Receptor-mediated stimulation of brain GTPase by opiates in normal and dependent rats

doi:10.1016/0006-291X(84)90230-4

Biochemical and Biophysical Research Communications

Volume 121, Issue 2, 15 June 1984, Pages 641-648

https://doi.org/10.1016/0006-291X(84)90230-4 Get rights and content

Abstract

In membranes from rat brain striatum, opiate agonists stimulated low-K_m GTPase. Half-maximal enhancement of enzyme activity was obtained with 0.09 μM morphine and 3.8 μM levorphanol. This order of potency corresponded to that of the affinities of these compounds in binding to opiate receptor. The effect was inhibited by the antagonist naloxone. As shown by the use of the enantiomers levorphanol and dextrorphan, only the pharmacologically active stereoisomer stimulated GTPase. In membranes isolated from morphine-dependent rats, the activity of GTPase was reduced 20–40% relative to that in control rats. After the precipitation of morphine abstinence by naloxone, brain GTPase activity was intermediate between the respective values for naive and dependent animals.

References (16)

C.C. Barchfeld et al.
Life Sci
(1982)
G. Koski et al.
J. Biol. Chem
(1982)
O.H. Lowry et al.
J. Biol. Chem
(1951)
D. Cassel et al.
Biochim. Biophys. Acta
(1976)
M. Parenti et al.
Life Sci
(1983)
S.K. Sharma et al.
S.K. Sharma et al.
C.C. Barchfeld et al.
The Pharmacologist
(1981)

There are more references available in the full text version of this article.

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Agonist-induced high-affinity GTPase activity was investigated using the crude membrane preparation from rat striatum. High-affinity GTPase activity was stimulated by dopamine and carbachol in a Mg²⁺-dependent manner and with possible optimum NaCl concentrations of 50–100 mM to detect the percent increase induced by each agonist. Dopamine and selective (as well as non-selective) D₂ receptor agonists, but not selective D₁ receptor agonists, stimulated activity in a concentrationdependent manner, with affinities which were significantly correlated with those for adenylate cyclase inhibition as previously reported in the literature. Maximal percent stimulation above basal high-affinity GTPase activity was 9.8 ± 0.6% and 4.4–7.6% for dopamine and other synthetic dopamine D₂ receptor agonists, respectively. Dopamine-stimulated activity was inhibited by several dopamine receptor antagonists with the following rank order of potency: (+)-butaclamol > spiperone > raclopride > S(−)-sulpiride; but not by (−)-butaclamol or SCH 23390. High-affinity GTPase activity was also stimulated by carbachol and acetylcholine through the pirenzepine-insensitive muscarinic receptors. Preincubation of the membranes with $AS 7$ , a specific antiserum to G_i1 and G_i2, appeared to attenuate dopaminesensitive activity, suggesting that G_i1 and/or G_i2 may be at least partially involved. These results indicate that high-affinity GTPase activity in rat striatal membranes is activated through dopamine D₂-like receptors and pirenzepine-insensitive muscarinic receptors, both of which are negatively coupled to adenylate cyclase via G_i proteins.

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Receptor-mediated stimulation of brain GTPase by opiates in normal and dependent rats

Abstract

Life Sci

J. Biol. Chem

J. Biol. Chem

Biochim. Biophys. Acta

Life Sci

The Pharmacologist