Guanine nucleotide-induced enhancement of affinity of dopaminergic membrane receptors of nerve tissues ofLymnaea stagnalis for agonists

• DOI: 10.1007/bf01054257
• Publication Date: 2005-01-28T11:35:12Z
• Authors: I. M. Prudnikov
• Keywords: Spiperone; EGTA; Lymnaea stagnalis

Reception of labeled dopamine [7,83H] DA (hereafter, DA) and of a D1 receptor agonist, [3H] SKF 38393, in membranes from nerve tissues of the fresh-water lunged mollusc,Lymnaea stagnalis, was investigated. The presence of 10−6 to 10−5 M of guanine di- and triphosphate as well as of their nonhydrolizable analogs amplified the binding of agonists to membrane DA receptors, especially after EGTA addition. Replacement of EGTA with EDTA partly suppressed the binding amplification effect. Higher concentrations of guanine nucleotides (10−3 to 10−4 M) inhibited the binding of DA and of its agonists. The GDPβS-dependent stimulation of agonist binding was found not to be induced by subunits of GTP-binding proteins (G proteins), immunologically similar to β1-, β2-, and Goα-subunits of G protein in vertebrates. Membrane phosphorylation by a catalytic subunit of cAMP-dependent protein kinase fully inhibited the stimulating effect of guanine nucleotides on the agonist binding to DA receptors and markedly depressed the DA-dependent GTPase activity.