Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01189 (beta-endorphin)
 21,003 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In C6 glial cells stably expressing rat mu-opioid receptor, opioid agonist activation is negatively coupled to adenylyl cyclase through pertussis toxin-sensitive G proteins. In membranes, [D-Ala2, N-MePhe4,Gly-ol5]enkephalin (DAMGO) increases guanosine-5'-O-(3-[35S]thio)triphosphate (GTP[gamma-35S]) binding by 367% with an EC50 value of 28 nM. Prolonged exposure to agonists induced desensitization of the receptor as estimated by a reduction in the maximal stimulation of GTP[gamma-35S] binding by DAMGO and rightward shifts in the dose-response curves. In cells treated with 10 microM concentrations of etorphine, DAMGO, beta-endorphin, morphine, and butorphanol, DAMGO-stimulated GTP[gamma-35S] binding was 58%, 149%, 205%, 286%, and 325%, respectively. Guanine nucleotide regulation of agonist binding was correspondingly lower in membranes from tolerant cells. Furthermore, chronic opioid treatment increased forskolin-stimulated adenylyl cyclase activity, and potency of DAMGO to inhibit cAMP accumulation was lower in morphine- and DAMGO-tolerant cells (EC50 = 55 and 170 nM versus 18 nM for control). Chronic treatment with agonists reduced [3H]DAMGO binding in membranes with the rank order of etorphine > DAMGO = beta-endorphin > morphine > butorphanol, and the affinity of DAMGO in alkaloid- but not peptide-treated membranes was significantly lower in comparison with control. Pertussis toxin treatment of the cells before agonist treatment did not prevent the down-regulation by full agonists; DAMGO and etorphine exhibited approximately 80% internalization, whereas the ability of partial agonists was greatly impaired. In addition to establishing this cell line as a good model for further studies on the mechanisms of opioid tolerance, these results indicate important differences in the inactivation pathways of receptor triggered by full and partial agonists.
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PMID:Down-regulation of mu-opioid receptor by full but not partial agonists is independent of G protein coupling. 935 81

The interaction between corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) is important in the regulation of adrenocorticotropin (ACTH) release from the anterior pituitary (AP). CRF exerts its effect on the AP by activating the adenylate cyclase (AC) complex whereas AVP increases the turnover of phosphatidylinositol. In the rat and in man, CRF is the most potent ACTH secretagogue whereas AVP alone is only a weak agonist. Since recent studies in the sheep indicate a reversal of this order of potency, these studies were undertaken to test the hypothesis that a functional alteration of the AC in the ovine corticotrope might limit the ability of CRF to release ACTH from these cells. When rat AP cells were incubated with CRF, a dose-dependent increase in AC activity was observed. This effect was potentiated either by AVP or PMA, although neither agent alone altered AC activity. In contrast, CRF alone, or in combination with AVP or PMA, did not increase AC activity in ovine AP cells. Both cholera toxin (CT) and pertussis toxin (PT) caused a dose-dependent release of ACTH from rat and ovine AP cells, but the amount of ACTH released from the ovine AP cells by both agents was relatively reduced. In the ovine cells, however, AVP acted synergistically with CT or PT to markedly increase the release of ACTH to levels which approached those obtained when the rat AP cells were exposed to CT or PT alone. Forskolin increased AC activity in AP cells of both species, but to a much lower extent in ovine cells than in the rat cells. However, when the ovine cells were exposed to AVP, the AC response to forskolin became similar to the response observed in the rat cells when incubated with forskolin alone. Forskolin also released significantly less ACTH from the ovine AP cells, but AVP also acted synergistically with forskolin to greatly enhance the amount of ACTH released from these cells. Finally, 8-bromo-cyclic AMP produced a similar release of ACTH from both ovine and rat AP cells. We conclude that: (1) the decreased ability of CRF to increase ACTH release from the ovine AP reflects a net decrease in AC activity and cannot be ascribed to an ovine corticotropic resistance to cAMP; (2) the decreased activity of the ovine corticotropic AC complex may in turn reflect functional alterations at the level of both the G proteins and the catalytic subunit; (3) since AVP causes protein kinase C substrate phosphorylation in the ovine AP, AVP may increase AC activity in this tissue by phosphorylating the G proteins and/or the catalytic subunit.
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PMID:A comparative study of the role of adenylate cyclase in the release of adrenocorticotropin from the ovine and rat anterior pituitary. 939 50

1. The actions of the neuropeptide nociceptin on the calcium channel currents (IBa) of acutely dissociated rat periaqueductal grey (PAG) neurons were examined using whole-cell patch clamp techniques. These effects were compared with those of opioid receptor agonists and the GABAB receptor agonist baclofen. 2. Neurons from young adult rats (23 to 56 days old) expressed predominantly omega-conotoxin GVIA (N-type)- and omega-agatoxin IVA (P/Q-type)-sensitive IBa, together with smaller amounts of nimodipine-sensitive current and current resistant to all three blockers. There was proportionately more N-type IBa in neurons from female rats and proportionately more resistant current in neurons from male rats. 3. Nociceptin (EC50, 5 nM) and baclofen (EC50, 0.8 microM) inhibited IBa in all PAG neurons, while the opioid agonist methionine enkephalin (met-enkephalin; 300 nM-10 microM) inhibited IBa in 40 % of neurons. The effects of met-enkephalin were reversed by the mu-opioid antagonist CTAP, and mimicked by the mu-opioid agonist DAMGO (300 nM-3 microM). The delta-opioid agonists DPDPE and deltorphin II, and the kappa-opioid agonist U69593, did not affect IBa in any neuron. The actions of nociceptin were not mimicked or blocked by the opioid antagonist naloxone or the nociceptin analogue [desPhe1]-nociceptin. 4. The effects of nociceptin and baclofen on IBa were blocked by pretreatment of the neurons with pertussis toxin (500 ng ml-1, 8 h). 5. Nociceptin predominantly inhibited the N-type (EC50, 2 nM; maximum inhibition, 50 %) and P/Q-type (EC50, 7 nM; maximum inhibition, 33 %) IBa while having little effect on the L-type and R-type IBa. 6. These results are consistent with the previously described actions of nociceptin, baclofen and micro-opioids in PAG slices, whereby they couple to increases in an inwardly rectifying K+ conductance. These agonists thus have the potential to modulate the function of PAG neurons via a number of different cellular effectors.
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PMID:Modulation of Ca2+ channel currents of acutely dissociated rat periaqueductal grey neurons. 954 80

An intact chemotactic response is vital for leukocyte trafficking and host defense. Opiates are known to exert a number of immunomodulating effects in vitro and in vivo, and we sought to determine whether they were capable of inhibiting chemokine-induced directional migration of human leukocytes, and if so, to ascertain the mechanism involved. The endogenous opioid met-enkephalin induced monocyte chemotaxis in a pertussis toxin-sensitive manner. Met-enkephalin, as well as morphine, inhibited IL-8-induced chemotaxis of human neutrophils and macrophage inflammatory protein (MIP)-1alpha, regulated upon activation, normal T expressed and secreted (RANTES), and monocyte chemoattractant protein 1, but not MIP-1beta-induced chemotaxis of human monocytes. This inhibition of chemotaxis was mediated by delta and micro but not kappa G protein-coupled opiate receptors. Calcium flux induced by chemokines was unaffected by met-enkephalin pretreatment. Unlike other opiate-induced changes in leukocyte function, the inhibition of chemotaxis was not mediated by nitric oxide. Opiates induced phosphorylation of the chemokine receptors CXCR1 and CXCR2, but neither induced internalization of chemokine receptors nor perturbed chemokine binding. Thus, inhibition of chemokine-induced chemotaxis by opiates is due to heterologous desensitization through phosphorylation of chemokine receptors. This may contribute to the defects in host defense seen with opiate abuse and has important implications for immunomodulation induced by several endogenous neuropeptides which act through G protein-coupled receptors.
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PMID:Opiates transdeactivate chemokine receptors: delta and mu opiate receptor-mediated heterologous desensitization. 967 44

In membranes of the rat frontal cortex, acetylcholine (ACh) and other cholinergic agonists were found to potentiate the stimulation of adenylyl cyclase activity elicited by corticotropin-releasing hormone (CRH). Oxotremorine-M, carbachol and methacholine were as effective as ACh, whereas oxotremorine and arecoline were much less effective. The facilitating effect of Ach was potently blocked by the M1 antagonists R-trihexyphenidyl, telenzepine and pirenzepine and by the M3 antagonists hexahydro-sila-difenidol and p-fluorohexahydro-sila-difenidol, whereas the M2 and M4 antagonists himbacine, methoctramine, AF-DX 116 and AQ-RA 741 were less potent. The mamba venom toxin MT-1, which binds with high affinity to M1 receptors, was also a potent blocker. The pharmacological profile of the muscarinic potentiation of CRH receptor activity was markedly different from that displayed by the muscarinic inhibition of forskolin-stimulated adenylyl cyclase, which could be detected in the same membrane preparations. Moreover, the intracerebral injection of pertussis toxin impaired the muscarinic inhibition of cyclic AMP formation and reduced the Ach stimulation of [35S]GTPgammaS binding to membrane G proteins but failed to affect the facilitating effect on CRH receptor activity. The latter response was also insensitive to the phospholipase C inhibitor U-73122, the protein kinase inhibitor staurosporine and to the inhibitors of arachidonic acid metabolism indomethacin and nordihydroguaiaretic acid. These data demonstrate that in the rat frontal cortex, muscarinic receptors of the M1 subtype potentiate CRH transmission by interacting with pertussis toxin-insensitive G proteins.
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PMID:Identification and characterization of muscarinic receptors potentiating the stimulation of adenylyl cyclase activity by corticotropin-releasing hormone in membranes of rat frontal cortex. 969 30

Our laboratory demonstrated that adenosine inhibits the activation of adenylyl cyclase and the secretion of the alpha-melanocyte-stimulating hormone (alpha-MSH) from the intermediate lobe of the frog pituitary. This paper showed the bioelectric effects induced by adenosine, the ionic conductances modulated by adenosine, and the possible involvement of intracellular messengers, indicated the mechanism by which adenosine controls the secretion of alpha-MSH. The results show that adenosine acting on A1 adenosine receptor subtype reduced the Ca2+ influx necessary for the secretion, through 4 distinct mechanisms: 1) a hyperpolarization resulting from the activation of a voltage-insensitive K+ conductance, 2) a reduction of the duration of spontaneous action potentials due to an increase of the outward delayed rectifyer K+ current (lk), 3) a diminution of the cellular excitability by an activation of the transient outward K+ current (lA), and 4) an inhibition of the L- and N-type Ca2+ currents, with a predominant action on the N-type component. Cell dialysis with GTP gamma S rendered irreversible the effects of adenosine on the K+ conductances and Ca2+ channels, whereas PTX pretreatment totally abolished the response to adenosine, suggesting all bioelectric effects of adenosine were mediated by pertussis toxin-sensitive G proteins. Whether the implicated G proteins regulate the K+ and Ca2+ channels by tight-coupling or via a second-messenger system remains to be solved. With our results, the involvement of adenylyl cyclase can be excluded because addition of cAMP and IBMX, an inhibitor of phosphodiesterases, in the intracellular solution, or application of dibutyryl cAMP in the extracellular solution did not modify the adenosine-induced responses.
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PMID:Patch clamp study on mechanism of adenosine-induced inhibitory effects in frog pituitary melanotrophs. 986 55

Under control incubation conditions, gonadotropin-releasing hormone (GnRH) binds only a fraction of its receptors in rat-cultivated pituitary cells. Unmasking of the remaining receptors, which have been termed 'cryptic', requires drug- or peptide-induced protein kinase activation. Spontaneous masking however is not observed on pituitary cells sampled from castrated male rats, suggesting the presence of an intrinsic unmasking factor. Many endogenous factors could theoretically account for the effect. Here we attempted to identify the factor involved by taking advantage of their differential dependency upon second messengers and transduction cascades. Spontaneous unmasking of GnRH binding was found reversed by pertussis toxin (PTX), an inhibitor of alphai and alphao subunits of heterotrimeric G proteins, and by U73122, a phospholipase C (PLC) inhibitor. In contrast, desensitization of protein kinase C (PKC) or inhibition of tyrosine kinase by herbimycin were ineffective. Among endogenous pituitary factors able to unmask GnRH receptors in pituitary cells from normal male rats, as EGF, NPY or opiate peptides, only the latter were found to correspond to this transduction profile. In an attempt to characterize the pharmacology of opiate effects, naloxone (10 microM), a poorly selective opiate antagonist, restored masking of GnRH binding in cells from castrates. Only the delta antagonist naltrindole (1 microM) was able to mimick the action of naloxone. Conversely, when tested on cells from intact animals, morphine (10 microM), as well as dslet (1 microM) and met-ENK (10 nM), preferential delta agonists, but not dago and beta-endorphin or U50488 H and dynorphin, respectively micro and kappa agonists, were able to suppress masking. Among opioid peptides endogenous to the pituitary, only met-ENK was able to unmask cryptic receptors, an effect antagonized by naltrindole. We conclude that an opiate delta receptor subtype is endogenously activated in the pituitary of castrated male rats to prevent masking of GnRH binding.
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PMID:Delta opiate receptors account for the castration-induced unmasking of gonadotropin-releasing hormone binding sites in the rat pituitary. 987 2

In the present study, we examined the ability of several putative neurotransmitters and neuromodulators to modulate voltage-dependent Ca2+ channel currents in adult rat intracardiac neurons. Of 17 compounds tested, acetylcholine (Ach), neuropeptide Y (NPY), norepinephrine (NE), and met-enkephalin (met-Enk) were effective modulators of the Ca2+ currents. The neurotransmitter-induced current inhibition was associated with slow activation kinetics and relief by a strong depolarizing prepulse. Overnight pretreatment of neurons with pertussis toxin (PTX, 500 ng/ml) significantly attenuated the neurotransmitter-induced current inhibition. Heterologous expression of transducin, a known chelator of G-protein betagamma subunits, almost completely abolished the neurotransmitter-induced current inhibition. Taken together, our data suggest that four different neurotransmitters inhibit the Ca2+ channel currents in adult rat intracardiac neurons via a pathway that is voltage-dependent, membrane-delimited, and utilizes betagamma subunits released from PTX-sensitive G-proteins. The Ca2+ channel inhibition by non-cholinergic neurotransmitters may play important roles in regulation of neuronal excitability and Ach release at synapses in intracardiac ganglia, thereby contributing to cholinergic control of cardiac functions.
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PMID:Activation of various G-protein coupled receptors modulates Ca2+ channel currents via PTX-sensitive and voltage-dependent pathways in rat intracardiac neurons. 1032 8

In mice whose Gi/o-protein function had been impaired by antisense 'knock-down' or pertussis toxin treatment, i.c.v. injection of myr+-Gi/o alpha subunits restored the effectiveness of beta-endorphin, morphine, DPDPE, clonidine and neurotensin to produce antinociception. Myr+-G alpha subunits of the class of G-proteins actually impaired were more effective than unlike but related myr+-G alpha subunits. Selectivity was noted in that only exogenous myr+-G alpha subunits affected (enhanced) the activity of agonists in G alpha-deficient signalling systems. This treatment had little effect on agonist potency when the impairment resided at the receptor level. The potential of the opioids, clonidine and R-PIA to increase G alpha-related in vitro hydrolysis of GTP was also re-established after injecting myr+-Gi2 alpha subunits into Gi2-knocked-down mice. Myr+-Gi2 alpha subunits pre-incubated with GTPgammaS or GDPbetaS before i.c.v. injection did not improve the activity of agonists in vivo (antinociception) or in vitro (regulation of low Km GTPase). After impairing the function of PKCbeta1 by antisense treatment or with the inhibitor H7, the effect of myr+-G alpha subunits on agonist potency was prevented. Electron microscope analysis showed the entry of gold-conjugated myr+-G alpha subunits into neural cells. These particles were found in the cytoplasm, associated with the plasma membranes of different neuronal processes and also in synaptic junctions. In cultured neurons and astrocytes myr+-Gi2 alpha-associated fluorescence was internalised in a dose-dependent manner and distributed in the plasma membrane and cytosol, as well as in nuclei of dividing astrocytes. Thus, G alpha subunits in CSF enter into neurons and functionally couple to the receptor-triggered signalling cascade. As G-proteins have been implicated in the pathophysiology of several neural disorders, this finding may be valuable in the therapy of such dysfunctions.
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PMID:Myr+-Gi2 alpha and Go alpha subunits restore the efficacy of opioids, clonidine and neurotensin giving rise to antinociception in G-protein knock-down mice. 1060 81

The primary structure of frog neurotensin (fNT) has recently been determined and it has been shown that fNT is a potent stimulator of alpha-MSH secretion by frog pituitary melanotropes. In the present study, we have investigated the effects of fNT on the electrical activity of cultured frog melanotropes by using the patch-clamp technique and we have determined the pharmacological profile of the receptors mediating the effect of fNT. In the cell-attached configuration, fNT (10(-7) M) provoked an increase in the action current discharge followed by an arrest of spike firing. In the gramicidin-perforated patch configuration, fNT (10(-7) M) induced a depolarization accompanied by an increase in action potential frequency and a decrease in membrane resistance. Administration of graded concentrations (10(-10) to 10(-6) M) of fNT or the C-terminal hexapeptide NT(8-13) caused a dose-dependent increase in the frequency of action potentials with EC(50) of 2 x 10(-8) and 5 x 10(-9) M, respectively. The stimulatory effect of fNT was mimicked by various pseudopeptide analogs, with the following order of potency: Boc-[Trp(11)]NT(8-13) > Boc-[D-Trp(11)]NT(8-13) > Boc-[Lys(8,9), Nal(11)]NT(8-13) > Boc-[Psi11,12]NT(8-13). In contrast, the cyclic pseudopeptide analogs of NT(8-13), Lys-Lys-Pro-D-Trp-Ile-Leu and Lys-Lys-Pro-D-Trp-Glu-Leu-OH, did not affect the electrical activity. The NTS1 receptor antagonist and nts2 receptor agonist SR 48692 (10(-5) M) stimulated the spike discharge but did not block the response to fNT. In contrast, SR 142948A (10(-5) M), another NTS1 receptor antagonist and nts2 receptor agonist, inhibited the excitatory effect of fNT. The specific nts2 receptor ligand levocabastine (10(-6) M) had no effect on the basal electrical activity and the response of melanotropes to fNT. In cells which were dialyzed with guanosine-5'-O-(3-thiotriphosphate) (10(-4) M), fNT caused an irreversible stimulation of the action potential discharge. Conversely, dialysis of melanotropes with guanosine-5'-O-(2-thiodiphosphate) (10(-4) M) completely blocked the effect of fNT. Pretreatment of cells with cholera toxin (1 microg/ml) or pertussis toxin (0.2 microg/ml) did not affect the electrical response to fNT. Intracellular application of the G(o/i/s) protein antagonist GPAnt-1 (3 x 10(-5) M) had no effect on the fNT-evoked stimulation. In contrast, dialysis of melanotropes with the G(q/11) protein antagonist GPAnt-2A (3 x 10(-5) M) abrogated the response to fNT. The present data demonstrate that fNT is a potent stimulator of the electrical activity of frog pituitary melanotropes. These results also reveal that the electrophysiological response evoked by fNT can be accounted for by activation of a G(q/11)-protein-coupled receptor subtype whose pharmacological profile shares similarities with those of mammalian NTS1 and nts2 receptors.
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PMID:Neurotensin modulates the electrical activity of frog pituitary melanotropes via activation of a G-protein-coupled receptor pharmacologically related to both the NTS1 and nts2 receptors of mammals. 1114 21


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