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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The 5-hydroxytryptamine1A (5-HT1A) receptor can bind certain beta-adrenergic receptor antagonists, such as pindolol, with high affinity. Such pharmacological cross-reactivity suggests a structural similarity in the ligand binding site between the two receptors. To identify this structural entity, we mutated Asn385 in the seventh transmembrane domain of the human 5-HT1A receptor, based on the observation that this residue is conserved in all 5-HT1A and beta-adrenergic receptors of different species but is absent in all other cloned guanine nucleotide-binding protein-coupled receptors. This single point mutation (Asn385 to valine) causes a highly selective decrease in the affinity of pindolol and other aryloxyalkylamines for the mutant receptor (about 100-fold), while producing only minor changes in the binding of other 5-HT agonists and antagonists. The results provide direct evidence that Asn385 is responsible for the high affinity interaction between 5-HT1A receptors and aryloxyalkylamine beta-adrenergic antagonists but is not required for the binding of other chemical classes of ligands.
Mol Pharmacol 1992 Apr
PMID:Identification of a single amino acid residue responsible for the binding of a class of beta-adrenergic receptor antagonists to 5-hydroxytryptamine1A receptors. 134 54

Previous studies have demonstrated the existence of a large receptor reserve for agonists at somatodendritic 5-hydroxytryptamine1A (5-HT1A) serotonin receptors in the raphe nuclei of the rat. 5-HT1A agonists with anxiolytic properties (e.g., buspirone, gepirone, and ipsapirone) display full intrinsic activity at these receptors but are partial agonists at postsynaptic 5-HT1A receptors, which suggests that the latter sites may be devoid of a receptor reserve. In the present studies, this was directly determined by examining the relationship between receptor occupancy and response at postsynaptic 5-HT1A receptors, in rat hippocampus, mediating the inhibition of forskolin-stimulated adenylyl cyclase activity, using the method of partial irreversible receptor inactivation. Rats were treated with vehicle or the irreversible antagonist N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), and 24 hr later hippocampi were removed for saturation analysis of [3H]8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) binding to 5-HT1A receptors or for adenylyl cyclase assays. EEDQ (1 and 6 mg/kg) dose-dependently reduced the maximal number of [3H]8-OH-DPAT binding sites by 68.5 and 80%, respectively, without altering the Kd. Concentration-response curves were generated for inhibition of forskolin-stimulated adenylyl cyclase activity by 5-HT and the selective 5-HT1A agonist N,N-dipropyl-5-carboxamidotryptamine (DP-5-CT). EEDQ treatment dose-dependently reduced the maximal inhibitory effect of 5-HT [percentage of inhibition: control, 23.6; EEDQ (1 mg/kg), 13.4; EEDQ (6 mg/kg), 8.9], without altering either the slope factor (1.01) or the EC50 (96.4 nM). Analogous results were obtained with DP-5-CT [percentage of maximal inhibition: control, 24.1; EEDQ (1 mg/kg), 15.2; EEDQ (6 mg/kg), 10.7), again without changes in slope factor (0.89) or EC50 (9.9 nM). Analysis of double-reciprocal plots of equieffective concentrations of agonist, followed by calculation of fractional receptor occupancy, revealed a linear relationship between receptor occupancy and response for both 5-HT and DP-5-CT (i.e., an absence of receptor reserve). The receptor specificity of the effect of EEDQ was demonstrated in two ways. First, it was shown that pretreatment of rats with the selective 5-HT1A partial agonist BMY 7378 (10 mg/kg) before EEDQ afforded substantial protection (about 75%) against loss of the inhibitory effect of DP-5-CT on forskolin-stimulated adenylyl cyclase activity. Second, EEDQ did not alter the inhibition of forskolin-stimulated adenylyl cyclase activity induced by the adenosine A1 receptor agonist phenylisopropyladenosine (PIA).(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Pharmacol 1992 Jun
PMID:Lack of apparent receptor reserve at postsynaptic 5-hydroxytryptamine1A receptors negatively coupled to adenylyl cyclase activity in rat hippocampal membranes. 135 34

5-Hydroxytryptamine (5HT)1C and 5HT2 receptors appear to be closely related, from a molecular viewpoint, displaying similar second messenger systems and a high degree of sequence homology. However, there are striking differences in the interactions of 5HT with 5HT1C and 5HT2 receptors; 5HT is generally more potent in stimulating responses mediated through 5HT1C receptors than responses mediated through 5HT2 receptors. Also [3H]5HT labels 5HT1C receptors and not 5HT2 receptors. In order to explore more fully the molecular rationale for these differences, radioligand binding studies were performed in rat, human, and porcine brain and choroid plexus tissues and in mammalian cells transfected with rat 5HT1C or 5HT2 receptors; second messenger studies (inositol phosphate accumulation) were performed in the transfected cells. The second messenger studies confirmed the approximately 10-fold higher potency of 5HT in stimulating intracellular responses through 5HT1C receptors (EC50 = 8.3 nM) than in stimulating intracellular responses through 5HT2 receptors (EC50 = 101 nM). An agonist radioligand selective for the 5HT1C and 5HT2 receptors, 2,5-dimethoxy-(4-[125I]iodo)phenylisopropylamine, was used, as well as [3H]5HT, [3H]mesulergine (antagonist radioligand for 5HT1C receptors), and [3H]ketanserin (antagonist radioligand for 5HT2 receptors). Computer-assisted analyses of the binding data revealed two agonist affinity states for the 5HT1C receptor. The agonist high affinity state of the receptor was modifiable by guanyl nucleotides. The proportion of agonist high affinity states, relative to the total receptor population, was approximately 10% for both receptors. The apparent higher affinity of 5HT for the radiolabeled 5HT1C receptors was due to the higher affinity 5HT displayed for the agonist low affinity state of the 5HT1C receptor, compared with the affinity of 5HT for the agonist low affinity state of the 5HT2 receptor. The correspondence between the higher affinity of 5HT for the agonist low affinity state of the 5HT1C receptor, relative to the 5HT2 receptor, and the higher potency of 5HT in stimulating 5HT1C responses indicates that 5HT interacts with the agonist low affinity state of the 5HT1C and 5HT2 receptors in initiating its biological effects. These observations indicate that guanine nucleotide-binding protein (G protein)-coupled receptors can exhibit high affinity for neurotransmitters in both the free receptor and the G protein-coupled states and that receptors exhibiting this property may represent a novel subfamily of G protein-coupled receptors.
Mol Pharmacol 1992 Aug
PMID:Molecular pharmacological differences in the interaction of serotonin with 5-hydroxytryptamine1C and 5-hydroxytryptamine2 receptors. 135 62

C6 rat glioma cells were utilized as a model system to probe the 'serotonin/norepinephrine link' at the level of preproenkephalin (PPE) gene expression. The beta adrenoceptor mediated increase in PPE mRNA was attenuated by the selective beta 1 adrenoceptor antagonist metoprolol which blocked the isoproterenol induced cyclic AMP generation by 97%. The subtype nonspecific antagonist propranolol blocked both the isoproterenol induced increase in cyclic AMP and the increase in the PPE mRNA steady-state levels. Serotonin (5-HT) had no effect on the density of beta adrenoceptors or their down-regulation by isoproterenol and did not alter the PPE gene expression in the absence of the beta signal. However, 5-HT significantly deamplified the beta signal mediated enhancement of the PPE mRNA thus indicating that the aminergic link occurs beyond the beta adrenoceptor.
Brain Res Mol Brain Res 1992 Dec
PMID:The 'serotonin/norepinephrine link' beyond the beta adrenoceptor. 136 25

The control of aldosterone secretion in vivo by serotonin was studied in conscious rats. Serial blood samples were taken from indwelling arterial cannulae before and after i.p. administration of 1 ml (4 g/l) 5-hydroxytryptophan (5-HTP), the precursor of serotonin (5-HT), or saline, and analysed for 5-HTP, serotonin, 5-hydroxyindoleacetic acid, plasma renin activity (PRA), corticosterone, aldosterone, sodium and potassium concentration. The relative contribution of the hypothalamo-pituitary adrenal axis was investigated in animals pretreated with the synthetic glucocorticoid dexamethasone. 5-HTP caused a significant increase in all parameters within 45 min except for plasma sodium and potassium. Saline administration showed no significant effect. Dexamethasone pretreatment significantly impaired the corticosterone and aldosterone response to 5-HTP, although the aldosterone response was merely attenuated. No other parameter was affected by dexamethasone pretreatment. The results show that administration of 5-HTP, which increases serum serotonin levels, stimulates PRA, corticosterone and aldosterone secretion. Dexamethasone pretreatment inhibits the aldosterone response, though not completely, suggesting that the stimulatory action of 5-HTP involves the release of ACTH, which stimulates corticosterone and aldosterone secretion by the adrenal cortex. The failure of dexamethasone to block the aldosterone response completely, suggests the involvement of other mechanisms such as the renin-angiotensin system or a direct action of serotonin on the adrenal zona glomerulosa.
J Steroid Biochem Mol Biol 1992 Mar
PMID:Serotoninergic stimulation of aldosterone secretion in vivo: role of the hypothalamo-pituitary adrenal axis. 137 72

Poly(A)+ mRNAs from the cerebral cortex of aged (24 months) and young adult (3 months) rats were isolated and injected into Xenopus oocytes to express functional neurotransmitter receptors and voltage-operated channels. Electrophysiological recordings of induced membrane currents were used as a measure of the relative amounts of mRNA encoding different receptors and channels, and to study their functional properties. There were no large differences apparent between mRNAs from aged and adult rats, in marked contrast to the dramatic (1000-fold) changes in mRNA expression that occur during embryonic and postnatal development. The membrane currents induced by glutamate or acetylcholine (ACh) application were roughly one third smaller in oocytes injected with mRNA from aged cerebral cortex than in oocytes injected with mRNA from adult cerebral cortex, whereas currents induced by gamma-aminobutyric acid (GABA), kainate or serotonin (5-HT) application, and by activation of voltage-operated Na+ and Ca2+ channels were not significantly different. We did not observe any age-related differences in the properties of the receptors and channels studied.
Brain Res Mol Brain Res 1992 Mar
PMID:Messenger RNAs coding for receptors and channels in the cerebral cortex of adult and aged rats. 137 2

Serotonin [5-hydroxytryptamine (5-HT)] receptors are distinguished pharmacologically by their characteristic affinities for agonists and antagonists. Two serotonin receptors, the 5-HT2 and 5-HT1c, share a number of pharmacologic and structural properties while differing in their affinities for certain agonists and antagonists. To identify regions of the 5-HT2 and 5-HT1c receptors important for specifying their unique pharmacology, we constructed six chimeric 5-HT2/5-HT1c receptors in which domains of each receptor were exchanged. The abilities of several drugs to inhibit [3H]mesulergine bound to the chimeric and parent receptors transiently expressed in COS-7 cells were then examined. For spiperone and haloperidol (both butyrophenones), chimeras that exchanged transmembrane (TM) domains I and II or TMs I-III had the greatest effects on binding affinity. The binding affinity of cinanserin (a cinnamanilide) was significantly changed in all the chimeras studied. In contrast, the binding of ketanserin (a 4-fluorobenzoylpiperidine) was strongly influenced by chimeras that exchanged TMs I-III (but not I and II) and by chimeras that exchanged intracellular loop 3 to TM VII. 5-HT binding affinity was greatly altered for chimeras that exchanged domains of intracellular loop 3 to TM VII, with minor effects being noted for chimeras that exchanged TMs I and II and I-III. The affinities of the nonselective drugs mesulergine, mianserin, and m-chlorophenylpiperazine were relatively unaffected when domains of the 5-HT2 and 5-HT1c receptors were exchanged. Taken together, these results imply that structurally diverse 5-HT2 antagonists utilize distinct regions of the 5-HT2 receptor for high affinity binding.
Mol Pharmacol 1992 Oct
PMID:Identification of receptor domains that modify ligand binding to 5-hydroxytryptamine2 and 5-hydroxytryptamine1c serotonin receptors. 143 40

To determine whether changes in the lipid dynamics of the plasma membrane bilayer are responsible for hypoxic stimulation of serotonin (5-hydroxytryptamine [5-HT]) transport in pulmonary artery endothelial cells, we solubilized and isolated phospholipid and protein fractions from plasma membrane vesicles derived from endothelial cells exposed to 20% O2 (normoxia) or 0% O2 (hypoxia) for 24 h. Four different combinations of proteoliposomes were prepared by reconstituting (1) normoxic protein and normoxic phospholipid, (2) normoxic protein and hypoxic phospholipid, (3) hypoxic protein and normoxic phospholipid, and (4) hypoxic protein and hypoxic phospholipid. Fluorescence anisotropy of diphenylhexatriene (DPH), a measure of fluidity, and 5-HT transport were evaluated in each of the four groups of reconstituted proteoliposomes. 5-HT transport by the reconstituted proteoliposomes was saturable, linear with protein (5 to 25 micrograms) and time (15 to 60 s), and optimal with a phospholipid-to-protein ratio of 3:1. There were no significant differences in intravesicular volume, phospholipid-to-protein ratio, and size distribution among the four different groups of proteoliposomes. 5-HT transport was significantly higher and fluorescence anisotropy of DPH was significantly lower in proteoliposomes made from hypoxic phospholipids irrespective of the source of protein. Hypoxia also had a direct effect on the 5-HT transporter since uptake was increased slightly in proteoliposomes from group 3. These results indicate that changes in the plasma membrane phospholipids, and to a much lesser extent changes in the 5-HT transporter, are responsible for increases in the transmembrane transport of 5-HT by hypoxic endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Respir Cell Mol Biol 1992 Jun
PMID:Serotonin transport in reconstituted endothelial cell plasma membrane proteoliposomes: effect of hypoxia. 159 Oct 12

To determine whether a cloned receptor coupled to pertussis toxin (PTx)-sensitive G-proteins can induce cell proliferation and oncogenic transformation, as observed for receptors that elicit PTx-insensitive enhancement of phosphatidyl inositol (PI)-specific phospholipase-C (PLC) activity, nontransformed murine BALB/c-3T3 cells were transfected with the rat serotonin-1A (5-HT1A) receptor. The 5-HT1A receptor is coupled to PTx-sensitive G-proteins to induce a cell-specific activation of PLC. While 1 microM 5-HT induced no change in PI turnover or cytosolic free calcium levels ([Ca2+]i) in receptor-negative nontransfected 3T3 cells, 5-HT induced a 2-fold increase in inositol trisphosphate accumulation and a 2.5-fold increase in [Ca2+]i in the 3T3-ZD8 clone, which expressed 0.6 +/- 0.2 pmol/mg protein of specific 5-HT1A binding sites. The stimulatory actions of 5-HT on PI turnover and [Ca2+]i in 3T3ZD8 cells displayed the pharmacology of the 5-HT1A receptor and were abolished by pretreatment with PTx. Thus, BALB/c-3T3 fibroblast cells express the PLC-linked pathway of the 5-HT1A receptor. Overnight treatment with 5-HT (1 microM) enhanced incorporation of [3H]thymidine into DNA extracted from serum-starved 3T3ZD-8 cells, an action that was also blocked by pretreatment with pertussis toxin. Long term (1-2 weeks) exposure to 5-HT in the medium led to phenotypic transformation of the cells, including the formation of foci with 1 microM 5-HT. These actions of 5-HT were not observed in untransformed 3T3 cells. We conclude that the PTx-sensitive PLC-linked pathway of the 5-HT1A receptor expressed in nontransformed BALB/c-3T3 cells, in concert with other serum-derived factors, predisposes the cells to enhanced proliferation and transformation.
Mol Endocrinol 1992 May
PMID:Conditional transformation mediated via a pertussis toxin-sensitive receptor signalling pathway. 160 83

We have examined the phosphorylation and protein kinase activity of p44 mitogen-activated protein kinase (p44mapk) in growth factor-stimulated hamster fibroblasts using a specific antiserum. The activity of p44mapk was stimulated both by receptor tyrosine kinases and G protein-coupled receptors. Detailed kinetics revealed that alpha-thrombin induces a biphasic activation of p44mapk in CCL39 cells: a rapid phase appearing at 5-10 min was followed by a late and sustained phase still elevated after 4 h. Inactivation of alpha-thrombin with hirudin after 30 sec, which prevented DNA synthesis, did not alter the early p44mapk response but completely abolished the late phase. Pretreatment of the cells with pertussis toxin, which inhibits by more than 95% alpha-thrombin-induced mitogenicity, resulted in the complete loss of late phase activity, while the early peak was partially attenuated. Treatment of CCL39 cells with basic fibroblast growth factor also induced a strong activation of p44mapk. Serotonin, which is not a mitogen by its own, had no effect on late phase p44mapk activity, but synergized with basic fibroblast growth factor to induce late kinase response and DNA synthesis. Both early and late phase activation of p44mapk were accompanied by tyrosine phosphorylation of the enzyme. Together, the results indicate that there is a very close correlation between the ability of a growth factor to induce late and sustained p44mapk activation and its mitogenic potential. Therefore, we propose that sustained p44mapk activation is an obligatory event for growth factor-induced cell cycle progression.
Mol Endocrinol 1992 May
PMID:Biphasic and synergistic activation of p44mapk (ERK1) by growth factors: correlation between late phase activation and mitogenicity. 160 90


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