Co-localization of mu and delta opioid receptors on SK-N-SH cells detected by fluorescence microscopy using labeled anti-idiotypic antibodies. 
Selective fluorescence labeling of opioid receptor subclasses on SK-N-SH cultured cells has been accomplished using labeled polyclonal anti-idiotypic antibodies along with subclass-selective opioid agonists (DPDPE, delta-selective; DAMGO, mu-selective) as blocking reagents.  Labeling of the cells was examined using conventional fluorescence microscopy.  Co-localization of mu- and delta-opioid receptors on SK-N-SH cells has been studied by double labeling fluorescence experiments.  In agreement with our own, and other workers', previous observations on NG108-15 cells, a subpopulation of viable cells in asynchronous cultures are labeled.  Among those SK-N-SH cells that are labeled, both subclasses of receptors are seen.  On the basis of sequential blocking experiments we interpret our combined results to be consistent with a model where mu- and delta- binding sites reside on different subunits of a multimeric complex.