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Agonist Action at D 2(short) Dopamine Receptors Determined in Ligand Binding and Functional Assays
Author(s) -
Gardner B. R.,
Hall D. A.,
Strange P. G.
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.69062589.x
Subject(s) - agonist , quinpirole , partial agonist , apomorphine , chemistry , dopamine agonist , gtp' , endogenous agonist , spiperone , intrinsic activity , inverse agonist , dopamine receptor , endocrinology , medicine , receptor , pharmacology , biology , biochemistry , dopamine receptor d1 , enzyme
Mechanisms of agonist action at the G protein‐coupled D 2(short) dopamine receptor expressed in Chinese hamster ovary cells have been investigated. Agonist binding was assayed in the presence and absence of GTP (100 µ M ). Data in the absence of GTP were fitted best by a two‐site model (apomorphine, dopamine, 10,11‐dihydroxy‐ N‐n ‐propylnorapomorphine hydrochloride, and quinpirole) or a one‐site model [bromocriptine, dihydroergocristine, and (−)‐3‐(3‐hydroxyphenyl)‐ N ‐propylpiperidine hydrochloride], whereas in the presence of GTP a one‐site model was the best fit for all compounds. Agonist binding parameters were used to provide a measure of the ability of the agonist to stabilise the ternary complex of agonist/receptor/G protein. Agonist stimulation of [ 35 S]guanosine 5′‐ O ‐(3‐thiotriphosphate) ([ 35 S]‐GTPγS) binding for a range of agonist concentrations was measured and the EC 50 and maximal effects determined. The initial rates of [ 35 S]GTPγS binding induced by maximally stimulating agonist concentrations were also recorded. Simultaneous inhibition of agonist‐stimulated [ 35 S]GTPγS binding and receptor occupancy by spiperone was determined. Agonist inhibition of forskolin‐stimulated cyclic AMP accumulation was determined for a range of agonist concentrations and the EC 50 and maximal inhibition recorded. The data on the maximal agonist responses showed that it was possible to detect a spectrum of agonist efficacy (partial and full agonism) in both functional assays. The data on the apparent potencies of agonists to elicit the functional responses showed that different extents of amplification of response were seen for different agonists in both assays. The maximal activity data have been compared with the stabilisation of the agonist/receptor/G protein ternary complex as measured in binding assays.