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Human endocannabinoid signaling is primarily mediated by the cannabinoid receptors, CB1 and CB2, which are G protein-coupled receptors (GPCRs). These receptors have been linked to a variety of physiological processes and are being pursued as prospective drug targets due to their potential in treating pain and inflammation. However, because of their homology and shared signaling mechanisms, investigating the individual physiological roles of these receptors and designing subtype-selective ligands has been challenging. Using active-state CB1 and CB2 structures as guides, homologous residues within the orthosteric pocket of each receptor were mutated to alanine to test whether they equally impair CB1 and CB2 activity in response to two high-affinity, nonselective agonists (CP55,940 and AM12033). Interestingly, mutating the Y5.39 position impairs CB1 but not CB2 function. Conversely, mutating residue C6.47 improves CB1 but impairs CB2 signaling. The F7.35A mutation leads to a decrease in CP55,940 potency at CB1 and impairs internalization; however, AM12033 gains potency and promotes CB1 internalization. In CB2, mutation of F7.35A decreases the potency of CP55,940 and neither agonist induces internalization. These observations provide some insight into functional sensitivity of CB1 and CB2 to different agonists when conserved residues are mutated in the orthosteric pocket. [ABSTRACT FROM AUTHOR]

The cannabinoid receptors CB1 and CB2 mediate a variety of physiological processes and continue to be explored as desirable drug targets. Both receptors are activated by the endogenous endocannabinoids and the psychoactive components of marijuana. Over the years, many efforts have been made to make selective ligands; however, the high degree of homology between cannabinoid receptor subtypes introduces challenges in studying either receptor in isolation. Recent advancements in structure biology have resulted in a surge of high-resolution structures, enriching our knowledge and understanding of receptor structure and function. In this review, of recent cannabinoid receptor structures, key features of the inactive and active state CB1 and CB2 are presented. These structures will provide additional insight into the modulation and signaling mechanism of cannabinoid receptors CB1 and CB2 and aid in the development of future therapeutics. [ABSTRACT FROM AUTHOR]

Opioid analgesics such as morphine and fentanyl induce mu-opioid receptor (MOR)-mediated hyperactivity in mice. Herein, we show that morphine, fentanyl, SR-17018, and oliceridine have submaximal intrinsic efficacy in the mouse striatum using 35S-GTPγS binding assays. While all of the agonists act as partial agonists for stimulating G protein coupling in striatum, morphine, fentanyl, and oliceridine are fully efficacious in stimulating locomotor activity; meanwhile, the noncompetitive biased agonists SR-17018 and SR-15099 produce submaximal hyperactivity. Moreover, the combination of SR-17018 and morphine attenuates hyperactivity while antinociceptive efficacy is increased. The combination of oliceridine with morphine increases hyperactivity, which is maintained over time. These findings provide evidence that noncompetitive agonists at MOR can be used to suppress morphine-induced hyperactivity while enhancing antinociceptive efficacy; moreover, they demonstrate that intrinsic efficacy measured at the receptor level is not directly proportional to drug efficacy in the locomotor activity assay. [ABSTRACT FROM AUTHOR]

Actions of lubiprostone, a selective type-2 chloride channel activator, on mucosal secretion were investigated in guinea pig small intestine and colon. Flat-sheet preparations were mounted in Ussing flux chambers for recording short-circuit current ([I.sub.sc]) as a marker for electrogenic chloride secretion. Lubiprostone, applied to the small intestinal mucosa in eight concentrations ranging from 1-3000 nM, evoked increases in [I.sub.sc] in a concentration-dependent manner with an [EC.sub.50] of 42.5 nM. Lubiprostone applied to the mucosa of the colon in eight concentrations ranging from 1-3000 nM evoked increases in [I.sub.sc] in a concentration-dependent manner with an [EC.sub.50] of 31.7 nM. Blockade of enteric nerves by tetrodotoxin did not influence stimulation of [I.sub.sc] by lubiprostone. Antagonists acting at prostaglandin (PG)[E.sub.2], [EP.sub.1-3], or [EP.sub.4] receptors did not suppress stimulation of [I.sub.sc] by lubiprostone but suppressed or abolished [PGE.sub.2]-evoked responses. Substitution of gluconate for chloride abolished all responses to lubiprostone. The selective CFTR channel blocker, CFTR(inh)-172, did not suppress lubiprostone-evoked [I.sub.sc]. The broadly acting blocker, glibenclamide, suppressed (P < 0.001) lubiprostone-evoked [I.sub.sc]. Lubiprostone, in the presence of tetrodotoxin, enhanced carbachol-evoked [I.sub.sc]. The cholinergic component, but not the putative vasoactive intestinal peptide component, of neural responses to electrical field stimulation was enhanced by lubiprostone. Application of any of the prostaglandins, [E.sub.2], [F.sub.2], or [I.sub.2], evoked depolarization of the resting membrane potential in enteric neurons. Unlike the prostaglandins, lubiprostone did not alter the electrical behavior of enteric neurons. Exposure to the histamine [H.sub.2] receptor agonists increased basal [I.sub.sc] followed by persistent cyclical increases in [I.sub.sc]. Lubiprostone increased the peak amplitude of the dimaprit-evoked cycles. gastrointestinal tract; mucosal chloride secretion; enteric nervous system; prostaglandins; irritable bowel syndrome; cystic fibrosis transmembrane conductance regulator; CIC-2 channels

GPCRs modulate a plethora of physiological processes and mediate the effects of one‐third of FDA‐approved drugs. Depending on which ligand activates a receptor, it can engage different intracellular transducers. This 'biased signalling' paradigm requires that we now characterize physiological signalling not just by receptors but by ligand–receptor pairs. Ligands eliciting biased signalling may constitute better drugs with higher efficacy and fewer adverse effects. However, ligand bias is very complex, making reproducibility and description challenging. Here, we provide guidelines and terminology for any scientists to design and report ligand bias experiments. The guidelines will aid consistency and clarity, as the basic receptor research and drug discovery communities continue to advance our understanding and exploitation of ligand bias. Scientific insight, biosensors, and analytical methods are still evolving and should benefit from and contribute to the implementation of the guidelines, together improving translation from in vitro to disease‐relevant in vivo models. [ABSTRACT FROM AUTHOR]

Visual and auditory hallucinations accompany certain neuropsychiatric disorders, such as schizophrenia, and they also can be induced by the use or abuse of certain drugs. The heptahelical serotonin 2A receptors (5-HT2ARs) are molecular targets for drug-induced hallucinations. However, the cellular mechanisms by which the 5-HT2AR mediates these effects are not well understood. Drugs acting at the 5-HT2AR can trigger diverse signaling pathways that may be directed by the chemical properties of the drug. [beta]-arrestins are intracellular proteins that bind to heptahelical receptors and represent a point where such divergences in ligand-directed functional signaling could occur. Here we compare the endogenous agonist, serotonin, to a synthetic 5-HT2AR hallucinogenic agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI), in mice lacking [beta]-arrestin-2, as well as in cells lacking [beta]-arrestins. In mice, we find that serotonin induces a head twitch response by a [beta]-arrestin-2-dependent mechanism. However, DOI invokes the behavior independent of [beta]-arrestin-2. The two structurally distinct agonists elicit different signal transduction and trafficking patterns upon activation of 5-HT2AR, which hinge on the presence of [beta]-arrestins. Our study suggests that the 5-HT2AR-[beta]-arrestin interaction may be particularly important in receptor function in response to endogenous serotonin levels, which could have major implications in drug development for treating neuropsychiatric disorders such as depression and schizophrenia. 5-HT2A receptor | G protein-coupled receptor | internalization | MAP kinase | schizophrenia

Author(s): Tian Hua [1, 2, 3]; Kiran Vemuri [4]; Spyros P. Nikas [4]; Robert B. Laprairie [5]; Yiran Wu [1]; Lu Qu [1, 2, 3]; Mengchen Pu [1]; Anisha Korde [...]

Author(s): Laura M. Bohn [1]; Raul R. Gainetdinov [1]; Fang-Tsyr Lin [2]; Robert J. Lefkowitz [2]; Marc G. Caron (corresponding author) [1] Morphine is a powerful pain reliever, but also [...]