Dataset Information

Guanine nucleotide regulation of agonist binding to muscarinic cholinergic receptors. Relation to efficacy of agonists for stimulation of phosphoinositide breakdown and Ca2+ mobilization.

ABSTRACT: The efficacies of a series of six muscarinic cholinergic receptor agonists for stimulation of phosphoinositide breakdown and unidirectional efflux of 45Ca2+ in 1321N1 human astrocytoma cells were compared with the relative capacity of these agonists for formation of a GTP-sensitive high-affinity binding state in washed membranes. Carbachol and methacholine were 'full' agonists as regards phosphoinositide breakdown and Ca2+ mobilization, whereas bethanechol, arecoline and oxotremorine were 'partial' agonists for these two responses. Pilocarpine was the least efficacious of the six drugs tested. Except for pilocarpine, competition curves generated with the agonists and [3H]quinuclidinyl benzilate did not follow the Law of Mass Action for ligand interaction at a single site. Non-linear regression analyses of these data indicated that the data significantly better fit a two-, rather than a single-, site model with a high- and a low-affinity binding component. Competition curves generated in the presence of GTP were shifted to the right, and the extent of receptors in the high-affinity agonist-binding state was decreased. The relative efficacies of the six agonists for stimulation of phosphoinositide breakdown and Ca2+ mobilization were significantly correlated with the difference in affinities (KL/KH) between the two affinity states for each agonist. The relative efficacy of the agonists for stimulation of Ca2+ mobilization also was significantly correlated with the extent of receptors in the high-affinity state (%H) for each agonist. The results suggest that interaction with an as-yet unidentified guanine nucleotide regulatory protein is important in the mechanism whereby muscarinic receptors stimulate phosphoinositide breakdown in 1321N1 astrocytoma cells.

SUBMITTER: Evans T

PROVIDER: S-EPMC1152947 | biostudies-other | 1985 Dec

REPOSITORIES: biostudies-other

ACCESS DATA

Similar Datasets

Project description:BackgroundThe muscarinic receptor agonist xanomeline has antipsychotic properties and is devoid of dopamine receptor-blocking activity but causes cholinergic adverse events. Trospium is a peripherally restricted muscarinic receptor antagonist that reduces peripheral cholinergic effects of xanomeline. The efficacy and safety of combined xanomeline and trospium in patients with schizophrenia are unknown.MethodsIn this double-blind, phase 2 trial, we randomly assigned patients with schizophrenia in a 1:1 ratio to receive twice-daily xanomeline-trospium (increased to a maximum of 125 mg of xanomeline and 30 mg of trospium per dose) or placebo for 5 weeks. The primary end point was the change from baseline to week 5 in the total score on the Positive and Negative Syndrome Scale (PANSS; range, 30 to 210, with higher scores indicating more severe symptoms of schizophrenia). Secondary end points were the change in the PANSS positive symptom subscore, the score on the Clinical Global Impression-Severity (CGI-S) scale (range, 1 to 7, with higher scores indicating greater severity of illness), the change in the PANSS negative symptom subscore, the change in the PANSS Marder negative symptom subscore, and the percentage of patients with a response according to a CGI-S score of 1 or 2.ResultsA total of 182 patients were enrolled, with 90 assigned to receive xanomeline-trospium and 92 to receive placebo. The PANSS total score at baseline was 97.7 in the xanomeline-trospium group and 96.6 in the placebo group. The change from baseline to week 5 was -17.4 points with xanomeline-trospium and -5.9 points with placebo (least-squares mean difference, -11.6 points; 95% confidence interval, -16.1 to -7.1; P<0.001). The results for the secondary end points were significantly better in the xanomeline-trospium group than in the placebo group, with the exception of the percentage of patients with a CGI-S response. The most common adverse events in the xanomeline-trospium group were constipation, nausea, dry mouth, dyspepsia, and vomiting. The incidences of somnolence, weight gain, restlessness, and extrapyramidal symptoms were similar in the two groups.ConclusionsIn a 5-week trial, xanomeline-trospium resulted in a greater decrease in the PANSS total score than placebo but was associated with cholinergic and anticholinergic adverse events. Larger and longer trials are required to determine the efficacy and safety of xanomeline-trospium in patients with schizophrenia. (Funded by Karuna Therapeutics and the Wellcome Trust; ClinicalTrials.gov number, NCT03697252.).

Project description:UnlabelledCholinergic vulnerability, characterized by loss of acetylcholine (ACh), is one of the hallmarks of Alzheimer's disease (AD). Previous work has suggested that decreased ACh activity in AD may contribute to pathological changes through global alterations in alternative splicing. This occurs, at least partially, via the regulation of the expression of a critical protein family in RNA processing, heterogeneous nuclear ribonucleoprotein (hnRNP) A/B proteins. These proteins regulate several steps of RNA metabolism, including alternative splicing, RNA trafficking, miRNA export, and gene expression, providing multilevel surveillance in RNA functions. To investigate the mechanism by which cholinergic tone regulates hnRNPA2/B1 expression, we used a combination of genetic mouse models and in vivo and in vitro techniques. Decreasing cholinergic tone reduced levels of hnRNPA2/B1, whereas increasing cholinergic signaling in vivo increased expression of hnRNPA2/B1. This effect was not due to decreased hnRNPA2/B1 mRNA expression, increased aggregation, or degradation of the protein, but rather to decreased mRNA translation by nonsense-mediated decay regulation of translation. Cell culture and knock-out mice experiments demonstrated that M1 muscarinic signaling is critical for cholinergic control of hnRNPA2/B1 protein levels. Our experiments suggest an intricate regulation of hnRNPA2/B1 levels by cholinergic activity that interferes with alternative splicing in targeted neurons mimicking deficits found in AD.Significance statementIn Alzheimer's disease, degeneration of basal forebrain cholinergic neurons is an early event. These neurons communicate with target cells and regulate their long-term activity by poorly understood mechanisms. Recently, the splicing factor hnRNPA2/B, which is decreased in Alzheimer's disease, was implicated as a potential mediator of long-term cholinergic regulation. Here, we demonstrate a mechanism by which cholinergic signaling controls the translation of hnRNPA2/B1 mRNA by activation of M1 muscarinic type receptors. Loss of cholinergic activity can have profound effects in target cells by modulating hnRNPA2/B1 levels.

Dataset Information

Guanine nucleotide regulation of agonist binding to muscarinic cholinergic receptors. Relation to efficacy of agonists for stimulation of phosphoinositide breakdown and Ca2+ mobilization.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets