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F Lübbecke

Publications and source records attributed to F Lübbecke.

30 records · Page 2Linked to original sources
PubMed1983

Radiation inactivation of alpha 1-adrenoceptors.

Radiation inactivation of alpha 1-adrenoceptors in rat cerebral cortex membranes has been performed with 10 MeV electrons from a linear accelerator at temperatures less than or equal to -100 degrees C. Alpha 1-adrenoceptor inactivation was monitored with [ 3H ]-prazosin and [( 125I ]-2-(beta-4-hydroxylphenyl)ethylaminomethyl)tetralone [( 125I ]-HEAT). Saturation analysis of irradiated membranes with both ligands indicated that a decrease in alpha-adrenoceptor density occurred with increasing radiation dose. The dissociation constants of [ 3H ]-prazosin and [ 125I ]-HEAT were not markedly changed by the irradiation. Application of the target volume theory gave molecular weights of 91,500 +/- 1,700 (S.D.) (D37: 19,6 +/- 0.36 Mrad) with [ 125I ]-HEAT as ligand, and 77,000 +/- 18,000 (S.D.) (D37: 23.3 +/- 4.6 Mrad) with [ 3H ]-prazosin, respectively, when an empirical temperature correction factor of 2.8 was used. [ 3H ]-flunitrazepam-labelled benzodiazepine receptor target size was used as an internal control. The molecular weight of the alpha 1-adrenoceptors, corrected for this internal control, was 85,000 +/- 1.600 [( 125I ]-HEAT) and 71,500 +/- 17,000 [( 3H ]-prazosin).

Animals↗
PubMed1983

Identification of voltage operated calcium channels by binding studies: differentiation of subclasses of calcium antagonist drugs with 3H-nimodipine radioligand binding.

3H-Nimodipine (3H-NIM) is a high affinity radioligand suitable to study Ca2+ -channels in a variety of tissues. The binding is saturable, reversible, and stereospecific in purified bovine heart and partially purified guinea-pig brain membranes. In the latter a Bmax of 600fmol/mg protein, dissociation constants (KD) of 0.4-0.8nM and a Hill slope of 1.0 are found. At 37 degrees C the optimal pH in 50mM TRIS-HCl buffer is 7.1-7.4. The calcium channel is a metalloprotein, and the divalent cation which is essential for the binding of 3H-NIM can be removed by EDTA (EC50 20 microM); the nimodipine binding site of the channel may then be reconstituted by divalent cations with Mn2+ greater than Ca2+ greater than Mg2+ greater than Sr2+. Ca2+ -antagonist drugs can be divided into three main classes based on their interaction with the 3H-NIM binding site: Class I has one site law of mass action-displacement isotherms with 3H-NIM, Class II exhibits complex biphasic inhibition profiles and Class III drugs increase the affinity of 1,4 dihydropyridines for the Ca2+ -channel. Diltiazem is a Class III Ca2+ -antagonist. Our in vitro studies lead us to conclude that the Ca2+ -channel contains multiple regulatory sites at which drugs can act.

Animals↗
PubMed1982

[125I]-HEAT:fifty percent of the ligand can bind to the alpha1-adrenoceptors with extremely high affinity.

[125]-HEAT, 125iodo-2-[Beta-(4-hydroxyphenyl)-ethyl-aminomethyl]tetralone, is a novel alpha1-adrenoceptor ligand which labels alpha1-adrenoceptors in peripheral tissues as well as in the central nervous system. Using the technique of ligand saturation by receptors, we find that only 50% of the 125I-labeled HEAT molecules bind with high affinity to receptors from a variety of tissues. This was observed with partially purified rat brain membranes and highly purified rat liver plasma membranes in the absence or presence of sodium ion (as NaCl, 150 mM) which stimulated 125I-HEAT binding, by increasing the affinity. If the bindability of [125I]-HEAT is taken into account, KD values as low as 7-8 pM (at 30 degrees C) are found in equilibrium binding experiments and optimally stimulating concentrations of sodium ion. The limited high affinity binding of [125I]-HEAT could not be explained by radiochemical impurities. Instead, we suggest that only one enantiomer of the racemic ligand is preferentially bound to the receptors with a KD in the picomolar range. Since the enantiomers are in dynamic equilibrium in solution (via keto-enol tautomerism) [125-I]-HEAT is a unique radioligand which makes it unlikely that the respective isomers can be separated by successive depletion with receptors.

Animals↗
PubMed1982

Effect of intraaortic balloon counterpulsation (IABP) on myocardial infarct size and collateral flow in an experimental dog model.

To determine the influence of IABP on infarct size and collateral blood flow in each of 12 openchest anaesthetised mongrel dogs two small branches of the left coronary artery were occluded consecutively. The perfusion areas of both branches were comparable in size. IABP was started immediately before ligation of the first branch for a 90-min period followed by a reperfusion period of 90 min. Subsequently the second vessel was also occluded for 90 min as a control without IABP while myocardial oxygen consumption remained constant and was then reperfused. Infarct size was expressed as a percentage of the perfusion area. A difference in infarct size with and without IABP (18 +/- 17, 18 +/- 10% respectively) could not be observed. However a significant increase of collateral blood flow due to IABP in the subendocardial layer from 8.9 +/- 4.8 to 14.9 +/- 4.6 ml/100 g/min (p less than 0.05) was prevalent. In the subepicardial layer the augmentation from 23.7 +/- 19.9 to 26.9 +/- 15.2 was not significant. Thus, in spite of a small increase of collateral blood flow in the subendocardial layer of the ischemic myocardium the infarct size was not reduced by IABP in our dog model.

Animals↗
PubMed1982

Ionic modulation of alpha-adrenoceptors.

Effects of cations and nucleotides on the in vivo binding properties of alpha-adrenoceptors in rat cerebral cortex membranes are described. Na+ ion converts a large fraction alpha-adrenoceptors in the absence or presence of Mg2+ into a low affinity state. The effects of 10 mM Na+ can be observed in 250 mM Tris-HCL buffer. It is suggested that alpha 2-adrenoceptor agonists alter the affinity of Na+ for a receptor-associated membrane component. alpha 2-Adrenoceptors are linked to guanylnucleotide binding proteins, which may be involved in signal transfer. These sites are altered in their nucleotide binding properties by pretreatment of the membranes with a medium that allows for ADP ribosylation or/and phosphorylation. alpha 1-Adrenoceptors were probed with a new, high affinity ligand, 125J-HEAT. 125J-HEAT binds (30 degrees C) with Kd values between 6 and 8 pM to alpha 1-adrenoceptors if Na+ slows down the dissociation of 125J-HEAT in comparison with MG2+. Na+ as well as Mg2+ reverse the inhibitory action of phosphatidic acid on the alpha 1-adrenoceptors labeled by 125J-HEAT. Data on the target size, obtained by radiation inactivation, of the alpha 1-adrenoceptors are presented.

Adrenergic alpha-Antagonists↗
PubMed1982

[3H]-Nimodipine and [3H]-nitrendipine as tools to directly identify the sites of action of 1,4-dihydropyridine calcium antagonists in guinea-pig tissues. Tissue-specific effects of anions and ionic strength.

We have performed a comparative binding study with tissues from the guinea-pig with the tritiated calcium antagonists [3H]-nimodipine (isopropyl-[2-methoxy-ethyl]-1,4-dihydro-2,6-dimethyl-4- [3-nitrophenyl]-3,5-pyridinedicarboxylate, Bay e 9736) and [3H]-nitrendipine (1,4-dihydro-2,6-dimethyl-4-[3-nitrophenyl]-3,5-pyridine carboxylic acid, 3-ethyl-5-methyl ester, Bay 3 5009). These compounds are potent nifedipine analogues. Binding of both tritiated calcium antagonists to heart, kidney, lung and brain membranes was evaluated under four different buffer conditions, namely TrisCl and TrisNO3, present at low and high ionic strength (50 and 500 mmol/l). Effects of anions, independent of ionic strength, were observed in brain membranes. In the lung membranes no [3H]-nitrendipine binding in excess above 10 mumol/l unlabelled calcium antagonist was observed at low ionic strength in either TrisCl or TrisNO3. The pharmacological profile of [3H]-nimodipine binding in brain membranes was that expected of a potent 1,4-dihydropyridine calcium antagonist. The apparent dissociation constant (KD) of [3H]-nimodipine for binding sites in brain membranes, determined in TrisNO3 buffer (50 mmol/l, pH = 7.4), was 0.3-0.4 nmol/l at 37 degrees C. The maximum number of binding sites (Bmax) was 300-350 fmol/mg of protein and is in the same range as is commonly observed for neurotransmitters, hormones or channel toxins.

Animals↗
PubMed1981

Cation sensitivity of [125I]heat binding to alpha 1-adrenoceptors in rat cerebral cortex membranes.

The alpha 1-adrenoceptor antagonist 2-[beta-(4-hydroxyphenyl)-ethylaminomethyl] tetralone (HEAT) was radiolabeled with 125I and purified to the maximal specific radioactivity of 2200 Ci/mmol. [125 I]HEAT selectively labels alpha 1-adrenoceptors (KD approximately 0.1 nM at 30 degrees C) in rat cerebral cortex membranes. Divalent cations stimulated [125 I]HEAT binding to the alpha 1-adrenoceptors. The rank order of potencies was Ni2+ greater than Mn2+ greater than Mg2+ greater than Ca2+ approximately Sr2+. The effect of Mg2+ was mainly on the Bmax of the alpha I-adrenoceptors. Monovalent cations also stimulated [125I]HEAT binding. Maximal stimulation (up to 3-fold) was seen with Na+ (optimal concentration at approximately 150 mM). Li+ and NH4+ were less effective whereas K+ was ineffective. The stimulation of [125I]HEAT binding to alpha I-adrenoceptors by Na+ was temperature-dependent.

Adrenergic alpha-Antagonists↗
PubMed1981

[3H]-Nitrendipine, a potent calcium antagonist, binds with high affinity to cardiac membranes.

The tritiated calcium antagonist 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-3,5-pyridine carboxylic acid, 3-ethyl-5-methyl ester (nitrendipine, Bay e 5009), a potent analogue of nifedipine, binds in a reversible and saturable manner to partially purified guinea-pig heart membranes. The analyses of the equilibrium binding data with Scatchard plots is in accord with either negative cooperativity of binding or with the assumption of two classes of binding sites, where one site has an equilibrium dissociation constant (Kd value) of 0.1 nmol/l and a density of 300 fmol/mg of protein. The binding sites are stereoselective and discriminate between (+)-nitrendipine and (-)-nitrendipine. We conclude that a high-affinity binding site at which 1,4-dihydropyridines bind, has now been identified with radioligand binding techniques. This site may well represent the locus where the potent 1,4-dihydropyridines exert their pharmacological action.

Animals↗
PubMedDate not supplied

Cardiac glycoside receptors in clinical and experimental states of chronic renal failure.

To investigate the mechanisms leading to decreased cardiac glycoside sensitivity in uremia, digitalis receptors were characterized by [3H]-ouabain binding to mononuclear leucocytes of chronically hemodialyzed patients and to cerebral cortex membranes of partially nephrectomized rats. There were no statistically significant differences in receptor density and affinity between uremic patients and healthy control persons and between partially nephrectomized and sham operated rats. [3H]-Ouabain bound with high affinity to intact mononuclear leucocytes and to cerebral cortex membranes. However, the affinity to the cerebral cortex membrane preparation was markedly higher.

Animals↗