Localizing Drug and Neurotransmitter Receptors in Vivo with Tritium-Labeled Tracers
William C. Eckelman, Lelio G. Colombetti in Receptor-Binding Radiotracers, 2019
A binding site may be identified and considered a receptor for a drug or neurotransmitter or hormone only after a careful comparison of the properties of the binding site with the properties expected of the related receptor.1 Thus, the binding site should be present in relatively limited numbers and in relevant tissues. It is expected that the binding ligands will have a relatively high affinity for the receptor, and that the binding kinetics should reflect the rates of production and loss of biological effects of the drugs or hormones. A very useful criterion is that of pharmacological specificity; drugs and neurohormones that vary in their potency in the production of biological responses should vary in their potency at the binding site in the same rank order. An exact matching of binding properties with expected receptor properties argues strongly for a receptor identification for the binding site. In in vitro studies, the final proof or acceptance of receptor identification usually requires purification of the binding site and the further demonstration that adding the purified binding site, perhaps with other molecular components to model membrane systems, results in the establishment of a receptor response that is indistinguishable from that observed in intact tissues. In in vitro studies, yet other experiments are commonly performed in the attempt to identify receptors. These include temperature inactivation, effects of ions, subcellular distributions studies, and metabolism studies.
Selective estrogen receptor modulators as a new postmenopausal prevention- maintenance therapy
Barry G. Wren in Progress in the Management of the Menopause, 2020
At the subcellular level it is now known that there is target site localization of different receptor molecules. The conventional estrogen receptors have been recognized for 30 years but a novel estrogen receptor (ER)4322has just been described (Figure 3). Alternatively, inhibitory or stimulatory factors could be located in different tissues that ultimately control whether a ligand receptor complex will be an inhibitory or stimulatory signal. These associated proteins are a topic of intense investigation23. Finally the genes in a target tissue may be activated or blocked specifically because a receptor ligand complex binds differentially to sites in a targeted promoter region. A raloxifene response element has been described in the promoter region of the transforming growth factor (TGF)-13 gene that might be responsible for differential bone stimulation24 (Figure 4). With all these possibilities, the actions of a targeted agent could be the result of one of several or all mechanisms.
Growth Factor Receptors
Enrique Pimentel in Handbook of Growth Factors, 2017
After formation of the ligand-receptor complex, the receptor undergoes a specific conformational change, which in some manner induces the generation of intracellular transducing signals that lead to a cellular response. For transmembrane receptors such as those of growth factors, the postreceptor signal transduction mechanisms may include the activation of GTP-binding proteins (G proteins), the regulation of plasma membrane ion channels, and the phosphorylation of proteins on tyrosine and/or serine/threonine residues.11,12 The actions caused by growth factors, hormones, regulatory peptides, and other ligands in their target cells may result, on the one hand, from a given receptor acting selectively on unique substrates in a single cell type and, on the other hand, from the same receptor acting on different substrates in different types of cells.13 In any case, the genetic program expressed by a particular cell is of crucial importance for the specificity of the physiologic response.
The enigmatic nature of the triggering receptor expressed in myeloid cells -1 (TLT- 1)
Published in Platelets, 2021
Siobhan Branfield, A. Valance Washington
Key to understanding the function of any receptor is the identification of its ligand. In our early studies we proposed fibrinogen as a ligand of TLT-1 and suggested that during platelet aggregation, TLT-1 cross-links extracellular fibrinogen, stabilizing higher-order platelet aggregates [18]. In this study, lysates generated from purified human platelets were applied to AminoLink columns preloaded with either sTLT-1 or sTREM-1. This approach revealed specific binding of 3 proteins with molecular masses between 50 and 80 kDa on a Coomassie stained gel. Mass spectroscopy identified these proteins as the α, β, and γ chains of fibrinogen. To confirm these findings, fibrinogen was also eluted from His-tagged TLT-1 but not TREM-1 bound to nickel columns and resolved by PAGE in either native or reduced conditions. Consistent with disulfide-linked multimers of fibrinogen, TLT-1 column specifically bound a high molecular weight complex that when reduced resolved into the same 3 bands detected with AminoLink columns. Immunoblotting with anti-fibrinogen confirmed the identity of these TLT-1–interacting proteins as fibrinogen. This was further supported by ELISA, confirming fibrinogen as a TLT-1 ligand. While the identification of fibrinogen as a ligand was expected to bring answers, it only generated larger questions.
Possible effects of different doses of 2.1 GHz electromagnetic radiation on learning, and hippocampal levels of cholinergic biomarkers in Wistar rats
Published in Electromagnetic Biology and Medicine, 2021
Çiğdem Gökçek-Saraç, Güven Akçay, Serdar Karakurt, Kayhan Ateş, Şükrü Özen, Narin Derin
Cholinergic neurons by having an intense projection of fibers through the hippocampus (Prado et al. 2017; Wevers 2011) are involved in many cognitive functions such as learning, memory, arousal, movement, sleep, attention (Rima et al. 2020), and that the loss of central cholinergic neurons is observed in some of the neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases (Parhizkar et al. 2017; Rima et al. 2020). Acetylcholine, the primary neurotransmitter of the cholinergic system, is synthesized by choline acetyltransferase (ChAT) by the choline and acetyl-CoA (Deiana et al. 2011; Oda 1999). In the synaptic terminals, acetylcholine that is stored in the synaptic vesicles by vesicular acetylcholine transporters (VAChT), is released into the synaptic cleft as a result of an action potential and it binds either to post-synaptic receptors on cell or pre-synaptic receptors on the neurons that it is released (Ferreira-Vieira et al. 2016). Upon binding to its receptor, a biological response is generated. Acetylcholinesterase (AChE) that is located at the postsynaptic membrane of the synapse catalyses the conversion of acetylcholine molecule and water into acetic acid and choline (Oda 1999). Products of this reaction can be returned to the presynaptic terminal via the re-uptake process (Oda 1999).
Pharmacological modulation of P2X4 in inflammatory bowel diseases: the way towards novel therapeutics?
Published in Journal of Drug Targeting, 2023
Vanessa D’Antongiovanni, Carolina Pellegrini, Matteo Fornai, Zoltan H. Nemeth, György Haskó, Luca Antonioli
P2X4R is distributed throughout the body; indeed, it is widely expressed in central and peripheral neurons, microglia, immune cells, endothelial cells and even in glandular tissues [8]. At the cellular level, this receptor is located not only on the plasma membrane, but also in intracellular compartments, such as lysosomes, vesicles, vacuoles, and lamellar bodies [8]. Due to the wide body distribution, P2X4R plays a pivotal role in regulating several physiological functions, such as synaptic transmission, muscle contraction, exocrine secretion, platelet aggregation and macrophage activation, as well as in the development of inflammatory diseases, including post-ischaemic inflammation, rheumatoid arthritis, asthma, neurodegenerative and cardiovascular diseases as well as IBDs [8,12–14]. Indeed, in response to injury or noxious stimuli, a large amount of ATP is released in the extracellular space triggering P2X4-mediated pro-inflammatory cascade (Figure 1). The activation of P2X4R in immune cells promotes intracellular pro-inflammatory signalling pathways, such as AKT (protein-chinasi B), JNK (c-Jun N-terminal kinases), MAPK (mitogen-activated protein kinase), NLRP3 (nucleotide-binding oligomerisation domain leucine rich repeat and pyrin domain containing protein 3) and PKA/PKC (cAMP-dependent protein kinase A/protein kinase C) signalling (Figure 1) [15–17]. In addition, activated P2X4R regulates calcium signalling propagation and induces the releases of damaging factors, such as TNF, ROS (reactive oxygen species) and IL-1β, with consequent onset/maintenance of immune-inflammatory responses (Figure 1) [15–17].
Related Knowledge Centers
- Biochemistry
- Electrophysiology
- Gabaa Receptor
- Ligand
- Protein
- Signal Transduction
- Neurotransmitter
- Pharmacology
- Signs & Symptoms
- Γ-Aminobutyric Acid