ISSN:
1573-6830
Keywords:
morphine (µ) receptor conformation
;
enkephalin (δ) receptor conformation
;
allosteric effectors
;
sulfhydryl reagents
;
Type 1 opiate receptor
;
striatal patches
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Summary 1. The aim of this study was to determine the effects of sulfhydryl and disulfide modifiers on the ability of ions to change theµ/δ-ligand selectivity of opiate receptors of rat striatal sections. 2. At 25°C, Na+ and Na+ + Mn2+ promote formation of theδ-state at the expense ofµ-states since Na+ enhances [D-Ala2, D-Leu5]enkephalin (D-ENK) binding while inhibiting dihydromorphine (DHM); Mn2+ + Na+ synergistically enhances D-ENK binding, while Mn2+ reverses Na+ inhibition of DHM; and Na+ has no effect on naloxone (NAL) binding at this temperature. 3. Alkylation of a receptor—SH group(s) by NEM results in a decreased ability to assume theδ-state, and theµ-antagonist state is preferentially induced by Na+ since Na+ enhancement of D-ENK binding is converted to marked inhibition, Na+ inhibition of DHM is enhanced, synergistic stimulation of D-ENK binding by Mn2+ + Na+ and the ability of Mn2+ to counteract Na+ inhibition of DHM are both lost, and Na+ becomes markedly stimulatory on naloxone binding at 25°C. 4. Oxidation of receptor—SH to disulfide results in a decreased ability to assume theδ-state, and theµ-states are preferentially induced by ions since Na+ enhancement of D-ENK binding is lost, Na+ inhibition of DHM binding is enhanced, and the ability of Mn2+ to counteract Na+ inhibition of DHM is diminished. 5. An intact disulfide bridge is indicated in stabilization of theµ-states while reduced sulfhydryl groups are indicated in stabilization of theδ-state, since receptor reduction by dithiothreitol (DTT) enhances D-ENK binding while inhibiting DHM and receptor oxidation by H2O2 impartsµ-like ionic responses. 6. Sulfhydryl-disulfide redox or exchange is a feasible mechanism ofµ/δ regulation since effects of receptor oxidation are reversed by reduction with DTT. 7. NEM and H2O2 inhibitµ andδ binding similarly, probably via a —SH at the ligand binding site.Differential effects of these agents are revealed only when effects of ions are studied. Therefore, the critical sulfhydryl/disulfide(s) involved inµ/δ conformational interconversion is possibly located some distance from the ligand binding site, at an allosteric site. 8. These data indicate that ionic effectors reciprocally regulateµ- andδ-ligand binding by inducing conformational changes in the receptor and support the suggestion that the Type 1 opiate receptor of rat striatal patches consists of an equilibrium of “µ-conformation” and “δ-conformation” states.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00711077
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