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Biomedical subjects

T Bartfai

Publications and source records attributed to T Bartfai.

At least 235 records · Page 13Linked to original sources
PubMed1980

In vivo and in vitro studies of inhibitory effects of restorative dental materials on salivary esterases.

The influence of 18 dental materials on the activity of esterases isolated from human whole saliva has been studied. Eugenol on its own was a strong competitive inhibitor of the esterases II-2a (Ki = 3.3/10(-5) M) and II-2b (Ki = 4.7/10(-6) M). Except for Luralite all the materials that contained eugenol as one of the components (IRM, Nobetec and Opotow) were noncompetitive inhibitors. Additional in vitro inhibitors were: Adaptic, Aspa, Coe-pack and the amalgam ANA 68. Treatment with Nobetec packs in vivo resulted in a decrease activity of whole saliva.

Dental Materials↗
PubMed1980

Muscarinic autoreceptor regulates acetylcholine release in rat hippocampus: in vitro evidence.

Release of 3H-ACh from isolated nerve endings of rat hippocampus was evoked by incubation in Krebs-Ringer's buffer containing 25 or 35 mM potassium. The release was Ca2+-dependent and could be inhibited by Mg2+ (20 mM). The muscarinic antagonist, atropine (10(-10)-10(-6) M), enhanced 3H-ACh-release. The muscarinic agonist, carbachol (10(-5)-10(-3) M) inhibited 3H-ACh release via interaction with muscarinic receptors: this effect could be blocked by atropine (10(-6) M). The presence of the feed-back regulation of 3H-ACh release in a cell-free preparation provides further evidence that the presynaptic regulation is exerted by muscarinic autoreceptors localized on the cholinergic nerve ending itself. The feed back inhibition of the 3H-ACh release does not require the presence of intact neurons or neuronal loops as tetrodotoxin (2.5 x 10(-6) M) does not affect the above results.

Acetylcholine↗
PubMed1979

Isomerization of the muscarinic receptor . antagonist complex.

The mechanism of binding of two antagonists, 3-quinuclidinyl benzilate and N-methyl-4-piperidinyl benzilate, to the muscarinic receptor was studied. The pseudo-first order rate constant of association showed a hyperbolic dependence on the concentration of the antagonist(s) indicating that the interaction involves two equilibria. The first binding equilibrium is reached rapidly and is characterized by dissociation constants 2.7 +/- 0.4 nM and 6.7 +/- 2.5 nM in phosphate buffer (0.05 M, pH = 7.4) for 3-quinuclidinyl benzilate and N-methyl-4-piperidinyl benzilate, respectively. The first binding equilibrium is followed by a slower isomerization step of the receptor . antagonist complex. The equilibrium constants for the isomerization step of the complex for both ligands were about 0.15. The overall constant of binding obtained as the product of the above constants shows good agreement with the results of equilibrium binding studies.

Animals↗
PubMed1979

The influence of 8-Br 3', 5'-cyclic nucleotide analogs and of inhibitors of 3', 5'-cyclic nucleotide phosphodiesterase, on noradrenaline secretion and neuromuscular transmission in guinea-pig vas deferens.

The effects of 3', 5'-cyclic nucleotide phosphodiesterase (PDE) inhibitors and of 8-Br 3', 5'-cyclic nucleotide analogs on nerve-muscle transmission were studied in the guinea-pig vas deferens preincubated with 3H-noradrenaline. 8-Br cyclic AMP and the PDE inhibitors 3-isobutyl-1-methylxanthine (IBMX) and 3-propionyl-4-hydrazinopyrazolopyridine (SQ 20006) enhanced the secretion of 3H-NA evoked by transmural nerve stimulation. 8-Br cyclic GMP was without effect in this respect. The muscle contraction evoked by transmural nerve stimulation, high potassium or by application of exogenous noradrenaline was depressed by IBMX and SQ 2006. The contraction evoked by transmural nerve stimulation was enhanced by 8-Br cyclic AMP and depressed by 8-Br cyclic GMP. These findings suggest differential involvement of 3', 5'-adenosine- and guanosine-cyclic nucleotides in excitation-secretion-coupling in the noradrenergic sympathetic nerves, and in excitation-contraction-coupling in the smooth muscle, of guinea-pig vas deferens.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1978

Regulation of synthesis of guanosine 3':5'-cyclic monophosphate in neuroblastoma cells.

The increase in intracellular cyclic GMP concentrations in response to muscarinic-receptor activation in N1E-115 neuroblastoma cells is dependent on extracellular Ca2+ ion. The calcium ionophore A23187 can also evoke an increase in cyclic GMP in the presence of Ca2+ ion. Most (about 85%) of the guanylate cyclase activity of broken-cell preparations is found in the soluble fraction. The soluble enzyme can utilize MnGTP (Km = 55 micrometer), MgGTP (Km = 310 micrometer) and CaGTP (Km greater than 500 micrometer) as substrates. Free GTP is a strong competitive inhibitor (Ki approximately 20 micrometer). The enzyme possesses an allosteric binding site for free metal ions (Ca2+, Mg2+ and Mn2+). The membrane-bound guanylate cyclase is qualitatively similar to the soluble form, but has lower affinity for the metal-GTP substrates. Entry of Ca2+ into cells may increase cyclic GMP concentration by activating guanylate cyclase through an indirect mechanism.

Calcimycin↗
PubMed1978

Voltage-sensitive calcium channels regulate guanosine 3',5'-cyclic monophosphate levels in neuroblastoma cells.

Veratridine or high potassium concentration increased guanosine 3',5'-cyclic monophosphate (cGMP) levels in neuroblastoma cells of clone N1E-115 without affecting levels of adenosine 3',5'-cyclic monophosphate (cAMP). The increases in cGMP appear to be a direct result of the depolarizing action of these agents and not due to the action of substances released from the cells upon depolarization. The increase in cGMP produced by depolarization was dependent upon extracellular calcium and could be prevented by the calcium channel blockers D600 and cobalt. Carbachol, acting on muscarinic acetylcholine receptors, also caused a calcium-dependent increase in cGMP in these cells. The carbachol and potassium effects were additive from 5 to 100 mM potassium and from 1 to 3 mM calcium. The carbachol response was nearly as sensitive as the potassium response to inhibition by D600 but was much less sensitive to inhibition by cobalt. The results suggest that depolarization increases cGMP levels in these cells by opening voltage-sensitive calcium channels and that activation of muscarinic receptors opens separate, voltage-insensitive calcium channels.

Carbachol↗
PubMed1978

Immunological and binding studies on chloroform--methanol extracts from electroplax of Torpedo marmorata and from rat brain cortex. Comparison of the material solubilized by organic solvents with the receptor proteins solubilized by detergents.

We have investigated a chloroform--methanol extracted material from electric organ of Torpedo marmorata with respect to binding of [3H]-acetyl-alpha-neurotoxin and [3H]-acetylcholine. No binding was observed which is in contrast to observations with detergent extracted receptor. Further, no crossreactivity could be demonstrated between the chloroform--methanol extracted proteolipid and antibodies against the detergent extracted receptor. Labelling in the membrane with [3H]-acetyl-alpha-neurotoxin before extraction with chloroform--methanol gave a very low yield of extracted labelled compound. The protein yield is about 0.3% of the total in the homogenate and only 0.04% of the specifically bound neurotoxin. Using the alkylating affinity label [3H]-N-propylbenzilylcholine mustard (1) and also [3H]-atropine, which both bind, at low concentrations, specifically to the muscarinic acetylcholine receptor, binding was studied to the chloroform--methanol extracted proteolipid from rat brain cortex. No specific binding could, however, be demonstrated. Prelabelling in the membrane with 1 and subsequent extraction with chloroform--methanol gave a protein yield of about 1% and an extraction of 26% of the specifically bound label.

Acetylcholine↗
PubMed1977

Rate equations and simulation curves for enzymatic reactions which utilize lipids as substrates. I. Interaction of enzymes with the monomers and micelles of soluble, amphiphilic lipids.

Theoretical aspects of the kinetics of interaction of enzymes with lipid substrates are presented. Rate equations were written and used to simulate v versus S curves for interaction of enzymes with "monomers" (i.e. a molecular solution) or micelles (aggregated form) of the "soluble", amphiphilic lipids. The rate equations were written assuming separate kinetic parameters for the interaction of the enzyme with these two forms. Although the rate equations are based on the kinetic theory of Michaelis and Menten, most of the simulated v vs. S curves were not hyperbolic. A procedure is suggested for determining the kinetic parameters with the aid of a graphic method.

Colloids↗
PubMed1977

Rate equations and simulation curves for enzymatic reactions which utilize lipids as substrates. II. Effect of adsorption of the substrate or enzyme on the steady-state kinetics.

Theoretical aspects of the kinetics of interaction of enzymes with lipid substrates are presented. Rate equations were written and used to simulate v versus S curves for the following cases: (a) The substrate is adsorbed onto non-catalytic sites of the enzyme or to other proteins accompanying the enzyme. (b) The enzyme is adsorbed, via non-catalytic sites to aggregated forms of the substrate. (c) The substrate is adsorbed onto an externally added protein such as albumin. Although all rate equations are based on the Michaelis-Menten kinetic theory, most of the simulated v vs. S curves were not hyperbolic and some of the v vs. E curves not linear.

Adsorption↗
PubMed1976

Muscarinic acetylcholine receptor from rat brain. Partial purification and characterization.

A protein capable of binding atropine and (3H)propylbenzilylcholine mustard was solubilized and purified (200-fold) from rat brain. Pronase and trypsin, but not phospholipases, diminished the binding capacity of the solubilized receptor. The molecular weight of the salt-solubilized receptor as determined by gel filtration in the absence of detergents is 30,000. The purified protein showed specificity of binding toward muscarinic ligands. the high and low affinity dissociation constants of the receptor.atropine complex are 0.3 nM and 0.15 muM. Binding of atropine is pH-dependent with an optimum at 7.1. Ca2+ influences the binding of atropine and maximal binding occurs at 0.5 mM Ca2+. The subcellular distribution of the receptor was also examined.

Animals↗
PubMed1976

Isolation of a synaptic membrane fraction enriched in cholinergic receptors by controlled phospholipase A2 hydrolysis of synaptic membranes.

A procedure is described for the isolation of synaptic membrane fragments that retain such functionally important proteins as acetylcholine receptors, acetylcholinesterase, 3',5'-cyclic nucleotide phosphodiesterase, and (Na+ + K+)-ATPase. The method is based on the observation, made in brain slices, that junctional membranes are more resistant to phospholipase A2 attack than mitochondrial or plasma membranes. Hydrolysis by phospholipase A2 was controlled by addition of fatty acid-free bovine serum albumin. The membrane fraction obtained represents approximately a 15-fold enrichment of the postsynaptic marker proteins muscarinic and nicotinic acetylcholine receptor and 3',5'-cyclic nucleotide phosphodiesterase over an ordinary synaptic plasma membrane preparation, and is devoid of mitochondrial and microsomal contaminations. The membranes appear on the electron micrographs as rigid fragments (average length 2500-4000A), which do not form vesicles.

Animals↗