Guanine Nucleotide and Cation Regulation of μ, δ, and k Opioid Receptor Binding: Evidence for Differential Postnatal Development in Rat Brain

Abstract

A study of the onset of cation and guanine nucleotide regulation of delta, mu, and kappa rat brain opioid receptors during postnatal development was undertaken. Site-specific binding assays were utilized for each receptor type and the effects of 0.5 mM MnCl2, 100 mM NaCl, and/or 50 microM guanosine-5'-(beta, gamma-imido) triphosphate [Gpp(NH)p] were assessed. The most pronounced changes of opioid binding were seen in the presence of Mn2+. In adults, agonist binding to delta sites was stimulated by Mn2+, whereas that to mu sites was not affected and kappa binding was inhibited. The postnatal development of Mn2+ regulation for the three receptor subtypes was distinctly different. The largest effects were seen on delta sites detected in the early neonatal period, Mn2+ eliciting a 68% stimulation of binding over controls at day 1. Significant inhibition of kappa site binding by Mn2+ was detected only after the third postnatal week. Mn2+ caused a significant reversal of Gpp(NH)p inhibition of delta binding in the early neonatal period, exceeding that in the absence of regulators. Inhibition of mu and delta receptor binding by Na+ was greater, and the Mn2+ reversal of this effect was smaller, in the first 2 postnatal weeks than in adults. Gpp(NH)p + Na+ regulation did not change appreciably during the postnatal period. However, Mn2+ reversal of the considerable inhibition elicited by the combination of Na+ and Gpp(HN)p was developmental time-dependent. The data are discussed in terms of multiple sites of interaction for guanine nucleotides and cations.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential coupling of opioid binding sites to guanosine triphosphate binding regulatory proteins in subcellular fractions of rat brain

“…Gpp(NH)p inhibited opioid agonist binding in SPM preparations similar to unfractionated membranes (Szucs et al, 1987, and references therein), whereas microsomes were relatively insensitive (Figs. l and 2).…”

“…1 . Modulation of p , 6, and K opioid receptor binding in SPM and microsomes by 50 pM Gpp(NH)p (G), 100 mM NaCl (Na), and/or 0.5 mM MnCI, (Mn (Szucs et al, 1987). Where appropriate, membranes (== 1 mg protein) in a Tris buffer containing protease inhibitors were treated with 1 % digitonin at 4°C for 30 min, then centrifuged at 100,OOOg for 1 hr to yield a solubilized preparation as described elsewhere (Simon et al, 1986).…”

“…In most cases, Naf and Gpp(NH)p inhibit opioid agonist binding in unfractionated membranes, whereas M + + reverses this effect. Recently, age-dependent differential effects of these agents on p, 6, and K opioid binding in unfractionated brain membranes have been described (Szucs et al, 1987, and .…”

Weaning‐induced development of δ‐opioid receptors in rat brain: differential effects of guanine nucleotides and sodium upon ligand‐receptor recognition

“…Much of the early opioid literature showed that δ‐receptors were regulated by guanine nucleotides and Na + (Blume, 1978; Pert & Snyder, 1974; Pfeiffer et al , 1982; Werling et al , 1984; Zajac & Roques, 1985) and that the loss of binding of agonist but not antagonists probably reflected uncoupling of the G‐protein from its receptor (Childers, 1991). Although the extent of the reduction of agonist binding for both GTP analogues and Na + varies (Chang et al , 1983; Puttfarken et al , 1986; Szucs et al , 1987) these differences have often been suggested to reflect differences in the experimental systems (Cox, 1993).…”