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Updated: May 26, 2026

Tracking Drug-induced Changes in Receptor Post-internalization Trafficking by Colocalizational Analysis
Published on: July 3, 2015
Agonist-selective effects of opioid receptor ligands on cytosolic calcium concentration in rat striatal neurons
G Cristina Brailoiu1, Elena Deliu, Robert Hooper
1Department of Pharmacology, Temple University School of Medicine, Philadelphia, PA 19140, USA.
Background:
Buprenorphine is an opioid receptor ligand whose mechanism of action is incompletely understood.
Methods:
Using Ca(2+) imaging, we assessed the effects of buprenorphine, β-endorphin, and morphine on cytosolic Ca(2+) concentration [Ca(2+)](i), in rat striatal neurons.
Results:
Buprenorphine (0.01-1 microM) increased [Ca(2+)](i) in a dose-dependent manner in a subpopulation of rat striatal neurons. The effect of buprenorphine was largely reduced by naloxone, a non-selective opioid receptor antagonist, but not by micro, κ, δ or NOP-selective antagonists. β-Endorphin (0.1 microM) increased [Ca(2+)](i) with a lower amplitude and slower time course than buprenorphine. Similar to buprenorphine, the effect of β-endorphin was markedly decreased by naloxone, but not by opioid-selective antagonists. Morphine (0.1-10 microM), did not affect [Ca(2+)](i) in striatal neurons.
Conclusions:
Our results suggest that buprenorphine and β-endorphin act on a distinct type/subtype of plasmalemmal opioid receptors or activate intracellular opioid-like receptor(s) in rat striatal neurons.
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