SK‐N‐BE: A Human Neuroblastoma Cell Line Containing Two Subtypes of δ‐Opioid Receptors

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Abstract
A human neuroblastoma cell line, SK-N-BE, was shown to express a substantial amount of opioid receptors (200–300 fmol/mg of protein). A ligand binding profile of these receptors revealed that they could belong to two distinct subtypes of δ-opioid receptors. Results from sucrose-gradient sedimentation experiments were compared with similar data obtained with the μ-opioid receptor of the rabbit cerebellum and the δ-opioid receptor of the hybrid NG108–15 cell line and have shown that the opioid receptor of the SK-N-BE cell line behaved hydrodynamically as an intermediate between μ-and δ-opioid receptors. Taken together, pharmacological and hydrodynamic studies suggest that the opioid receptors present in the SK-N-BE cell membranes could belong to two δ-opioid receptor subtypes interacting allosterically. Functional experiments suggest that at least one of these subtypes of δ-opioid receptor is negatively coupled to the adenylate cyclase via a Gi protein and that the opiate receptors of the SK-N-BE neuroblastoma cell line undergo a rapid down-regulation when preincubated in the presence of the high-affinity opioid agonist, etorphine.