biostudies-literatureAlhosan NMedical Research Council969-987https://www.ebi.ac.uk/biostudies/studies/S-EPMC7618119biostudies-literatureUnknown182(4)<h4>Background and purpose</h4>Fentanyls and nitazenes are μ-opioid receptor agonists responsible for a large number of opioid overdose deaths. Here, we determined the potency, dissociation kinetics and antagonism by naloxone at the μ receptor of several fentanyl and nitazene analogues, compared to morphine and DAMGO.<h4>Experimental approach</h4>In vitro assays of G protein activation and signalling and arrestin recruitment were performed. AtT20 cells expressing μ receptors were loaded with a membrane potential dye and changes in fluorescence used to determine agonist potency, dissociation kinetics and susceptibility to antagonism by naloxone. BRET experiments were undertaken in HEK293T cells expressing μ receptors to assess Gi protein activation and β-arrestin 2 recruitment.<h4>Key resulBritish journal of pharmacologySlow dissociation kinetics of fentanyls and nitazenes correlates with reduced sensitivity to naloxone reversal at the μ-opioid receptor.PMC7618119MR/ S010890/1MR/S010890/1Kelly EHenderson GSantiago MAlhosan NCavallo DfalseSlow dissociation kinetics of fentanyls and nitazenes correlates with reduced sensitivity to naloxone reversal at the μ-opioid receptor.<h4>Background and purpose</h4>Fentanyls and nitazenes are μ-opioid receptor agonists responsible for a large number of opioid overdose deaths. Here, we determined the potency, dissociation kinetics and antagonism by naloxone at the μ receptor of several fentanyl and nitazene analogues, compared to morphine and DAMGO.<h4>Experimental approach</h4>In vitro assays of G protein activation and signalling and arrestin recruitment were performed. AtT20 cells expressing μ receptors were loaded with a membrane potential dye and changes in fluorescence used to determine agonist potency, dissociation kinetics and susceptibility to antagonism by naloxone. BRET experiments were undertaken in HEK293T cells expressing μ receptors to assess Gi protein activation and β-arrestin 2 recruitment.<h4>Key resul2025-01-01T00:00:00Z2025 Feb2026-06-01T06:32:38.357Z2026-04-08T10:02:43.716ZS-EPMC76181193943783310.1111/bph.17376