PGE2 binding sites and PG-stimulated cyclic AMP accumulation in rat isolated glomeruli and glomerular cultured cells

1983 ◽  
Vol 30 (2) ◽  
pp. 201-214 ◽  
Author(s):  
Gérard Friedlander ◽  
Dominique Chansel ◽  
Josée Sraer ◽  
Marcelle Bens ◽  
Raymond Ardaillou
Keyword(s):  
Cyclic Amp ◽  
Binding Sites ◽  
Cultured Cells ◽  
Isolated Glomeruli ◽  
Cyclic Amp Accumulation

Coexistence of novel amylin-binding sites with calcitonin receptors in human breast carcinoma MCF-7 cells

1997 ◽  
Vol 155 (3) ◽  
pp. 423-431 ◽  
Author(s):  
U Zimmermann ◽  
B Fluehmann ◽  
W Born ◽  
JA Fischer ◽  
R Muff
Keyword(s):  
Breast Carcinoma ◽  
Cyclic Amp ◽  
Binding Sites ◽  
Human Breast Carcinoma ◽  
Human Breast ◽  
T47d Cells ◽  
Amino Terminal ◽  
Cyclic Amp Accumulation ◽  
Human Amylin ◽  
Mcf 7

Amylin, calcitonin (CT) and calcitonin gene-related peptide (CGRP) share limited structural homology including amino-terminal ring structures linked by a disulfide bridge and amidated carboxy-termini. Here, we have compared [125I]Bolton-Hunter-[Lys1] rat amylin ([125I]amylin) binding and the stimulation of cyclic AMP accumulation by human (h) amylin, hCT and hCGRP-I in the human breast carcinoma cell lines MCF-7 and T47D, which predominantly express hCT1a and hCT1b receptor isoforms (hCTR1a, hCTR1b) at a similar total number of hCT-binding sites. In MCF-7 cells, half-maximal inhibition (IC50) of [125I]amylin binding by human amylin was observed at 3.6 +/- 0.8 nM (n = 6). hCT and hCGRP-I displaced [125I]amylin binding with 22 and 66 times higher IC50. [125I]hCT binding was inhibited by hCT with an IC50 of 8.1 +/- 1.9 nM (n = 5), and human amylin and hCGRP-I were over 100 times less potent. In T47D cells, on the other hand, specific binding of [125I]amylin was not observed, but hCT inhibited [125I]hCT binding with an IC50 of 3.2 +/- 0.4 nM (n = 3), and human amylin and hCGRP-I had over 200 times higher IC50. In MCF-7 cells, half-maximal stimulation (EC50) of cyclic AMP accumulation by human amylin, hCT and hCGRP-I occurred at 1.4 +/- 0.2, 1.7 +/- 0.4 and 6.3 +/- 1.3 nM respectively. In T47D cells, the EC50 of hCT was 0.32 +/- 0.02 nM (n = 3), and 30- and 1900-fold higher with human amylin and hCGRP-I. In conclusion, the expression of hCTR1a and hCTR1b and [125I]hCT binding were indistinguishable in MCF-7 and T47D cells. Yet, [125I]amylin binding was only recognized in MCF-7 cells, consistent with a distinct amylin receptor.

hCG-Leydig cell functional binding kinetics: threshold and nonlinearity in response

1980 ◽  
Vol 238 (3) ◽  
pp. E293-E302
Author(s):  
W. R. Moyle ◽  
M. Netburn ◽  
A. E. Cosgrove ◽  
J. Krieger ◽  
O. P. Bahl
Keyword(s):  
Activation Energy ◽  
Cyclic Amp ◽  
Leydig Cell ◽  
Binding Sites ◽  
Receptor Occupancy ◽  
Binding Kinetics ◽  
Receptor Complex ◽  
Cyclic Amp Accumulation ◽  
Kinetics Of ◽  
Testosterone Synthesis

Functional kinetic methods, developed to measure the interaction of human chorionic gonadotropin (hCG) with rat Leydig-cell receptors, appear to be useful tools for correlating response with receptor occupancy. In the functional procedures, hCG was allowed to bind to the cells (period I), the free hormone was removed by washing and/or antiserum treatment (period II), and the response of the cells was measured at 37 degrees C (period III). Once initiated, the response to hCG was stable throughout period III. Assuming a one-to-one relationship between occupancy and response during period III, we estimated the rate of association to be 10(8) M-1/min at 37 degrees C with an activation energy of 14-17 kcal/mol. Removal of sialic acid from hCG increased this rate; removal of other carbohydrate residues decreased it. Similar values for the kinetics of binding were observed when either steroidogenesis or cyclic AMP accumulation was measured, suggesting that the same receptor may mediate both processes. Use of either functional or direct (i.e., 125I-labeled hCG) methods to estimate response as a function of occupancy gave equal results, suggesting that most binding sites were coupled to a response. Response was nonlinearly coupled to occupany. Threshold amounts of hormone-receptor complex (0.1% total receptors testosterone synthesis; 2.7% total receptors cyclic AMP accumulation) were required to induce any response. Increased stimulation required progressively larger increments of receptor occupancy. The threshold was inversely proportional to the efficacy of the hCG derivative used and was reduced by the presence of isobutylmethylxanthine.

scholarly journals Effects of adrenalectomy on binding to and actions of adrenergic receptors

1986 ◽  
Vol 237 (2) ◽  
pp. 527-531 ◽  
Author(s):  
M F el-Refai ◽  
T M Chan
Keyword(s):  
Cyclic Amp ◽  
Binding Sites ◽  
Adrenergic Receptors ◽  
Adrenergic Receptor ◽  
Glycogen Phosphorylase ◽  
Beta Adrenergic ◽  
Cyclic Amp Accumulation ◽  
Adrenergic Antagonists ◽  
Adrenergic Activation ◽  
Adrenalectomized Rats

Adrenalectomy results in significant changes in the mechanism of adrenergic activation of hepatic glycogenolysis. In adrenalectomized rats a greater role for the beta-adrenergic receptor is observed, whereas the alpha 1-adrenergic-mediated phosphorylase activation declines. Our present findings document that adrenalectomy causes a significant decrease in the high-affinity population of the alpha 1-adrenergic receptor labelled with [3H]adrenaline. Our data indicate a large increase in the number of beta-adrenergic binding sites after adrenalectomy. This increase was not consistent with the observed modest increase in the beta-adrenergic-mediated activation of cyclic AMP accumulation and glycogen phosphorylase. When alpha-adrenergic antagonists are present along with the catecholamine, a 100% increase in the adrenaline-mediated accumulation of cyclic AMP in hepatocytes from adrenalectomized rats was observed. Adrenalectomy was also shown to cause a significant increase in the hepatic alpha 2-adrenergic binding sites. These data are consistent with an inhibitory role on the beta-adrenergic-mediated activation of glycogenolysis by the hepatic alpha 2-adrenergic receptor in adrenalectomy.

Induction And Potentiation Of Platelet Aggregation By Clonidine And 7ρ-Aminoclonidine, Partial Agonists Of The α2-Receptor Which Regulates Platelet Adenylate Cyclase

1981 ◽  
Author(s):  
David C Stump ◽  
Donald E Macfarlane
Keyword(s):  
Platelet Aggregation ◽  
Cyclic Amp ◽  
Adenylate Cyclase ◽  
Specific Binding ◽  
Phase 1 ◽  
Intrinsic Activity ◽  
Second Phase ◽  
Adrenergic Agents ◽  
Cyclic Amp Accumulation ◽  
Induced Aggregation

Epinephrine induces platelet aggregation, potentiates aggregation by other agents, and blocks the stimulation of the adenylate cyclase by prostaglandins. Synthetic α-adrenergic agents have not been shown to induce aggregation. The effects of clonidine, an α2-agonist, and ρ-aminoclonidine on platelets were examined. Clonidine potentiated aggregation induced by 0.5μM ADP by 1.4-fold (1/2 max 0.5μM). It did not induce significant aggregation itself, and it inhibited aggregation induced by 5μM epinephrine (1/2 max lμM). It inhibited cyclic AMP accumulation induced by PGE1 by a maximum of 25% (1/2 max O.lμM) and it blocked inhibition by epinephrine. No significant specific binding of [3H] clonidine was observed to intact platelets. ρ-Aminoclonidine induced aggregation with delayed second phase (1/2 max 0.2μM), and potentiated ADP aggregation by 2-fold (1/2 max 0.2μM). Aggregation induced by epinephrine was more rapid, and was partially inhibited by ρ-aminoclonidine. It inhibited cyclic AMP accumulation by 50% max (1/2 max O.lμM) and attenuated epinephrine’s effect to the same level. The direct effects of ρ-aminoclonidine were blocked by lμM yohimbine, a selective α2-antagonist. Both clonidine and ρ—aminoclonidine blocked the specific binding of [3H]yohimbine (1/2 max 0.5μM). These results suggest that the platelet bears an α2-receptor with affinity for epinephrine, ρ-aminoclonidine and clonidine as agonists but that these agents display differing intrinsic activity and/or receptor reserve.

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