupling to specific G proteins. Within the dopamine receptor family, the adenylyl cyclase stimulatory receptors include the D₁ and D₅ subtypes. The D₁ and D₅ dopamine receptors are genetically distinct, sharing >80% sequence homology within the highly conserved seven transmembrane spanning domains, but displaying only 50% overall homology at the amino acid level. When expressed in transfected GH₄C₁ rat pituitary cells, both D₁ and D₅ receptors stimulate adenylyl cyclase and have identical affinities toward dopaminergic agonists and antagonists. In order to analyze specific signaling pathways mediated by activation of either D₁ or D₅ receptors, we have identified the G proteins that are coupled to these receptors. Through functional analyses and competition binding studies, and from immunoprecipitation techniques, using antisera against the various α subunits of G proteins, we have established that both D₁ and D₅ receptors couple to G_sα. In addition, D₁ receptors are also coupled to G_oα. Since G_oα has been implicated in the regulation of Ca²⁺, K⁺, and Na⁺ channels, this finding would suggest that D₁ receptors can mediate the functional activity of these ion channels. There is also evidence to indicate that D₅ receptors couple to G_zα, a novel G protein abundantly expressed in neurons. Thus, despite similar pharmacological properties, such differential coupling of D₁ and D₅ receptors to G proteins other than G_sα, indicates that dopamine can transduce varied signaling responses upon the simultaneous stimulation of both these receptors.     

Irreversible interaction of beta-haloalkylamine derivatives with dopamine D1 and D2 receptors

The interaction of beta-haloalkylamine derivatives of dopamine agonists and antagonists with 3H-spiperone binding (D2 sites) and 3H-flupenthixol binding (D1 sites) was studied. N-chloroethyl derivatives of phenothiazines and thioxanthenes were potent inhibitors of the binding of both ligands. The in vitro inhibition of binding produced by these compounds was irreversible. The drugs were however only weakly active in vivo. The results suggest that beta-haloalkylamine derivatives of neuroleptics may be useful compounds for studying dopamine receptors in vitro.     

Reduced D2-mediated signaling activity and trans-synaptic upregulation of D1 and D2 dopamine receptors in mice overexpressing the dopamine transporter

The dopamine transporter (DAT) regulates the temporal and spatial actions of dopamine by reuptaking this neurotransmitter into the presynaptic neurons. We recently generated transgenic mice overexpressing DAT (DAT-tg) that have a 3-fold increase in DAT protein levels which results in a 40% reduction of the extracellular DA concentration in the striatum. The aim of this study was to examine the effect of this reduction in dopaminergic tone on postsynaptic responses mediated by dopamine receptors. We report here that DAT-tg mice have increased levels of striatal D1 (30%) and D2 (approximately 60%) dopamine receptors with D1 receptor signaling components not significantly altered, as evidenced by unaffected basal or stimulated levels of phospho-GluR1 (Ser845) and phospho-ERK2. However, the novel D2 mediated Akt signaling is markedly altered in DAT-tg animals. In particular, there is a 300% increase in the basal levels of phospho-Akt in the striatum of DAT-tg, reflecting the reduced extracellular dopamine tone in these animals. This increase in basal pAkt levels can be pharmacologically recapitulated by partial dopamine depletion in WT mice treated with the selective tyrosine hydroxylase inhibitor alpha-methyl-para-tyrosine (alpha-MPT). Behaviorally, DAT-tg animals demonstrate an augmented synergistic interaction between up-regulated D1 and D2 receptors, which results in increased climbing behavior in transgenic mice after stimulation with either apomorphine or a co-administration of selective D1 and D2 receptor agonists. In sum, our study reveals that hypodopaminegia caused by up-regulation of DAT results in significant alterations at postsynaptic receptor function with most notable dysregulation at the level of D2 receptor signaling.     

The role of prefrontal dopamine D1 receptors in the neural mechanisms of associative learning

Dopamine is thought to play a major role in learning. However, while dopamine D1 receptors (D1Rs) in the prefrontal cortex (PFC) have been shown to modulate working memory-related neural activity, their role in the cellular basis of learning is unknown. We recorded activity from multiple electrodes while injecting the D1R antagonist SCH23390 in the lateral PFC as monkeys learned visuomotor associations. Blocking D1Rs impaired learning of novel associations and decreased cognitive flexibility but spared performance of already familiar associations. This suggests a greater role for prefrontal D1Rs in learning new, rather than performing familiar, associations. There was a corresponding greater decrease in neural selectivity and increase in alpha and beta oscillations in local field potentials for novel than for familiar associations. Our results suggest that weak stimulation of D1Rs observed in aging and psychiatric disorders may impair learning and PFC function by reducing neural selectivity and exacerbating neural oscillations associated with inattention and cognitive deficits.     

Comparative biochemical pharmacology of central nervous system dopamine D1 and D2 receptors

The biochemical properties of central nervous system (CNS) dopamine (DA) D1 and D2 receptors were examined using the specific antagonists [3H]SCH23390 and [3H]raclopride, respectively. There is a different participation of sulfhydryl (-SH) and disulfide (-SS-) groups in the binding site and/or coupling to second messenger systems of D1 and D2 receptors. The ionic studies with [3H]SCH23390 showed slight agonist and antagonist affinity shifts for the D1 receptor. On the other hand, the D2 receptor is very sensitive to cations; even if lithium and sodium influence specific [3H]raclopride binding in a similar manner, there appear to be quantitative differences between these two ions that cannot be explained by surface charge mechanisms. The distribution of D1 and D2 receptors was heterogenous in both species, with the greatest densities in the neostriatum, where the highest concentrations of DA and metabolites were measured. Regions with low endogenous DA content (cerebral cortex and hippocampus) had lower densities of DA receptors. Furthermore, these binding sites were differentially localized within the various regions, and there were substantially more D1 than D2 receptors. The functional significance and heterogeneities in the distribution of D1 and D2 receptors can be related to dopaminergic innervation and turnover.     

Fluorescence studies reveal heterodimerization of dopamine D1 and D2 receptors in the plasma membrane

Evidence for hetero-oligomerization has recently been provided for various G protein-coupled receptors. In this paper, we have studied the possibility that dopamine D(1) and D(2) receptors physically interact with each other. Human dopamine D(1) and D(2) receptors were fluorescently tagged with derivatives of green fluorescence protein and transiently coexpressed in the membrane of human embryonic kidney 293 cells. Using qualitative fluorescence spectroscopy, as well as quantitative F?rster resonance energy transfer (FRET) analysis, performed in a single cell by confocal microscopy and fluorescence lifetime microscopy, we show that dopamine D(1) and D(2) receptors can form hetero-oligomers in the plasma membrane. The degree of receptor protein-protein interaction is significantly enhanced by concomitant addition of D(1) and D(2) receptor subtype-specific agonists. Our investigations extend biochemical and electrophysiological studies and give insights into the regulation and synergistic mode of operation of dopamine receptors.     

Molecular cloning and characterization of crustacean type-one dopamine receptors: D1alphaPan and D1betaPan

Dopamine (DA) differentially modulates identified neurons in the crustacean stomatogastric nervous system (STNS). While the electrophysiological actions of DA have been well characterized, little is known about the dopaminergic transduction cascades operating in this system. As a first step toward illuminating the molecular underpinnings of dopaminergic signal transduction in the crustacean STNS, we have cloned and characterized two type-one DA receptors (DARs) from the spiny lobster (Panulirus interruptus): D(1alphaPan) and D(1betaPan). We found that the structure and function of these arthropod DARs are well conserved across species. Using a heterologous expression system, we determined that DA, but not serotonin, octopamine, tyramine or histamine activates these receptors. When stably expressed in HEK cells, the D(1alphaPan) receptor couples with Gs, and DA elicits an increase in [cAMP]. The D(1betaPan) receptor responds to DA with a net increase in [cAMP] that is mediated by Gs and Gz.     

Stable expression of human D3 dopamine receptors in GH4C1 pituitary cells.

Human D3 dopamine receptor DNA was stably transfected into GH4C1 pituitary cells. Displacement of iodosulpiride binding in hD3 transfected cells (Kd = 0.3 nM, Bmax = 89 fmol/mg protein) by dopaminergic ligands was indistinguishable from that of hD3 receptors in CHO cells. Only two clonal cell lines exhibited weak GppNHp-dependent shifts in [3H]N-0437 binding, and these were used for functional assays. Neither arachidonic acid metabolism, cAMP levels, inositol phosphate turnover, intracellular calcium, or potassium currents were consistently affected by dopamine (1-10 microM). The paucity of responses indicates that human D3 receptors do not couple efficiently to these second messengers in GH4C1 cells.     

Pergolide: a dopamine agonist at both D1 and D2 receptors.

Pergolide is a potent, direct-acting dopamine agonist used in treating Parkinson's disease. It is an agonist found recently to have high affinity for D3 receptors. The affinity of pergolide for D1 receptors is lower than for D2 receptors, and there have been some reports that it may not interact with D1 receptors in vivo at doses used to activate D2 receptors. A growing body of evidence suggests that pergolide does occupy and activate D1 receptors in vivo, although the relevance to therapeutic efficacy in Parkinson's disease needs further study.