Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0043167 (pertussis)
 19,595 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The activities of serotonergic antagonists as inverse agonists at the rat 5-hydroxytryptamine (5-HT)2C serotonin receptor were compared with their potencies in promoting receptor "down-regulation," after expression of the recombinant receptor in the baculovirus/Sf9 insect cell system. Baculovirus expression yielded high levels of 5-HT2C receptors (up to 10(6) receptors/cell), which were functionally coupled to polyphosphoinositide turnover in Sf9 cells through a pertussis toxin-insensitive pathway. The expressed receptor exhibited spontaneous activation of inositol phosphate production, which was inhibited in a dose-dependent manner by serotonergic antagonists, consistent with inverse agonist activity. The potencies of antagonists as inverse agonists correlated with their respective binding affinities determined in competition binding studies with membrane preparations. The maximal inhibition of spontaneous activity ranged from 32% inhibition for mianserin to no effect for spiroxatrine, indicating that antagonists differ in their intrinsic inverse efficacies. Antagonist treatment of intact Sf9 cells or membranes containing the 5-HT2C receptor, followed by washout of residual drug, resulted in a decrease (up to 90%) in the number of binding sites for [3H]mesulergine and [3H]5-HT, with no change in the affinity for [3H]mesulergine. The decrease in binding was irreversible, was not due to the presence of residual antagonist, and was not observed after treatment with agonists. This effect of antagonists in membranes was dose dependent, but the rank order of potency was clearly different from that for inverse agonist activity, indicating that the two effects reflect distinct actions of antagonists at the 5-HT2C receptor. The relative abilities of antagonists to produce loss of binding showed a good correlation with their reported abilities to down-regulate 5-HT2 receptors in vivo after chronic treatment, suggesting that these actions reflect the same underlying process.
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PMID:Serotonergic antagonists differentially inhibit spontaneous activity and decrease ligand binding capacity of the rat 5-hydroxytryptamine type 2C receptor in Sf9 cells. 762 69

The serotonin 5-HT2C receptor (formerly designated the 5-HT1C receptor) of the choroid plexus triggers phosphoinositide turnover. In the present study, we demonstrate that receptor activation also triggers the formation of cyclic GMP (cGMP). Application of 1 microM 5-HT to porcine choroid plexus tissue slices resulted in stimulation of cGMP formation to a maximum of five-fold basal level, with an EC50 of 11 nM. This response was not inhibited by muscarinic or beta-adrenergic receptor antagonists. Serotonin receptor antagonists inhibited cGMP formation with apparent Ki values of 1.3 (mianserin), 200 (ketanserin), and 5,500 (spiperone) nM, respectively. Neither serotonin-stimulated cGMP formation nor PI turnover was inhibited by pertussis toxin pretreatment. Preliminary biochemical studies suggested that serotonin-stimulated cGMP formation was calcium, phospholipase A2, and lipoxygenase dependent, as incubation in low calcium buffers or inclusion of the phospholipase A2 or lipoxygenase inhibitors p-bromophenacylbromide or BW 755c resulted in significant reduction of cGMP formation. The present results suggest that in addition to triggering phosphoinositide turnover, choroid plexus serotonin 5-HT2C receptors trigger cGMP formation in a calcium-sensitive manner.
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PMID:Serotonin 5-HT2C receptor stimulates cyclic GMP formation in choroid plexus. 779 14

Serotonin2A (5-HT2A) and 5-HT2C receptors share numerous pharmacological properties. Two compounds thought to discriminate between these two receptor subtypes are m-chlorophenypiperazine (mCPP) and m-trifluoromethylphenylpiperazine (TFMPP). These two drugs have been classified as antagonists at 5-HT2A receptors but as agonists at 5-HT2C receptors on the basis of phosphoinositide hydrolysis studies in cerebral cortex and choroid plexus, respectively. To determine more fully the properties of mCPP and TFMPP at 5-HT2A receptors, NIH 3T3 fibroblasts transfected with the 5-HT2A receptor complementary DNA (GF6 cells) were used as a model system of receptor function. These cells express approximately 15-fold higher 5-HT2A receptor density than is found in cerebral cortex. In GF6 cells, mCPP and TFMPP dose-dependently stimulated phosphoinositide hydrolysis with maximal effects less than that of 5-HT. This agonist activity was blocked by 5-HT2A receptor antagonists but not by prior treatment with pertussis toxin. Partial inactivation of 5-HT2A receptors with phenoxybenzamine decreased the maximal effects of mCPP and TFMPP but did not eliminate agonist activity. Thus mCPP and TFMPP are partial agonists at 5-HT2A receptors in GF6 cells, and these agonist properties are retained even under conditions where receptor density is comparable to that of cerebral cortex. Although it has not yet been demonstrated that mCPP and TFMPP are agonists at central 5-HT2A receptors, this possibility should be considered when evaluating in vivo effects of these drugs.
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PMID:m-chlorophenylpiperazine and m-trifluoromethylphenylpiperazine are partial agonists at cloned 5-HT2A receptors expressed in fibroblasts. 796 73

Previous studies have shown that agonist activation of the 5-hydroxytryptamineC (5-HT2C) receptor expressed in NIH-3T3 fibroblasts results in development of a transformed phenotype. In light of recent evidence from our laboratory demonstrating constitutive 5-HT2C receptor activity, we examined the contribution of this agonist-independent activity to basal cell division. 5-HT2C receptor ligands modulated [3H]thymidine incorporation, DNA amounts, and cell number in serum-starved NIH-3T3 fibroblasts transfected with 5-HT2C receptor cDNA. Three classes of 5-HT2C receptor ligands were distinguished in transfected, but not nontransfected, fibroblasts. Basal [3H]thymidine incorporation was increased by agonists and decreased by inverse agonists, whereas neutral antagonists had little or no effect alone. Neutral antagonists did, however, block the effects of both agonists and inverse agonists. The rank order of potencies of inverse agonists to decrease basal [3H]thymidine incorporation was consistent with their rank order to decrease basal 5-HT2C receptor-mediated phosphoinositide hydrolysis. However, two antagonists previously classified as inverse agonists based on their ability to eliminate basal phosphoinositide hydrolysis did not elicit comparable reductions in basal [3H]thymidine incorporation. For example, mesulergine had no effect on basal cell division, even though it eliminates the phosphoinositide hydrolysis response. Pertussis toxin, which inactivates G proteins in the Gi and Go families, had no effect on basal [3H]thymidine incorporation or basal phosphoinositide hydrolysis but partially inhibited these responses when elicited by an agonist. Thus, agonist occupation of the 5-HT2C receptor apparently activates different or additional G proteins compared with constitutive 5-HT2C receptor activation. In conclusion, our findings suggest that constitutively active 5-HT2C receptors stimulate cell division in transfected fibroblasts in the absence of an agonist. In addition, the 5HT2C receptor may use multiple signaling pathways to mediate its effects.
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PMID:Differences in agonist-independent and -dependent 5-hydroxytryptamine2C receptor-mediated cell division. 864 87

1. Whole-cell Ca2+ currents (ICa) from cultured rat melanotrophs were identified by their sensitivity to Ca2+ channel blockers, and their modulation by serotonin (5-HT) was studied. All cells displayed high voltage-activated (HVA; > -30 mV) Ca2+ currents. A low voltage-activated (LVA; > -60 mV) Ca2+ current was detected in 92% of the cells. 2. The whole-cell ICa was insensitive to omega-conotoxin GVIA (0.5-1 microM) indicating the absence of N-type Ca2+ channels. 3. At a holding potential (Vh) of -70 mV, the L-type channel blocker nifedipine reduced ICa in a dose-dependent manner with a half-maximal effective concentration (IC50) of 28 nM. The L-type current represented 39% of the total ICa. 4. omega-Agatoxin IVA (omega-Aga IVA) produced a biphasic dose-dependent inhibition of ICa, with IC50 values of 0.4 and 91 nM, indicating the presence of P-type and Q-type Ca2+ channels, which accounted respectively for 16 and 45% of the total ICa. The P-type current was also blocked by synthetic funnel-web spider toxin (sFTX 3.3; 1-10 microM) and was present only in a subpopulation (60-70%) of cells. 5. All cells possessed a Ca2+ current which was resistant to nifedipine (10 microM) and omega-Aga IVA (50 nM). This current was not affected by Ni2+ (40 microM) but was abolished by a low concentration of Cd2+ (10 microM) and by omega-conotoxin MVIIC (1 microM) indicating that it was a Q-type Ca2+ current. 6. 5-HT (10 microM) inhibited the whole-cell ICa in 70% of the cells tested (n = 120) by activating 5-HT1A and 5-HT2C receptors. 5-HT produced either a kinetic slowing of the activation phase (37% of the cells) or a scaling down (14% of the cells) of ICa. In the majority of cells (49%) both types of inhibition were found to coexist. 7. The effects of 5-HT were voltage dependent, rendered irreversible when GTP-gamma-S (30 microM) was present in the pipette solution and abolished by pretreatment of the cells with pertussis toxin (PTX; 150 ng ml-1, 18 h). 8. Low concentrations of omega-Aga IVA (20 nM), which blocked mainly P-type channels, did not reduce the effect of 5-HT on ICa. The scaling down effect of 5-HT on ICa was eliminated in the presence of nifedipine (10 microM) and the kinetic slowing effect of 5-HT persisted after blockade of L- and P-type channels but was abolished by omega-conotoxin MVIIC (1 microM). 9. We conclude that rat melanotrophs possess functional L-, P- and Q-type Ca2+ channels and that 5-HT inhibits selectively L-type and Q-type Ca2+ currents with different modalities. These effects are voltage dependent and mediated by a PTX-sensitive G-protein.
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PMID:Selective inhibition of high voltage-activated L-type and Q-type Ca2+ currents by serotonin in rat melanotrophs. 868 60

We studied the endogenous expression of the serotonin-2A (5-hydroxytryptamine2A, 5-HT2A) 5-HT2C, and a splice-variant of the 5-HT2C receptor in murine Balb/c-3T3 fibroblast cells that is revealed when these cells are maintained in medium containing 5-HT-free serum. RNA editing of the 5-HT2C receptor was exclusively at a single brain-specific site. Addition of 5-HT (EC50 = 23 +/- 2.9 nM) induced an immediate release of calcium from an ionomycin-sensitive intracellular store by coupling to a pertussis toxin-insensitive pathway. The 5-HT-induced calcium mobilization displayed a 5-HT-2-like pharmacology, and ligand binding analyses indicated the presence of specific binding sites (27.5 +/- 2 fmol/mg protein) with a 5-HT2A-like pharmacology. Although the 5-HT2A receptor site was predominant, the smaller component of 5-HT2C receptors alone was sufficient to mediate a maximal calcium response. The 5-HT-induced increase in [Ca2+]i was reversibly inhibited by >75% following a 12-hr pretreatment (T1/2 = 2 hr) with 5-HT (EC50 = 400 nM). Extended treatment (24-96 hr) with 5-HT induced a complete functional desensitization that was associated with a partial (60%) reduction in 5-HT2 receptor number, implicating both receptor down-regulation and post-receptor mechanisms in 5-HT-induced desensitization. Long-term (hours to days) treatment with 5-HT did not modulate DNA synthesis, cell proliferation, or transformation in Balb/c-3T3 cells. These results demonstrate that Balb/c-3T3 cells express endogenous 5-HT2 receptors that are desensitized by the 5-HT present in normal serum, illustrating the importance of growth conditions in the identification of receptor responsiveness. The lack of proliferative response to 5-HT in Balb/c-3T3 suggests a putative role of desensitization as a "safety valve" to prevent abnormal cell growth during sustained 5-HT2 receptor activation.
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PMID:Endogenous serotonin-2A and -2C receptors in Balb/c-3T3 cells revealed in serotonin-free medium: desensitization and down-regulation by serotonin. 982 34