Two subpopulations of α1-adrenergic receptors with high and low affinity for agonists: Short-term exposure to agonists reduced the high-affinity sites

Fratelli, Maddalena; Marasco, Onorina; Blasi, Antonio De

doi:10.1016/0167-4889(87)90159-5

Cited by 8 publications

(3 citation statements)

References 12 publications

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“…The decreases in [3H]prazosin binding to plasma membranes following pretreatment of hepatocytes with phenylephrine or vasopressin are consistent with observations in DDT1 MF-2 smooth muscle cells, in which agonists decreased cell surface a,adrenergic receptors, as indicated by the binding of [3H]prazosin to intact cells at 4 °C (Fratelli et al, 1987;Colucci et al, 1988;Cowlen and Toews, 1988). However, while the present study shows that PMA markedly decreases hepatocyte plasma membrane al-adrenergic receptors, and also in livers perfused with PMA (Lynch et al, 1985a), it appears that in DDT1 MF-2 cells PMA itself does not decrease plasma membrane al-adrenergic receptors (Colucci et al, 1988;Cowlen and Toews, 1988), although PMA has potentiated the agonist-induced decrease in a1-adrenergic receptors (Cowlen and Toews, 1988).…”

Section: Discussionsupporting

confidence: 85%

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Beeler

Cooper

1995

Biochemical Journal

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The effect of phorbol 12-myristate 13-acetate (PMA) on hepatocyte alpha 1-adrenergic receptors was determined by [3H]prazosin binding to plasma membranes from control and PMA-treated hepatocytes. Membranes from hepatocytes incubated with PMA (1 microgram/ml) for 1 h exhibited a 40% decrease in alpha 1-adrenergic receptors (481 +/- 10 fmol/mg of protein; mean +/- S.E.M. for three separate experiments) relative to vehicle-treated (dimethylformamide) hepatocytes (802 +/- 91 fmol/mg of protein; n = 3), with no significant effect on the KD. The PMA-induced decrease in alpha 1-adrenergic receptors was maximal by 30 min and half-maximal inhibition of [3H]prazosin binding occurred with a PMA concentration of approx. 15 ng/ml. Pretreatment of hepatocytes with staurosporine (5 microM) blocked the effect of PMA, and 4 beta-phorbol 13-monoacetate was ineffective, suggesting the involvement of protein kinase C (PKC). Treatment of hepatocytes with primaquine (300 microM) for 15 min decreased hepatocyte plasma membrane alpha 1-adrenergic receptors by 34.0 +/- 2.4% (mean +/- S.E.M. of three experiments). Removal of primaquine allowed essentially complete recovery (98 +/- 4%; mean +/- S.E.M. for five separate experiments) of plasma membrane [3H]prazosin binding within 20 min, suggesting that the alpha 1-adrenergic receptor undergoes endocytotic recycling. Addition of PMA (1 microgram/ml) to hepatocytes immediately after removal of primaquine, completely inhibited the increase in plasma membrane alpha 1-adrenergic receptors relative to control cells, but had no effect on hepatocytes whose cell surface alpha 1-receptors remaining after primaquine treatment had been inactivated by alkylation. These observations suggested that activation of PKC may facilitate the internalization of the alpha 1-adrenergic receptor in hepatocytes.

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Section: Discussionsupporting

confidence: 85%

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Beeler

Cooper

1995

Biochemical Journal

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“…Their binding properties in cerebral cortex were shown to be similar to those in smooth muscle (Minneman, 1983). Subsequently, on the basis of work carried out on slices, membrane preparations or cultured cells, evidence has accumulated for existence of two subtypes or sites of a,-adrenoreceptors in rat cerebral cortex with different sensitivities to inactivation by the site-directed alkylating agent chloroethylclonidine (CEC), different affinities for the competitive antagonists WBAlOl and benoxanthian and linked to different mechanisms for signal transduction (Fratelli et al, 1987;Michel et al, 1990;Minneman et al, 1988;Morrow and Creese, 1986;Wilson and Minneman, 1989;Wilson et al, 1990). The high-affinity a,-adrenergic receptor, insensitive to CEC and not linked to the phosphoinositol transduction sys- tem, has been designated a,*, while the low-affinity, CEC-sensitive, and phosphoinositol hydrolysis-coupled receptor subtype the a,,.…”

Section: Discussionmentioning

confidence: 99%

Bi‐affinity α₁‐adrenoceptor binding in normal rat brain in vivo

Gjedde¹,

Dyve²,

Yang³

et al. 1991

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The specific binding in rat brain in vivo of [125I]HEAT ([125I]iodo-2-[beta-(4-hydroxyphenyl)ethylamino methyl), a selective alpha 1-adrenoceptor ligand, was analyzed by a method designed to distinguish sites with different affinities. The data indicate at least two sites with different affinities for the alpha 1-adrenoreceptor in normal rat brain in vivo: a high-affinity site with Kd (half-saturation constant) of 3.6 +/- 0.7 nM (AV +/- SD), and a low-affinity site with Kd of 668 +/- 552 nM. The density (Bmax) of the high-affinity site in nine brain regions--auditory, visual, sensorimotor (four layers) and frontal cortex and lateral thalamic and medial geniculate nuclei--varied from 2.2 +/- 0.8 to 14.6 +/- 0.6 pmole/g, while the low-affinity range was 149 +/- 44 to 577 +/- 30 pmole/g. The results also revealed a very dynamic relationship between the two sites regulated by the concentration of the ligand ranging from 80% preponderance of the high-affinity sites at low ligand concentrations to more than 95% preponderance of the low-affinity sites at high ligand concentrations.

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“…Increasing amounts of unlabeled ligand did not displace the binding of [1251]HEAT in this region. This finding suggested that the ligand either associated with receptors other than the a,subtype, or that a,-receptors may exist in at least two affinity states or subtypes (Fratelli et al, 1987). This possibility may also explain why the same tissue preparations can yield different B,, values when structurally different ligands are used.…”

Section: Equilibrium Analysismentioning

confidence: 98%

In vivo quantification of blood‐brain transfer and binding of [¹²⁵I]HEAT, an α₁‐adrenoceptor antagonist

Dyve

Gjedde

Dikšić

et al. 1989

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The uptake and binding constants of [125I]iodo-2-[beta-(4-hydroxyphenyl)-ethyl-amino-methyl]tetralone ( [125I]HEAT) in rat brain were determined in vivo. The initial clearance of the radioligand from blood to brain, K1, was calculated from the initial uptake of the radioligand; it averaged 0.21 +/- 0.01 (SD) ml g-1 min -1, consistent with an initial extraction of 25% (i.e., one-quarter of the blood flow). The most strongly binding regions included the olfactory bulb, thalamic nuclei, medial geniculate body, and cerebral cortical layers. We identified saturable, specific binding in frontal cortex layers 1, 5a, and 5c (motor region), frontal cortex layers 3+4, ventral thalamic nuclei, medial geniculate body, striatum, cerebellum, and olfactory bulb. Addition of unlabeled ligand depressed binding in all regions to the same low level (partition coefficient) of 0.8 ml g-1. Displacement of [125 I]HEAT binding by unlabeled HEAT yielded a global affinity constant (KDVd) of 34 +/- 8 pmol g-1 and receptor densities (Bmax) that varied from 50 pmol g-1 in cerebellar cortex and caudate nucleus to 200 pmol g-1 in the region of highest specific binding, the medial geniculate body.

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Two subpopulations of α1-adrenergic receptors with high and low affinity for agonists: Short-term exposure to agonists reduced the high-affinity sites

Cited by 8 publications

References 12 publications

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Bi‐affinity α₁‐adrenoceptor binding in normal rat brain in vivo

In vivo quantification of blood‐brain transfer and binding of [¹²⁵I]HEAT, an α₁‐adrenoceptor antagonist

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Two subpopulations of α1-adrenergic receptors with high and low affinity for agonists: Short-term exposure to agonists reduced the high-affinity sites

Cited by 8 publications

References 12 publications

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Regulation of hepatocyte plasma membrane α1-adrenergic receptors by 4β-phorbol 12-myristate 13-acetate

Bi‐affinity α1‐adrenoceptor binding in normal rat brain in vivo

In vivo quantification of blood‐brain transfer and binding of [125I]HEAT, an α1‐adrenoceptor antagonist

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Product

Resources

About

Bi‐affinity α₁‐adrenoceptor binding in normal rat brain in vivo

In vivo quantification of blood‐brain transfer and binding of [¹²⁵I]HEAT, an α₁‐adrenoceptor antagonist