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Biomedical subjects

T Bartfai

Publications and source records attributed to T Bartfai.

At least 217 records · Page 12Linked to original sources
PubMed1983

In vitro and in vivo inhibition of [3H]imipramine binding by cadmium.

Chronic exposure of rats to CdCl2 altered the specific binding of [3H]imipramine to membranes from platelets and hypothalamus. There was a decrease in Bmax of 10-40% and a decrease in KD values of 30-40% as compared to the control group. In vitro studies on the inhibition of [ 3H ]imipramine binding to membranes from human and rat platelets and hypothalamus by CdCl2 corroborate the in vivo results which imply that the imipramine binding protein contains Cd2+-sensitive groups.

Animals↗
PubMed1983

Vasoactive intestinal polypeptide and muscarinic receptors: supersensitivity induced by long-term atropine treatment.

Long-term treatment of rats with atropine induced large increases in the numbers of muscarinic receptors and receptors for vasoactive intestinal polypeptide in the salivary glands. Since receptors for vasoactive intestinal polypeptide coexist with muscarinic receptors on the same neurons in this preparation, the results suggest that a drug that alters the sensitivity of one receptor may also affect the sensitivity of the receptor for a costored transmitter and in this way contribute to the therapeutic or side effects of the drugs.

Animals↗
PubMed1983

Orthovanadate induces loss of muscarinic cholinergic binding sites.

In homogenates of corpus striatum from rats, incubated in the presence of adenosine triphosphate (2 mM) (45 min, 37 degrees C), a loss (approx. 50%) of muscarinic cholinergic binding sites could be detected using a 3H-3-Quinuclidinyl benzilate (3H-3-QNB) binding assay. We found that only vanadium-contaminated ATP induced loss of muscarinic binding sites. Orthovanadate (1 mM) alone in the absence of ATP induced loss (approx. 60%) of binding sites just as "vanadium-ATP" did.

Adenosine Triphosphate↗
PubMed1983

Postmortem changes in binding to the muscarinic receptor from human cerebral cortex.

The effects of storage at 4 degrees C on the antagonist and agonist binding properties of the muscarinic acetylcholine receptor from fresh surgical and frozen autopsy samples from human cerebral cortex were studied. The number of L-[3H]3-quinuclidinyl benzilate binding sites and their affinities were stable up to 51 h, both when stored as pieces of intact nonfrozen tissue and as a homogenate. The agonist binding properties as measured by the ability of the muscarinic agonist carbachol to compete with L-[3H]3-quinuclidinyl benzilate were also stable up to 51 h when the tissue was stored in the form of pieces. The affinity for carbachol decreased when the tissue was stored as a homogenate. The frozen autopsy samples showed no significant differences in binding properties in comparison with fresh neurosurgical tissue.

Aged↗
PubMed1983

Presynaptic antagonist-postsynaptic agonist at muscarinic cholinergic synapses. N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)acetamide.

A muscarinic cholinergic ligand, N-methyl-N-(1-methyl-4-pyrrolidino-2-butynyl)-acetamide (Compound BM-5), was shown to act simultaneously as a presynaptic antagonist and as a postsynaptic agonist at peripheral and central muscarinic synapses. In the presence of eserine it enhanced release of [3H]acetylcholine evoked by electrical stimulation in the guinea pig ileum longitudinal muscle myenteric plexus preparation. It also enhanced the release of [3H]acetylcholine evoked by potassium (25 mM) from rat hippocampal slices. It contracted the ileum and stimulated the synthesis of cyclic guanosine 3',5'-monophosphate in rat hippocampal slices and in human lymphocytes in a manner similar to the muscarinic agonist oxotremorine. This effect of BM-5 could be blocked by atropine.

Acetylcholine↗
PubMed1982

Pre- and postsynaptic muscarinic receptors in surgical samples from human cerebral cortex.

The present study was carried out using fresh surgical material from human cerebral cortex of patients who were not medicated with atropine or other drugs known to affect the cholinergic system. The concentration of [3H]L-quinuclidinyl benzilate binding sites was 0.45 /+- 0.05 pmol/mg protein and the Kd-value of the receptor-[3H]L-QNB-complex was 0.038 /+- 0.005 nM. Agonist binding was studied by varying the concentration of carbamylcholine (10(-8) to 10(-2) M) in the presence of a constant concentration (0.2nM) of [3H]L-quinuclidinyl benzilate. The data revealed the existence of two populations of binding sites for carbamylcholine with different affinities and capacities. Presynaptic muscarinic receptors were studied in slices of the cerebral cortex, which were loaded with [3H]choline. The muscarinic antagonist, atropine (10(-6) and 10(-7) M) acting at the presynaptic muscarinic receptors enhanced the release of [3H] acetylcholine. It was also shown that muscarinic stimulation leads to elevation of cyclic GMP levels in the human cerebral cortical slices.

Acetylcholine↗
PubMed1982

Two ligands may bind simultaneously to the muscarine receptor.

Competition between 3H-3-quinuclidinyl benzilate (2 and 18 nM) and varying concentrations of antagonists (4-N-methyl piperidinyl benzilate (4-NMPB), atropine, scopolamine and pirenzepine (0-1000 nM) and agonists (acetylcholine, carbamylcholine, oxotremorine and pilocarpine (0.10(-10) to 10(-2) M)) was studied. Inhibition of specific 3H-3-quinuclidinyl benzilate binding was evaluated by Dixon plots which for both competing agonists and antagonists showed deviations from linearity. The best nonlinear least square fit to the Dixon plots was offered by a hyperbola, parabola or a straight line, depending on the ligand used. The data support a model of equilibrium binding which assumes that 3H-3-quinuclidinyl benzilate and one competing ligand molecule may simultaneously bind to the receptor at high concentrations of the competing ligand.

Animals↗
PubMed1982

Acetylarsenocholine: a cholinergic agonist.

The pharmacological properties of acetylarsenocholine, an arsenic analogue of acetylcholine, were investigated. Acetylarsenocholine behaved as a cholinergic ligand both in the central and peripheral nervous system. It bound to nicotinic receptors in rat medulla-pons with a KD of 15 microM and to muscarinic receptors in rat cerebral cortex with a KD of 10 microM. It behaved also as an agonist at presynaptic muscarinic receptors in guinea pig ileum myenteric plexus preparation. Arsenocholine is an alternative substrate for choline acetyltransferase and acetylarsenocholine is an alternative substrate for acetylcholinesterase.

Animals↗
PubMed1982

The effects of atropine on [3H]acetylcholine secretion from guinea-pig myenteric plexus evoked electrically or by high potassium.

1. The myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum was incubated with [(3)H]choline (1.125-1.5 muM), and then superfused with Tyrode solution containing hemicholinium-3 (10 muM). Secretion of [(3)H]acetylcholine ([(3)H]ACh) was evoked either (a) by electrical field stimulation (0.5-15 Hz, 150 shocks per period, 0.5 msec), used to ;indirectly' depolarize the varicosities of nerve terminals, or (b) by high potassium (40 mM with 1 muM-tetrodotoxin, for 6 min, or 80 mM without tetrodotoxin, for 1 min), to ;directly' depolarize varicosities.2. With these stimulation parameters, which yielded about the same fractional secretion of [(3)H]ACh, and with eserine (10 muM) present in the medium, atropine (1 muM) enhanced the ;indirectly', electrically evoked secretion 3.65+/-0.34 (n = 6) fold, and that caused by 40 mM or 80 mM-potassium 1.82+/-0.06 (n = 6) or 1.55+/-0.09 (n = 10) fold, respectively. Atropine thus enhanced ;indirectly', electrically evoked secretion 4-fold more than that caused by ;direct' depolarization of varicosities with high potassium (P < 0.001).3. This difference is not likely to be caused by depression of the sensitivity of the presynaptic muscarinic receptors to ACh released by nerve stimulation, caused by the hypertonicity of the medium in the potassium stimulation experiments. The medium made hypertonic by addition of Tris-HEPES (80 mM) did lower the binding affinity of membrane preparations of (pre- and post-synaptic) muscarinic receptors, to carbamylcholine, and also the contractile responsiveness of the longitudinal muscle to this agent, in both cases to about one half. But it did not appear to alter the responsiveness of either pre- or post-synaptic muscarinic receptors to endogenous ACh, released by nerve stimulation.4. The results support a dual-mode model for the muscarinic negative feed-back control of ACh secretion from the nerve terminals of this preparation, mainly operating by restriction of the invasion of terminals, and only secondarily by depression of the efficiency of depolarization-secretion coupling in invaded varicosities.5. Since this model has earlier been proposed to apply for the control of secretion of [(3)H]noradrenaline from the micro-anatomically similar nerve terminals of noradrenergic nerves, the present findings suggest that the model may have a wider biological significance, and possibly apply to the control of the secretory activity of boutons-en-passant nerve terminals in general.

Acetylcholine↗
PubMed1981

Muscarinic supersensitivity induced by septal lesion or chronic atropine treatment.

Nine days after medial septal lesion a 20% increase in the number of muscarinic antagonist binding sites in rat hippocampus was observed without any change in the affinity for agonist or antagonist. Chronic atropine treatment (s.c. 5 mg/kg, twice a day for 14 days, 20 mg/kg once a day for 14 days or 100 mg/kg for 4 days and 20 mg/kg for 10 days, once daily) led to an increase in the number of muscarinic antagonist binding sites in rat hippocampus with 35, 80 and 80% respectively and also lowered the affinity for 3H-antagonists in a dose dependent manner. Agonist binding studies also indicated an increase in receptor number and a decrease in affinity. The latter change can possibly be explained by the presence of residual atropine 24 h after the last injection. If this is taken into account we may conclude that muscarinic supersensitivity evoked either by severing the input or by chronic pharmacologic blockade both produced "new receptors' with ligand binding properties similar to the original receptors.

Animals↗
PubMed1981

Binding of [3H]-pilocarpine to membranes from rat cerebral cortex.

Binding of [3H]-pilocarpine to synaptic membranes in rat cerebral cortex was investigated, pilocarpine binding was also studied by competition of unlabelled pilocarpine with the [3H]-labelled muscarinic antagonist, [3H]-N-methyl-4-piperidinyl benzilate. 1. [3H]-pilocarpine binding sites are of protein nature, and the highest specific activity of binding is found in the synaptosomal fraction of all subcellular fractions. 2. Competition studies show that only muscarinic drugs inhibit [3H]-pilocarpine binding in their pharmacologically active concentration range. 3. Binding of [3H]-pilocarpine is influenced by GMPP-(NH)P (0.1 mM) similarly to the binding of other muscarinic agonists. 4. Examination of pilocarpine binding with [3H]-pilocarpine and the competition experiments with unlabelled pilocarpine indicate the presence of three sites with different affinities: 5 nM, 0.2 microM and 30 microM respectively. 5. Experiments with [3H]-4-NMPB and [3H]-pilocarpine indicate that there are more [3H]-pilocarpine binding sites than [3H]-4-NMPB binding sites in rat cerebral cortex.

Animals↗
PubMed1981

Site(s) and ionic basis of alpha-autoinhibition and facilitation of "3H'noradrenaline secretion in guinea-pig vas deferens.

1. Mechanisms controlling the secretion of [(3)H]noradrenaline from the noradrenergic nerves of guinea-pig isolated vas deferens, prelabelled by incubation with [(3)H]noradrenaline, were studied using (a) different modes of (extramural or transmural) electrical nerve stimulation (a total of 300 shocks of varying strength, and a duration of 2 msec) at 1-30 Hz, or (b) depolarizing concentrations of K(+) (60-110 mm).2. The fractional rise in efflux of (3)H-labelled material (Deltat) was used to measure the secretion of [(3)H]noradrenaline.3. The dependence of [(3)H]noradrenaline secretion on the external Ca(2+) concentration (1-8 mm) was essentially hyperbolic. Double reciprocal plot analysis (1/Deltat vs. 1/Ca(2+)) of the data yields that blockade of alpha-autoinhibition (phentolamine 1 mum) does not increase the maximal secretory velocity, but does enhance the apparent affinity of the secretory mechanism for external Ca(2+). Exogenous noradrenaline has (qualitatively) opposite effects. The interaction between alpha-autoinhibition and external Ca(2+) thus shows a ;competitive' pattern, indicating that restriction of the utilization of external Ca(2+) is a major mechanism in alpha-autoinhibition of noradrenaline secretion, in this system.4. Phenoxybenzamine (10 mum) and phentolamine (1 mum) increased the secretion of [(3)H]noradrenaline evoked by depolarization with K(+) much less than that caused by electrical nerve stimulation (frequencies up to 10 Hz). Exogenous noradrenaline (1-5 mum) depressed the secretion evoked by both modes of stimulation. The results indicate that alpha-autoinhibition of [(3)H]noradrenaline secretion is mainly operative when the secretory stimulus requires conduction of nerve impulses between varicosities.5. The frequency dependence of [(3)H]noradrenaline secretion was hyperbolic, both in the presence and in the absence of alpha-autoinhibition; at each frequency the secretion (Deltat per shock) increased with the Ca(2+) concentration in the medium (0.6-8 mm). Double reciprocal plot analysis (1/Deltat vs. 1/frequency) of the data yields that the pattern of interaction between external Ca(2+) and facilitation depends on the presence or absence of alpha-autoinhibition (phentolamine 1 mum); in the former case it is ;non-competitive', in the latter ;competitive'. Similar analysis of the effect of facilitation by increasing the length of stimulus trains (from 5 to 300 pulses) at a constant frequency (5 Hz), on the Ca(2+) dependence of Deltat (1/Deltat vs. 1/Ca(2+)) in the absence of alpha-autoinhibition also yields that facilitation promotes utilization of external Ca(2+). These results apparently imply that a rise in external Ca(2+), in the presence of alpha-autoinhibition, augments the secretory response to electrical nerve stimulation mainly by promoting recruitment of active units (varicosities?), without markedly altering their ;affinity' for facilitation. In the absence of autoinhibition (when all units are already recruited?), the results seem to imply that facilitation promotes depolarization-secretion coupling in each, by more efficient utilization of external Ca(2+).6. The pattern of interaction between alpha-autoinhibition and facilitation depends on the Ca(2+)concentration in the medium. At or below the physiological level of Ca(2+) in extracellular fluid (1.2 mm) it is ;non-competitive', indicating that alpha-autoinhibition and facilitation act, at least in part, at separate targets under these conditions. At high (5.4 mm) external Ca(2+) the pattern becomes almost purely ;competitive', indicating that facilitation can, under suitable conditions, overcome all manifestations of alpha-autoinhibition.7. The secretion evoked by electrical nerve stimulation (Deltat per shock, at 1 or 10 Hz) increased with the strength of applied shocks, both when applied extra- or transmurally, in the presence or absence of alpha-autoinhibition. In the former case the rise in (Deltat per shock) vs. (current strength) was hyperbolic, in the latter it followed a biphasic pattern. Double reciprocal plot analysis (1/Deltat vs. 1/current) of the data yields a ;non-competitive' pattern of interaction between facilitation or alpha-autoinhibition, and exogenous current, when stimulation was extramural. When it was transmural the pattern is ;competitive'. The results seem to imply that hyperpolarization, or depolarization, of nerve terminals are major mechanisms whereby alpha-autoinhibition and facilitation, respectively, exert their effects on the secretory response to electrical nerve stimulation.8. Neither activation of Na(+), K(+)-ATPase, nor promotion of G(Cl) appear to be critically involved in alpha-autoinhibition. Experiments with known blockers of G(K) (tetraethylammonium, 4-aminopyridine and Rb(+)) did not give support to the notion that promotion of K(+) efflux is a mechanism whereby prejunctional alpha-adrenoceptors cause (hyperpolarization of nerve terminals and) autoinhibition of secretion. If alpha-autoinhibition does involve K(+) channels in the nerve terminal membrane, then these must be different from the (voltage-sensitive) K(+) channels blocked by the above mentioned inhibitors of K(+) efflux.9. The results are discussed in the context of a model that assumes that local control of noradrenaline secretion from noradrenergic nerves may be exerted both by control of invasion of terminals, and by control of depolarization-secretion coupling in each invaded varicosity. Under suitable conditions facilitation and alpha-autoinhibition may interact at both levels. It proposed that utilization of external Ca(2+) plays a pivotal role for both, and that restriction of invasion of nerve terminal varicosities is the main effect of alpha-autoinhibition, while promotion of depolarization-secretion coupling is the main effect of facilitation, at physiological concentrations of Ca(2+) in the medium. For the nerve the role of this dual control system is proposed to be to ensure ;rotational' activation of varicosities, and for the effector cell of noradrenergic junctions, to increase the signal/noise ratio.

Animals↗
PubMed1980

Kinetic studies on muscarinic antagonist-agonist competition.

The kinetics of the association and dissociation of the radiolabeled high affinity muscarinic antagonist N-[3H]methyl-4-piperidinyl benzilate was studied with the receptor from smooth muscle. Neither the agonists carbamylcholine and oxotremorine nor the antagonist atropine did influence the dissociation rate (k-2) of the receptor . antagonist complex. Binding of the antagonist (A) takes place in two consecutive steps: (formula: see text). Agonists did not seem to influence the dissociation constant (k-1/k+1) of the first binding step, while atropine caused a large increase in this constant. These results indicate that while antagonist-antagonist competition can be explained in terms of competition for the free receptor (R), antagonist-agonist competition cannot be fitted with such a simple model.

Animals↗