Protein secretion in lacrimal gland: alpha 1-beta-adrenergic synergism

1986 ◽  
Vol 250 (5) ◽  
pp. C704-C712 ◽  
Author(s):  
P. Mauduit ◽  
G. Herman ◽  
B. Rossignol
Keyword(s):  
Binding Sites ◽  
Adrenergic Receptors ◽  
Specific Binding ◽  
Secretory Response ◽  
Receptor Subtype ◽  
Beta Adrenergic ◽  
Homogeneous Population ◽  
Specific Binding Sites ◽  
Adrenergic Antagonist ◽  
Simultaneous Activation

We have shown the existence of a homogeneous population of specific binding sites for [3H]prazosin in membranes from rat lacrimal glands. The value of the equilibrium dissociation constant was 0.186 +/- 0.07 nM, and the density of specific binding sites was 20.4 +/- 1 fmol/mg protein. Taking into account the potency sequences for adrenergic agonists and antagonists for competition with these [3H]prazosin binding sites, we identified them as alpha 1-adrenergic receptors. Moreover, we have demonstrated that the stimulation of protein discharge evoked by epinephrine could be partly attributed to the occupation of this alpha-adrenergic receptor subtype. However, the inhibition pattern of the epinephrine effect by a beta-adrenergic antagonist, 1-propranolol, and the characteristics of the secretory response observed when selectively stimulating the alpha 1- and beta-adrenergic receptors, either separately or simultaneously, suggest that 1) a simultaneous activation of both receptors is necessary to produce a maximal secretory response to catecholamines; and 2) a synergism may exist between these two routes of stimulation, leading to an amount of protein discharge higher than that expected in the case of additive effects.

Increased beta-adrenergic receptors in brown fat of winter-acclimatized Alaskan voles

1983 ◽  
Vol 245 (3) ◽  
pp. R357-R363 ◽  
Author(s):  
D. D. Feist
Keyword(s):  
Cold Acclimation ◽  
Binding Sites ◽  
Adrenergic Receptors ◽  
Specific Binding ◽  
Brown Fat ◽  
Scatchard Analysis ◽  
Beta Adrenergic Receptors ◽  
Hormonal Stimulation ◽  
Beta Adrenergic ◽  
Specific Binding Sites

To assess a possible mechanism for the enhanced thermogenesis of cold-acclimated and winter-acclimatized red-backed voles (Clethrionomys rutilus), beta-adrenergic receptors of brown fat were characterized by specific binding of (-)-[3H]-dihydroalprenolol [( 3H]DHA) to isolated brown fat membranes from 23 degrees C-acclimated controls, cold-acclimated (5 wk or 5 mo at 5 degrees C), wild summer, and winter-acclimatized voles. Scatchard analysis to determine the equilibrium dissociation constant (Kd) and the maximum number of binding sites (Bmax) for control brown fat membranes gave a Kd of 4.45 nM [3H]DHA and Bmax of 249 fmol [3H]DHA bound per milligram of protein. beta-Adrenergic agonists competed for specific binding sites with an order of potency typical of the beta 1 subtype of adrenergic receptors: (-)-isoproterenol greater than (-)-norepinephrine greater than or equal to (-)-epinephrine. After cold acclimation for 5 wk or 5 mo, the Kd and Bmax for adrenergic binding sites were similar to those of controls. Brown fat mass was 1.5 times greater than that of controls after 5 wk cold acclimation but similar to controls after 5 mo cold acclimation. Winter voles had 1.7 times higher Bmax and 1.6 times more brown fat than summer voles. Thus seasonal acclimatization to winter in red-backed voles appears to involve an increase in beta-adrenergic receptors in brown fat, but cold acclimation does not. The results suggest quantitative and possibly qualitative differences in neural and hormonal stimulation of brown fat between cold acclimation and winter acclimatization in voles.

scholarly journals Localization of β-adrenergic receptors in A431 cells in situ. Effect of chronic exposure to agonist

1989 ◽  
Vol 263 (2) ◽  
pp. 533-538 ◽  
Author(s):  
H Y Wang ◽  
M Berrios ◽  
C C Malbon
Keyword(s):  
Adrenergic Receptors ◽  
High Speed ◽  
Radioligand Binding ◽  
Specific Binding ◽  
Polyacrylamide Gel Electrophoresis ◽  
Beta Adrenergic Receptors ◽  
A431 Cells ◽  
Beta Adrenergic ◽  
Adrenergic Antagonist

The status of beta-adrenergic receptors was investigated in A431 cells exposed to chronic stimulation by the beta-adrenergic agonist, (-)-isoproterenol. Specific binding of beta-adrenergic antagonist (-)-[125I]iodocyanopindolol declined to 60-80% below control values within 12 h of agonist treatment. This decline in ligand binding was also observed in high-speed membrane fractions prepared from agonist-treated cells. Immunoblots probed with anti-receptor antibodies revealed both that beta-adrenergic receptors from untreated and treated cells migrated as 65,000-Mr peptides and that the cellular complement of receptor was unchanged. Indirect immunofluorescence localization of beta-adrenergic receptors was comparable in control (untreated) cells and cells challenged with (-)-isoproterenol for 1, 12, or 24 h. Thus receptor complement, migration on SDS/polyacrylamide-gel electrophoresis, and localization in situ are largely unaffected by agonist stimulation. Receptor binding of antagonist radioligands, in contrast, is markedly down-regulated in cells stimulated chronically with beta-adrenergic agonists. These data argue in favour of agonist-induced alteration(s) in the conformation of the receptor that preclude radioligand binding rather than agonist-induced receptor sequestration and/or degradation.

Hormonal regulation of hepatic glycogenolysis in the carp, Cyprinus carpio

1987 ◽  
Vol 252 (4) ◽  
pp. R653-R660 ◽  
Author(s):  
P. A. Janssens ◽  
P. Lowrey
Keyword(s):  
Cyprinus Carpio ◽  
Hormonal Regulation ◽  
Adrenergic Receptors ◽  
Specific Binding ◽  
Arginine Vasotocin ◽  
Dependent Manner ◽  
Beta Adrenergic ◽  
Alpha Adrenergic Receptors ◽  
Adrenergic Antagonist ◽  
Carp Cyprinus Carpio

Carp (Cyprinus carpio) liver maintained normal glycogen content and enzyme complement for several days in organ culture. Epinephrine-stimulated glycogenolysis, phosphorylase activation, and cyclic AMP (cAMP) accumulation in a concentration-dependent manner with EC50s of 100, 100, and 500 nM, respectively. These actions were blocked by the beta-adrenergic antagonist, propranolol, but not by the alpha-adrenergic antagonist phentolamine. Glycogenolysis and tissue cAMP were uninfluenced by 10(-6) M arginine vasotocin, arginine vasopressin, lysine vasotocin, lysine vasopressin, mesotocin, or oxytocin, but were slightly increased by 10(-5) M isotocin and slightly decreased by 10(-6) M angiotensin II. [125I]-iodocyanopindolol (ICP), a beta-adrenergic ligand, bound to isolated carp liver membranes with a KD of 83 pM. Maximum binding of 45 fmol/mg protein was at 600 pM. Propranolol, isoprenaline, epinephrine, phenylephrine, norepinephrine, and phenoxybenzamine displaced ICP with KDs of 100 nM, 2, 20, 20, 60, and 200 microM, respectively. The alpha-adrenergic antagonists, yohimbine and prazosin, showed no specific binding. These data provide evidence that catecholamines act via beta-adrenergic receptors in carp liver and that alpha-adrenergic receptors are not present. Vasoactive peptides play no significant role in regulation of carp liver glycogenolysis.

Alpha-adrenergic regulation of secretion by tracheal glands

1990 ◽  
Vol 259 (4) ◽  
pp. L198-L205 ◽  
Author(s):  
D. J. Culp ◽  
R. K. McBride ◽  
L. A. Graham ◽  
M. G. Marin
Keyword(s):  
Adrenergic Receptors ◽  
Specific Binding ◽  
Receptor Subtypes ◽  
Adrenergic Agonists ◽  
Beta Adrenergic ◽  
Adrenergic Regulation ◽  
Binding Characteristics ◽  
Low Concentrations ◽  
Adrenergic Antagonist ◽  
Uk 14,304

The purpose of the present study was to begin to characterize, pharmacologically, the alpha-adrenergic regulation of glycoconjugate secretion from airway glands. Using isolated gland cells from cat trachea, we determined the binding characteristics of [3H]dihydroergocryptine ([3H]DHE), an alpha-adrenergic antagonist, with equal affinities for alpha 1- and alpha 2-adrenergic receptors. Specific binding of [3H]DHE to gland cell homogenates was saturable, of high affinity (KDapp = 4.2 nM) and inhibited with greater efficacy by epinephrine much greater than isoproterenol. Competition experiments with alpha 1- and alpha 2-adrenergic selective antagonists (prazosin and yohimbine, respectively) demonstrated high- and low-affinity sites for each antagonist, indicating the presence of both receptor subtypes. In studies of glycoconjugate secretion by cat tracheal explants, secretion was stimulated by adrenergic agonists with the rank potency: norepinephrine greater than or equal to phenylephrine greater than epinephrine much greater than clonidine. alpha-Adrenergic-stimulated secretion (epinephrine + propranolol) was inhibited by low concentrations of prazosin, but was unaffected by 100 nM yohimbine. The alpha 2-adrenergic agonists, clonidine and UK-14,304, each markedly inhibited beta-adrenergic-stimulated secretion. Collectively, these results demonstrate alpha 1-adrenergic regulation of glandular glycoconjugate secretion and suggest alpha 2-adrenergic receptors may modulate beta-adrenergic-stimulated secretion.

Baboon erythrocyte ghosts contain beta-adrenergic receptors

1985 ◽  
Vol 249 (1) ◽  
pp. C15-C19 ◽  
Author(s):  
E. E. Susanni ◽  
F. P. Ross ◽  
D. R. Scriven ◽  
C. Rosendorff
Keyword(s):  
Binding Sites ◽  
Adrenergic Receptors ◽  
Dependent Manner ◽  
Erythrocyte Ghosts ◽  
Beta Adrenergic Receptors ◽  
Concentration Dependent Manner ◽  
Apparent Dissociation Constant ◽  
Beta Adrenergic ◽  
Adrenergic Antagonist ◽  
Number Of Binding Sites

We have used the beta-adrenergic antagonist [3H]dihydroalprenolol [( 3H]DHA) to identify binding sites on the erythrocyte membrane of the primate Papio ursinus. Analysis of the saturation isotherm revealed binding to be saturable with a maximal number of binding sites of 499 fmol/mg protein. [3H]DHA binds specifically to the erythrocyte ghosts with an apparent dissociation constant (Kd) of 0.57 +/- 0.06 nM. A similar value for Kd (0.46 +/- 0.07 nM) was evaluated from the rate constants of association (0.013 +/- 0.003 X nM-1 X min-1) and dissociation (0.006 +/- 0.001 X min-1). beta-adrenergic agonists compete for the binding sites with an order of potency (dl-isoproterenol greater than l-epinephrine greater than l-norepinephrine) typical of a beta 2-adrenergic receptor. Binding was shown to be stereospecific with l-stereoisomers being more potent than their corresponding d-stereoisomers in causing half-maximal inhibition. Isoproterenol stimulated the production of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) in a concentration-dependent manner, maximal levels (1.130 +/- 0.358 pmol cAMP/10(8) cells) being four times the basal levels. The results demonstrate the existence of a large number of beta-adrenergic receptors on baboon erythrocyte ghosts.

Decreased α-Adrenergic Receptors in Newborn Platelets: Cause of Abnormal Response to Epinephrine?

1979 ◽  
Author(s):  
Donald G. Corby ◽  
T.P. O’Barr
Keyword(s):  
Binding Sites ◽  
Adrenergic Receptors ◽  
Specific Binding ◽  
Platelet Rich Plasma ◽  
Newborn Infants ◽  
Adenosine Diphosphate ◽  
Scatchard Analysis ◽  
Single Class ◽  
Adrenergic Antagonist ◽  
Induced Aggregation

Platelets of newborn infants (NBP) fail to aggregate or release adenosine diphosphate in response to epinephrine (E). Because E-induced aggregation is an α-adrenergic event, we considered the possibility that NBP possess fewer E receptors than do those of adults. Therefore we compared the specific binding of the α-adrenergic antagonist, 3H-Dihydroergocryptine (DHE), in intact washed platelets prepared from paired samples of maternal and cord platelet rich plasma. NBP demonstrated normal kinetics of 3H -DHE binding and normal affinity for 3H-DHE. Scatchard analysis of 3H-DHE binding indicated a single class of binding sites that exhibited a high affinity for the radioligand (Kd = 7.5nM). Maternal platelets (MP) were found to bind approximately 2-fold more DHE than NBP (3.70 + 0.28 vs. 1.7 fmol/107 platelets) at saturation. This corresponds to 223 ± 17 vs. 105 ± II binding sites per platelet (p < 0.001). Repeat washing of NBP did not yield increased DHE binding suggesting the binding sites had not previously been masked by elevated circulating levels of E and/or nor-E in venous cord blood. When control platelets were incubated with concentrations of 3H-DHE that half-saturated the α-adrenergic receptors, diminution of platelet function comparable to that seen in HBP was observed. Since NBP and MP are similar size, it appears that a deficiency of α-adrenergic receptors may account for the diminished response of NBP to epinephrine.

scholarly journals Specific Binding of Rubidium in Chlorella

1962 ◽  
Vol 45 (5) ◽  
pp. 959-977 ◽  
Author(s):  
Dan Cohen
Keyword(s):  
Active Transport ◽  
Binding Sites ◽  
Specific Binding ◽  
High Concentration ◽  
External Concentration ◽  
Specific Binding Sites ◽  
Dense Suspension ◽  
Concentration Of Ions ◽  
The Individual ◽  
A Site

Specific binding sites for potassium, which may be components of the carriers for active transport for K in Chlorella, were characterized by their capacity to bind rubidium. A dense suspension was allowed to take up Rb86 from a low concentration of Rb86 and a high concentration of ions which saturate non-specific sites. The amount bound was derived from the increase in the external concentration of Rb86 following addition of excess potassium. The sites were heterogeneous. The average affinity of Rb and various other ions for the sites was determined by plotting the degree of displacement of Rb86 against log molar concentration of the individual ions. Interpolation gave the concentration for 50 per cent displacement of Rb, which is inversely related to affinity. The order of affinity was not changed when the cells were frozen, or boiled either in water or in 70 per cent ethanol. The affinity is maximal for ions with a crystalline radius of 1.3 to 1.5 A and a high polarizability, and is not related to the hydrated radius or valency. It is suggested that binding groups in a site are rigidly arranged, the irregular space between them being 2.6 to 3.0 A across, so that affinity is high for ions of this diameter and high polarizability.

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