COMPARATIVE PHARMACOLOGICAL PROPERTIES AND FUNCTIONAL COUPLING OF MU-OPIOID AND DELTA-OPIOID RECEPTOR-SITES IN HUMAN NEUROBLASTOMA SH-SY5Y CELLS

  • 1 July 1987
    • journal article
    • research article
    • Vol. 32  (1) , 109-118
Abstract
The characteristics of .mu. and .delta. opioid receptor sites present in human neuroblastoma SH-SY5Y cells were investigated using [D-Ala2-N-methyl-Phe4-Gly-(01)5]enkephalin (DAGO) and [2-D-penicillamine, 5-D-penicillamine]enkephalin (DPDPE), which are the most selective radioligands available for .mu. and .delta. sites, respectively. Scatchard analysis of the saturation isotherms revealed high affinity binding to a single class of sites for both [3H] DAGO (.mu.) and [3H]DPDPE (.delta.). [3H]DAGO labeled twice the number of sites compared to the binding capacity of [3H]DPDPE, yielding a .mu./.delta. ratio of 2:1. Selective suppression of [3H]diprenorphine binding by specific opioid "blocking" ligands also showed a predominance of .mu. receptors, representing 65-70% of the total opioid sites. Competition binding studies carried out with a series of opiates and opioid peptides displayed higher potencies of .mu.-and .delta.-selective ligands in displacing the specific binding of [3H]DAGO and [3H]DPDPE, respectively. The [3H]diprenorphine/agonist competition curves were biphasic, indicating the high and low affinity states of .mu. and .delta. receptor sites in SH-SY5Y cells. Guanine nucleotide and sodium had differential effects on the agonist affinity and the proportion of high affinity states of .mu. and .delta. receptors. The .mu. and .delta. receptor sites were shown to be functionally coupled to adenylate cyclase. All of these data support the independent existence of .mu. and .delta. receptor types in human neuroblastoma cells. SH-SY5Y cells, therefore, represent a suitable model for investigating opioid-mediated responses in nerve cell populations.