Mechanism of agonist and antagonist binding to .alpha.2 adrenergic receptors: evidence for a precoupled receptor-guanine nucleotide protein complex

Biochemistry ◽  
1988 ◽  
Vol 27 (7) ◽  
pp. 2374-2384 ◽  
Author(s):  
Richard R. Neubig ◽  
Robin D. Gantzos ◽  
William J. Thomsen
Keyword(s):  
Protein Complex ◽  
Adrenergic Receptors ◽  
Guanine Nucleotide ◽  
Agonist And Antagonist ◽  
Antagonist Binding

Sodium and guanine nucleotide regulation of dopamine receptor agonist and antagonist binding sites in MtTW15 pituitary tumors

1988 ◽  
Vol 66 (2) ◽  
pp. 246-249 ◽  
Author(s):  
Thérèse Di Paolo ◽  
Daniel Lévesque
Keyword(s):  
Dopamine Receptor ◽  
Binding Sites ◽  
Pituitary Tumors ◽  
Lower Proportion ◽  
Dopamine Receptor Agonist ◽  
Guanine Nucleotide ◽  
Agonist And Antagonist ◽  
Nucleotide Regulation ◽  
Antagonist Binding ◽  
Agonist Affinity States

The modulation of the dopamine receptor in MtTW15 tumors was investigated. The antagonist dopaminergic binding site in MtTW15 tumors labelled with [3H]spiperone remains unchanged at 25 °C in the presence or absence of sodium or guanine nucleotides (Gpp(NH)p); by contrast at 37 °C sodium increases the affinity while Gpp(NH)p decreases it slightly. The dopamine receptor in this tumor, such as the intact adenohypophysis, exists in a high and low affinity state for dopamine agonists. These agonist affinity states evaluated with apomorphine competition for [3H]spiperone binding show similar affinities as those of intact tissue but have a lower proportion of the high affinity state. At 25 °C, a partial conversion of the high into the low affinity state is obtained in the presence of both sodium and Gpp(NH)p, while at 37 °C a complete conversion is observed. These data show differences in the modulation of antagonist and agonist dopaminergic binding sites in MtTW15 pituitary tumors compared with the intact pituitary.

Effect of exercise duration on density and coupling of beta-adrenergic receptors on human mononuclear cells

1989 ◽  
Vol 66 (3) ◽  
pp. 1494-1500 ◽  
Author(s):  
M. J. Frey ◽  
D. Mancini ◽  
D. Fischberg ◽  
J. R. Wilson ◽  
P. B. Molinoff
Keyword(s):  
Heart Rate ◽  
Adrenergic Receptors ◽  
Regulatory Protein ◽  
Nucleotide Binding ◽  
Plasma Norepinephrine ◽  
Base Line ◽  
Guanine Nucleotide ◽  
Beta Adrenergic Receptors ◽  
Beta Adrenergic ◽  
Guanine Nucleotide Binding

The effect of maximal exercise on lymphocyte beta-adrenergic receptors was examined in 26 normal subjects. Exercise increased O2 consumption (Vo2) from 5 +/- 1 to 50 +/- 4 ml.min-1.kg-1, plasma norepinephrine level from 188 +/- 28 to 2,682 +/- 160 pg/ml, and plasma epinephrine level from 94 +/- 72 to 857 +/- 180 pg/ml. The density of beta-adrenergic receptors on lymphocytes obtained at rest was 31 +/- 3.7 fmol/mg protein; exercise increased the density of receptors by 86 +/- 33% (range 0–257%) to 58.3 +/- 1.5 fmol/mg protein but did not alter the affinity of the receptor for [125I]iodopindolol or the coupling of the receptor to the guanine nucleotide-binding regulatory protein. The density of beta-adrenergic receptors increased progressively throughout exercise and paralleled the increase in heart rate. The magnitude of the change in the density of beta-adrenergic receptors did not correlate with the magnitude of the increase in heart rate, Vo2, or plasma levels of catecholamines. The density of receptors was still elevated 15 min after completion of exercise but fell below base line 1 h after peak exercise to 18.2 +/- 6.7 fmol/mg protein (P less than 0.05 vs. base-line levels). These results demonstrate that exhaustive exercise results in a progressive increase in the number of beta-adrenergic receptors on lymphocyte membranes, followed by a reduction in the density of receptors during the recovery phase of exercise. Despite a significant increase in the level of plasma catecholamines, the receptor remains coupled to the guanine nucleotide-binding regulatory protein.

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