Telenzepine and its enantiomers, M1-selective antimuscarinics, in guinea pig lung function tests.
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Animals↗
Biomedical subjects
C Schudt
Publications and source records attributed to C Schudt.
Actions of the phosphodiesterase inhibitor zardaverine on guinea-pig ventricular muscle.
The positive inotropic action of the phosphodiesterase inhibitor zardaverine was investigated in guinea-pig heart muscle. In right papillary muscles, 1-30 microM zardaverine reversibly increased the force of contraction in a concentration-dependent manner. This effect was accompanied by a shortening of contraction and relaxation times. Resting membrane potential was unchanged, whereas action potential amplitude was significantly increased and duration was reduced. In papillary muscles partially depolarised with 22 mM K+, zardaverine (10 and 30 microM) restored slow action potentials, which were not influenced by cimetidine, propranolol or prazosin but were blocked by the calcium channel blocker (+)-nitrendipine or the muscarinic agonist carbachol. cAMP-specific phosphodiesterase III, isolated from guinea-pig ventricular muscle was inhibited by zardaverine as was cAMP-specific phosphodiesterase IV, isolated from dog trachea (IC50s: 0.5 and 0.8 microM, respectively). The results suggest that the observed positive inotropic and electrophysiological effects result from an inhibition of cellular phosphodiesterase.
1-Methyl-3-isobutylxanthine↗
Pharmacological characterization of muscarine receptors of PC12 (rat phaeochromocytoma) cells.
The muscarine receptors of PC12 (rat phaeochromocytoma) cells were studied in functional and binding experiments. The catecholamine stores of PC12 cells were labelled by incubation of the cells with tritiated noradrenaline. Muscarinic agonists elicited concentration-dependent release of tritium which consisted overwhelmingly of unchanged 3H-noradrenaline. The rank order of potency was: oxotremorine greater than acetylcholine greater than muscarine = methacholine greater than carbachol greater than bethanechol. The release evoked by carbachol (0.1 mmol/l) was inhibited with high potency by the M1-selective antagonist telenzepine (pKi = 8.82), with intermediate potency by pirenzepine (pKi = 7.00) and with low potency by the M2-selective antagonist AF-DX 116 (pKi = 5.74). The binding of 3H-N-methylscopolamine to PC12 membranes was inhibited by various non-selective and subtype-selective muscarinic antagonists with the following rank order of potency: telenzepine = atropine greater than 4-DAMP greater than dicyclomine greater than pirenzepine greater than HHSiD much greater than AF-DX 116. A similar rank order was obtained for the inhibition by these compounds of 3H-telenzepine binding to M1-receptors in membranes of the cerebral cortex of the guinea pig. The Hill coefficients for inhibition of 3H-N-methylscopolamine binding (to PC12 membranes) by pirenzepine, telenzepine and AF-DX 116 were below unity. Specific binding of both 3H-telenzepine and 3H-N-methylscopolamine to muscarine receptors of PC12 membranes was saturable and of high affinity; the maximal number of binding sites was higher for 3H-N-methylscopolamine than for 3H-telenzepine (calculated for the active (+)enantiomer). PC12 cells are presumably endowed with more than one subtype of muscarine receptors.(ABSTRACT TRUNCATED AT 250 WORDS)
Adrenal Gland Neoplasms↗
Hydrophobic calcium channel ligands: methodical problems and their solution.
Niguldipine is a 1,4-dihydropyridine derivative that combines L-type Ca2+ channel-blocking effects and alpha 1-adrenolytic activity within a single molecule, exemplifying a novel approach in the treatment of hypertension. As niguldipine is a very hydrophobic compound, it (1) readily adsorbs to surfaces of the plastic-ware often used in radioligand binding assays and (2) partitions into the hydrophobic membrane compartments. Both phenomena decrease the actual free drug concentration in radioligand-binding assays and lead to gross underestimation of the affinity of niguldipine (and other hydrophobic ligands) for the 1,4-dihydropyridine binding domain of the L-type Ca2+ channel or for alpha 1A adrenoceptors, respectively. Partitioning of the hydrophobic molecules into the membrane phase leads to a dependence of the Ki value on "total receptor" concentration despite mathematic corrections of the experimentally determined IC50 values. The Ki dependence was mimicked by adding denatured membranes (devoid of high-affinity receptor-binding activity) to native membrane preparations. Loss to pipet tips and tubes was avoided by a special dilution protocol. Partitioning into the hydrophobic membrane compartments needed more elaborate correction procedures.
Adsorption↗
Interaction of telenzepine with muscarinic receptors in mammalian sympathetic ganglia.
The interaction of the antimuscarinic drug telenzepine with muscarinic receptors was studied in rabbit and rat isolated superior cervical sympathetic ganglia. Radioligand binding demonstrated two muscarinic receptor sites in rabbit ganglia, with the characteristics of M1- and M2-receptors. Telenzepine bound to the M1 sites with a KI of 0.94 nmol/l and to the M2 sites with a KI of 17.8 nmol/l; the corresponding values for pirenzepine were 18.6 and 588 nmol/l; for AF-DX 116 the values were 891 and 33 nmol/l respectively. [3H]Telenzepine dissociated from the M1-receptors with a half time of 46 min at 37 degrees C. Electrophysiological experiments demonstrated that telenzepine reduced the amplitude of the extracellularly recorded slow excitatory postsynaptic potential and the slow inhibitory postsynaptic potential (ED50: 38 and 253 nmol/l respectively). In rat ganglia, application of muscarine or the M1-receptor agonist McN-A-343 increased the amplitude of submaximal population action potentials. This facilitation of synaptic transmission was potently blocked by telenzepine and pirenzepine but only weakly by AF-DX 116 (ED50: ca. 30, 150 and 20 mumol/l, respectively). It is concluded that telenzepine blocks the generation of the slow excitatory postsynaptic potential and the excitatory action of muscarine and McN-A-343 via an action on muscarinic M1-receptors.
Animals↗
The affinity, selectivity and biological activity of telenzepine enantiomers.
The binding of the enantiomers of telenzepine to muscarinic receptor subtypes present in guinea-pig cerebral cortex, myocardium and salivary glands has been examined. The (+) enantiomer is more potent in all assays and exhibits a greater selectivity than the (-) enantiomer for the different receptor subtypes. As a consequence, the enantiomeric potency ratio varies from ca. 400 (cortical 'M1' receptors) to ca. 50 (cardiac receptors). In functional assays in vitro in the rabbit vas deferens and rat atria, the affinity constants and enantiomeric potency ratios for the two isomers agree with those found for the appropriate muscarinic receptor subtype in binding assays. A high enantiomeric potency ratio, 180, is found in vivo for the ability of the telenzepine enantiomers to inhibit the production of lesions in the modified Shay rat preparation. The data are compatible with the blockade of M1 receptors by (+)-telenzepine being responsible for this action of telenzepine and would tend to exclude the possibility that the anti-ulcer action of telenzepine is mediated via a muscarinic or non-muscarinic action of the (-) enantiomer.
(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethy↗
(+)-Niguldipine binds with very high affinity to Ca2+ channels and to a subtype of alpha 1-adrenoceptors.
The enantiomers of the 1,4-dihydropyridine (DHP) niguldipine (3-methyl-5-[3-(4,4-diphenyl-1-piperidinyl)-propyl]- 1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl)-pyridine-3,5-dicarboxylate- hydrochloride) were investigated with respect to their interaction with 1,4-DHP receptors on L-type Ca2+ channels and alpha-adrenoceptors. The Ki values for niguldipine were dependent on the membrane protein concentrations in the radioligand binding assay. 'True' Ki values (at extrapolated 'zero' membrane protein) were determined with guinea-pig membranes for (+)-niguldipine and were found to be 85 pmol/l for the 1,4-DHP receptor of skeletal muscle, 140 pmol/l for that of brain and 45 pmol/l for that of heart. (-)-Niguldipine was approximately 40 times less potent. (+)-Niguldipine (Ki: 78 nmol/l) and (-)-niguldipine (Ki: 58 nmol/l) bound with approximately equal affinity to the alpha 1-adrenoceptors ('alpha 1B') in liver cell membranes. The (+)-niguldipine alpha 1-adrenoceptor inhibition data for rat brain cortex membranes were better fitted by a two-site model. The high-affinity component ('alpha 1A') had a Ki value of 52 pmol/l in competition experiments with [3H]prazosin. The low-affinity site (alpha 1B) had 200- to 600-fold less affinity. (-)-Niguldipine was greater than 40-fold less potent at alpha 1A- but was nearly equipotent to the (+)enantiomer at alpha 1B-sites. (+)-Niguldipine was the most selective compound for discriminating alpha 1A- from alpha 1B-adrenoceptors and is a novel prototype for 1,4-DHPs which bind with nearly equal affinity to skeletal muscle and brain or heart 1,4-DHP receptors.
Animals↗
The binding of a K+ competitive ligand, 2-methyl,8-(phenylmethoxy)imidazo(1,2-a)pyridine 3-acetonitrile, to the gastric (H+ + K+)-ATPase.
2-Methyl,8-(phenylmethoxy)imidazo(1,2-a)pyridine 3-acetonitrile (SCH 28080) is a freely reversible K+ site inhibitor of the gastric (H+ + K+)-ATPase. In the presence of 2 mMMgSO4, [14C]SCH 28080 bound saturably to gastric vesicle preparations containing the (H+ + K+)-ATPase and was displaced by lumenal K+. A binding stoichiometry of 2.2 +/- 0.1 mol of SCH 28080/mol of catalytic phosphorylation sites was observed. The affinity of SCH 28080 binding was increased approximately 10-fold (to 45 nM) in the presence of 2 mM ATP. High affinity binding also occurred with 2 microM ATP but not with up to 200 microM D-[beta, gamma-CH2]ATP, suggesting that high affinity binding was to a phosphorylated form of the enzyme. In the presence of ATP, the association rate constant was linearly related to the concentration of SCH 28080. However, the association and dissociation rates of SCH 28080 binding were slow, especially at low temperature (at 1.5 degrees C half-maximal binding of 50 nM SCH 28080 was calculated to occur after 232 s). Binding appeared to be predominantly entropy driven with a high activation energy (40 kJ/mol at 37 degrees C). In the absence of ATP, the association rate constant was not linearly related to the concentration of SCH 28080, suggesting that a conformational change in the enzyme was required before binding could occur.
Adenosine Triphosphatases↗
Is phosphodiesterase inhibition a relevant bronchospasmolytic principle?
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Asthma↗
The existence of stable enantiomers of telenzepine and their stereoselective interaction with muscarinic receptor subtypes.
[3H]Telenzepine has been shown to bind with high affinity (3 x 10(9) M-1) to a subpopulation of muscarinic binding sites in rat cerebral cortex, which have a high affinity for pirenzepine. The binding kinetics were very slow at 30 degrees. Only 50% of the [3H] telenzepine was found to be capable of binding to the receptors with high affinity. This suggested the presence of optical isomers of telenzepine. These were partially resolved on the picomole scale by using cortical muscarinic receptors to selectively bind the active isomer. It was then possible to measure the temperature and time dependence of the racemization of the inactive to the active enantiomer. The energy barrier for the inversion was 35 kcal/mol, and racemization was very slow even at 90 degrees. The affinity and selectivity of the unlabeled enantiomers for the different muscarinic receptor subtypes present on membranes from rat cerebral cortex, heart, and lacrimal gland was measured. The selectivity of active (+)-isomer was considerably greater than that of the (-)-isomer. As a consequence, the stereoselectivity of the enantiomers varied from 500 (M1 receptors in cerebral cortex) to 75 (cardiac receptors).
Animals↗
The binding of [3H]telenzepine to muscarinic acetylcholine receptors in calf forebrain.
Telenzepine binds to calf brain muscarinic receptors with a selectivity for M1 receptors that is comparable to that exhibited by pirenzepine. Telenzepine has a 10-fold higher affinity than pirenzepine at these receptors and is equipotent with atropine. Because of its potency, selectivity and hydrophilicity, [3H]telenzepine is an excellent radioligand for binding to and monitoring M1 receptor binding sites. The kinetics of [3H]telenzepine binding are extremely slow, even at 37 degrees C.
Animals↗
Does the prolonged occupancy of M1 receptors by telenzepine protect them against the action of vagally released acetylcholine?
The affinities of telenzepine, pirenzepine and atropine for muscarinic acetylcholine receptors have been determined by receptor binding studies using brain cortex and heart membranes of calf and rat. The ratios of affinities of telenzepine and pirenzepine for the cortical M1 receptors, cortical 'non-M1' receptors and cardiac M2 receptors are 50:5:1 and 80:5:1, respectively. The time course of association of telenzepine and pirenzepine with M1 receptors is similar, whereas the half-times for dissociation are 35 and 2.3 min at 37 degrees C, respectively. In further experiments this slow dissociation rate of telenzepine is shown to be rate-limiting for the occupation of M1 receptors by other ligands. The prolonged occupation of M1 receptors by telenzepine is discussed as a possible protective mechanism against acetylcholine released from vagal nerve fibers.
Acetylcholine↗
Specificity of the substituted benzimidazole B 823-08: a prodrug for gastric proton pump inhibition.
Substituted benzimidazoles are potent inhibitors of the parietal cell proton pump, the H+/K+-ATPase. One member of this group, the sulfide B 823-08 (2-[(4-methoxy-3-methyl-2-pyridylmethyl)-thio]-5-trifluoromethyl-(1H)- benzimidazole) inhibits gastric acid secretion in various in vivo models, but fails to affect acid secretion in the isolated, lumen perfused mouse stomach. In contrast, the corresponding sulfoxide (B 823-10) is active under both in vivo and in vitro conditions. Since the sulfide is metabolically transformed to sulfoxide in vivo, the sulfide behaves as a prodrug of the sulfoxide. No effects of biological significance are found on organ functions which critically depend on Na+/K+-ATPase activity. This is in line with observations that the sulfoxide needs activation in an acidic environment, which constitutes the basis of its specificity for inhibiting stimulated parietal cells.
2-Pyridinylmethylsulfinylbenzimidazoles↗
The sulphoxide moiety of substituted benzimidazoles is essential for inhibition of parietal cell K+/H+-ATPase.
The antisecretory action of the benzimidazole sulphoxide derivative B 823-10, 2[(4-methoxy-3-methyl-2-pyridylmethyl)-sulphinyl]- 5-trifluoromethyl(1H)-benzimidazole, was compared with the effect of the corresponding sulphide B 823-08 in several in vivo and in vitro and in vitro test systems. The sulphide B 823-08 and the sulphoxide B 823-10 were found to be equipotent in the Shay rat. The sulphide was found to inhibit H+ secretion in intact rabbit gastric glands and enriched guinea-pig parietal cells with lower potency than the corresponding sulphoxide. The relative potency in antisecretory activity (sulphide/sulphoxide) decreased in the following rank order: Shay rat: gastric glands: parietal cells. Purified K+/H+-ATPase was not blocked by the sulphide, whereas the sulphoxide inhibited the overall as well as the partial reactions of this enzyme. In all in vitro systems tested, inhibition of H+ secretion and enzyme activity by the sulphoxide, but not by the sulphide, was antagonized by SH-compounds such as dithiothreitol. It is concluded that in vivo sulphoxidation of the sulphide plays an important role in acid inhibition. In vitro an additional inhibitory mechanism of the sulphide has to be considered.
2-Pyridinylmethylsulfinylbenzimidazoles↗
Pharmacological evidence for selective inhibition of gastric acid secretion by telenzepine, a new antimuscarinic drug.
The new antisecretory drug, telenzepine (4,9-dihydro-3-methyl-4-[(4-methyl-1-piperazinyl)acetyl]-10H-thieno-[3,4 - b][1,5]benzodiazepin-10-one), was investigated for its inhibition of functionally intact muscarinic receptors involved in gastric acid secretion in rabbit fundic glands, perfused mouse stomach in vitro, perfused rat stomach in situ, gastric fistula in rats and dogs with a Heidenhain pouch. The effects on these receptors were contrasted with effects on receptors located on smooth muscle and heart, i.e. isolated rat urinary bladder, stomach and atrium. The results were compared to those values obtained with nonselective antimuscarinic drugs (N-methylscopolamine, atropine) and the selective M-1 antagonist pirenzepine. Telenzepine was found to be 4-10 times more potent than pirenzepine with respect to depressing both gastric acid secretion and smooth muscle or myocardial responses. Based on -log EC50 and pA2 values, both drugs exhibited a similar selectivity profile differing from the pattern of effects observed with atropine or a second reference compound, zolenzepine. As compared with atropine, telenzepine exhibited a 5 fold higher relative affinity to muscarinic receptors involved in gastric acid secretion. It was concluded that telenzepine is selective to discriminate between muscarinic receptors mediating gastric acid secretion and affecting muscle contractility and that this finding supports the concept of muscarinic receptor heterogeneity.
Aminopyrine↗
Effects of sodium 2-[5-(4-chlorophenyl)pentyl]-oxirane-2-carboxylate (POCA) on carbohydrate and fatty acid metabolism in liver and muscle.
In isolated rat hepatocytes, rates of gluconeogenesis, ketogenesis and oleate oxidation to CO2 were measured at various concentrations of lactate, pyruvate and oleate in the presence or absence of sodium 2-[5-(4-chlorophenyl)-pentyl]oxirane-2-carboxylate (POCA). With increasing lactate and pyruvate concentrations, but constant oleate concentration, oleate oxidation to CO2, concomitantly to gluconeogenesis, was accelerated, whereas ketogenesis was decreased. In the presence of POCA, rates of gluconeogenesis, ketogenesis and oleate oxidation to CO2 were diminished; the concentrations for half-maximal inhibition were in the micromolar range for all metabolic processes studied. When octanoate was present instead of oleate, the inhibitory effect of POCA on gluconeogenesis was reduced and that of ketogenesis was nearly abolished, suggesting that POCA specifically inhibits the oxidation of long-chain fatty acids. In addition, the oxidation of glucose and oleate was studied in isolated rat diaphragms. POCA inhibits the oxidation to CO2 of long-chain fatty acids also in muscle tissue; the concentration for half-maximal effect, however, was about one order of magnitude higher than in liver. Concomitantly, glucose oxidation was enhanced by POCA indicating a shift in the substrate preference of energy-yielding metabolism.
Animals↗
Cryofixation of monolayer cell cultures for freeze-fracturing without chemical pre-treatments.
A cryofixation method is presented which gives excellent ultrastructural preservation of monolayer cell cultures without any chemical pretreatments. Rat hepatocytes in primary culture were used in this study. The equipment needed is inexpensive and easy to manufacture. Cells are grown on a usual tissue culture support material (Thermanox plastic sheets). For cryofixation, samples are prepared essentially by a combined sandwich-cryogen-jet technique, 3 mm large discs are punched out and sandwiched with Cu- or Au-object holders of little mass; a 15 micrometer spacer is put in between. The viability of the cells is not impaired by the manipulations before freezing. The sandwich sample is quickly frozen by shooting a propane jet from a simple pressure chamber on to the metal object holder. The relevant parameters were optimized by parallel freeze-fracture analyses of 5% glycerol as a model system and by thermocouple measurements. Sandwich samples are then mounted in an appropriate double replication specimen table for further analysis by freeze-fracturing. It is possible to obtain a certain selectivity of the fracture plane with regard to apical, lateral or basal aspects of the cell layer. Alternatively, disc samples can be processed by chemical fixation methods (including freeze substitution to determine the freeze-fracture plane), since the support material Thermanox is insensitive to organic solvents and easy to cut. In each case the cells remain attached to their substratum throughout the whole procedure. Thus, the ultrastructural data can be directly correlated with parallel functional analyses obtained from the same cell cultures.
Animals↗
Influence of insulin, glucocorticoids and glucose on glycogen synthase activity in hepatocyte cultures.
A preparation method of monolayer cultures from rat hepatocytes with up to 95% plating efficiency is described. Cell number and DNA content per dish remained stable during 3 days in culture in hormone-free media containing 10 mM glucose. The cellular content of protein was decreased to 50% in the same time period. Glycogen content and specific activity of glycogen synthase present in the original hepatocyte suspension declined rapidly during 2 days in the absence of hormones. Addition of 20 nM insulin or 0.1 microM triamcinolone did not prevent this loss of cellular contents, however, in the simultaneous presence of both hormones the original levels of protein, glycogen and glycogen synthase were maintained for 2 days. In 2-day-old hepatocytes an increase of glycogen synthase activity could be evoked by insulin in the presence of 20 or even 5 mM glucose provided these cells had been precultivated in the presence of triamcinolone. Both the I-form and the activity determined at 6.7 mM glucose 6-phosphate rose after exposition of hepatocytes to insulin and 20 mM glucose, whereas a 'total activity' being unchanged by hormone treatment of the cells was only obtained if 50 mM glucose 6-phosphate were present during determination of enzyme activity. Addition of 10 microgram/ml cycloheximide during incubation of the cells reduced the effect of 20 mM glucose and abolished that of insulin on glycogen synthase and on the corresponding glycogen deposition. It is discussed that insulin and glucose activate glycogen synthase in two successive steps by regulating synthesis and activity of an interconverting enzyme.
Animals↗