PubMed Health⌕ Search

Biomedical subjects

S Tucek

Publications and source records attributed to S Tucek.

At least 73 records · Page 4Linked to original sources
PubMed1988

Calcium-independent release of acetylcholine from electric organ synaptosomes and its changes by depolarization and cholinergic drugs.

Chemiluminescent detection was applied to measure the continuous spontaneous Ca2+-independent liberation of acetylcholine (ACh) from Torpedo electric organ synaptosomes. Differentiation between the release of ACh and choline was achieved by inhibiting cholinesterases with phospholine, and a way to quantify the continuous release was devised. The method permitted measurements during short time intervals from minute amounts of tissue and without an accumulation of ACh in the medium. Synaptosomes continuously liberated small amounts of ACh during incubations in the presence of 3 mM K+ and in the absence of Ca2+. The spontaneous liberation of ACh was similar both quantitatively and qualitatively at pH values of 8.6 and 7.8. It was unaltered by MgCl2 (10.4 mM), 2-(4-phenylpiperidino)cyclohexanol (10 microM), ouabain (104 microM), atropine (10 microM), and valinomycin (102 nM). Carbamoylcholine brought about a decrease, which could be partially reversed by atropine. The Ca2+-independent output of ACh was increased considerably when the concentration of K+ ions was raised (eightfold at 103 and 35-fold at 203 mM K+). Carbamoylcholine (104 microM) blocked the increase in ACh release produced by high K+; this effect of carbamoylcholine was not reversed by atropine (10 microM). When Ca2+ was added to synaptosomes depolarized by a high concentration of K+, the amount of ACh released during the first 1-3 min after the addition of Ca2+ was at least 20 times higher than in the absence of Ca2+, but the release returned rapidly to predepolarization values. Similarly high values of ACh release could be achieved by adding Ca2+ plus the ionophore A23187 and even higher values by adding Ca2+ plus gramicidin.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
PubMed1988

A possible role for the acetylcholine transport system in non-quantal release of acetylcholine at the rodent myoneural junction.

The effects on the spontaneous, non-quantal release of acetylcholine (ACh) from motor nerve terminals of substances known to inhibit the ACh transport system present in cholinergic synaptic vesicles have been investigated. In mouse diaphragms, the hyperpolarization normally produced by d-tubocurarine (dTC) in muscle endplates that had been treated by an anticholinesterase was partly or completely abolished by 2-(4-phenylpiperidino) cyclohexanol (AH5183, 10(-7)-10(-6)M), quinacrine (10(-7)M) and tetraphenylborate (10(-6) M). Since the sensitivity of the endplate to ACh was not changed, the block of the dTC induced hyperpolarization indicated an inhibition of the spontaneous, non-quantal release of ACh. This was confirmed by direct measurement of the ACh released by rat diaphragm. The release of ACh from the innervated diaphragm was decreased by about 50% by AH5183 (10(-8)-10(-6) M) and by 42% by quinacrine (10(-7)-10(-6) M). The ACh released was presumably neural, since the release of ACh from 4-day denervated diaphragms was not diminished by either AH5183 or quinacrine. The results indicate that the spontaneous release of ACh from the motor nerve terminals is probably mediated by a carrier which may be the vesicular transport system responsible for moving ACh into the vesicle. The transport system is likely incorporated into the membrane of the nerve terminal during exocytosis.

Acetylcholine↗
PubMed1987

Pertussis toxin inhibits negative inotropic and negative chronotropic muscarinic cholinergic effects on the heart.

We injected rats with pertussis toxin, known to cause ADP ribosylation of the Gi regulatory protein of the adenylate cyclase complex and of another closely related GTP binding protein in the heart, and after 7 days we examined several effects of muscarinic activation on the heart. The negative chronotropic effect of carbamoylcholine on spontaneously beating perfused hearts was conspicuously diminished. While 10(-5) mol/l carbamoylcholine invariably produced heart arrest in control rats, the heart rate did not decrease by more than 20% in the toxin-treated rats even when the concentration of carbamoylcholine was raised to 10(-2) mol/l. The negative inotropic effect of carbamoylcholine examined on electrically paced ventricles perfused with isoproterenol was reduced, while the maximum positive inotropic effect of isoproterenol was substantially increased after toxin treatment. The inhibitory action of carbamoylcholine on the isoproterenol-stimulated accumulation of cyclic AMP in the heart auricles was attenuated. The weakening by pertussis toxin of the negative inotropic effect of carbamoylcholine is probably mainly due to the ADP ribosylation of the Gi regulatory protein and the subsequent loss of influence of muscarinic receptors on adenylate cyclase. The blockade of the negative chronotropic action of carbamoylcholine by pertussis toxin strongly indicates, together with other recently published evidence, that the Gi or another closely related GTP binding protein in the cardiac pacemaker cells is involved in the coupling of muscarinic receptors to the K+ channels.

Adenylate Cyclase Toxin↗
PubMed1987

Effect of lanthanum on the release of acetylcholine from the myenteric plexus and on its activation by ouabain and electrical stimulation.

The effect of lanthanum ions (La3+) on the release of acetylcholine (ACh) from longitudinal muscle strips of the guinea pig ileum with the myenteric plexus attached was investigated. After an exposure of the tissue to 2 mM LaCl3 for 18 min the rate of ACh release was increased approximately eightfold and the increased release lasted for more than 100 min. The augmented release of ACh was accompanied by enhanced synthesis. At the end of the experiments (102 min after LaCl3 had been removed), when the release of ACh was still more than six times higher than in controls, the content of ACh was the same in La3+-treated and untreated tissues. Electrical field stimulation failed to cause a further increase in the release of ACh from La3+-pretreated preparations whereas ouabain released considerable more ACh when compared to controls. It is concluded from this difference that electrical stimulation and ouabain release ACh from different pools.

Acetylcholine↗
PubMed1987

Failure of the calcium channel activator, Bay K 8644, to increase the release of acetylcholine from nerve terminals in brain and diaphragm.

The calcium channel activator Bay K 8644 did not increase the release of acetylcholine from rat brain cortex prisms incubated in the presence of 3 mmol l-1 or 25 mmol l-1 K+ nor from rat diaphragms incubated in the presence of 5 mmol l-1 or 25 mmol l-1 K+. It also did not influence the release of acetylcholine from cortex prisms incubated in the presence of 25 mmol l-1 K+ and of lowered concentrations of Ca2+ ions. It is concluded that the voltage-dependent Ca2+ channels in the nerve terminals, responsible for the depolarization-induced influx of Ca2+ ions into the nerve terminals and thus for the depolarization-evoked release of acetylcholine from the nerve terminals, are different from the voltage-dependent Ca2+ channels in the heart and smooth muscle cells.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Muscarinic acetylcholine receptors in the heart of rats before and after birth.

Atropine-displaceable binding of (3H)quinuclidinyl benzilate (QNB) to homogenates was used to identify the muscarinic binding sites in rat heart atria and ventricles and to investigate developmental changes in their concentration and binding properties between the 15th day of prenatal life and 3 months after birth. On the 15th day of prenatal life, muscarinic binding sites were already present in the heart. Their concentration increased steeply between the 15th and 19th days of prenatal development; in the atria, it remained high until the 1st day after birth and thereafter it diminished throughout the postnatal life, while in the ventricles the decrease started before the first postnatal day. The concentration of the binding sites was 1.8-3.0 times higher in the atria than in the ventricles at all time points investigated. Their affinity for QNB (the antagonist) was the same in the atria and ventricles and did not change during postnatal development (KD of 17.8 pmol/l at an infinitely low concentration of the binding sites). The binding of carbamoylcholine (the agonist) to muscarinic binding sites was analysed in experiments with the displacement of (3H)QNB binding, assuming the presence of high- and low-affinity binding sites for agonists. The proportion between the concentrations of the two classes of agonist binding sites is close to 1:1 both in the atria and the ventricles and does not change with age. No statistical significant differences were discovered between the affinities of the high- and low-affinity binding sites for carbamoylcholine between the atria and the ventricles and between new-born and adult rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

4-(1-Naphthylvinyl)pyridine decreases brain acetylcholine in vivo, but does not alter the level of acetyl-CoA.

The effects of intraperitoneally administered 4-(1-naphthylvinyl)pyridine (NVP; 200 mg/kg) on the concentrations of acetylcholine (ACh), choline (Ch), and acetyl-CoA (AcCoA) in rat striatum, cortex, hippocampus, and cerebellum were investigated. Twenty minutes after treatment, the content of ACh was significantly diminished, whereas that of Ch was increased. In response to stress (swimming for 20 min), these changes were enhanced. However, the AcCoA content did not change in any of the brain regions. It is thus very likely that the decrease of brain ACh concentration induced by NVP is due to the drug's effect on choline acetyltransferase (ChAT) and/or the reduction of the high-affinity Ch uptake, and not on the availability of AcCoA. Presumably, the pharmacologically diminished activity of ChAT may become the rate-limiting factor in the maintenance of ACh levels in cholinergic neurons.

Acetyl Coenzyme A↗
PubMed1986

Postnatal changes in the activities of acetylcholinesterase and butyrylcholinesterase in rat heart atria.

Postnatal development of the activities of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in rat heart atria has been investigated with the use of 1.5-bis (allyldimethylammoniumphenyl) pentane-3-dibromide (BW 284 C51) as a selective inhibitor of AChE. Total cholinesterase activity (mumol acetylthiocholine hydrolysed X g-1 per hour) increased from 218 on the 1st day after birth to 426 on the 30th day and diminished to 340 in adult rats. The activity of AChE (mumol acetylthiocholine hydrolysed X g-1 per hour) underwent more dramatic changes, increasing more than 4-fold during the first month of life, from 13 on the 1st to 58 on the 30th day of life and then decreasing to 42 in adult rats. The proportion of AChE on total cholinesterase activity increased from 6% on the 1st day to 12-15% in animals aged 24 days and more. Since AChE is known to be specifically involved in the termination of the action of acetylcholine in the sinoatrial node, the observed postnatal changes in its activity are likely to play a role in the postnatal development of cardiac parasympathetic control.

Acetylcholinesterase↗
PubMed1986

Stabilization of antagonist binding to cardiac muscarinic acetylcholine receptors by gallamine and other neuromuscular blocking drugs.

The effects of neuromuscular blocking drugs and muscarinic agonists and antagonists on the dissociation of [3H]quinuclidinylbenzilate ([3H]QNB) from muscarinic receptors was studied on rat atrial homogenates. In typical experiments the investigated drug was added to the homogenate equilibrated with [3H]QNB and the amount of undissociated [3H]QNB receptor complexes was measured 40 min later. The antagonists atropine and pirenzepine, agonists carbamoylcholine and methylfurmethide and neuromuscular blockers pancuronium, d-tubocurarine and decamethonium caused a concentration-dependent dissociation of [3H]QNB from the receptors, which may be explained by their competition with [3H]QNB for the same (primary) binding sites. In accordance with this, these drugs did not affect the dissociation of [3H]QNB elicited by an excess of atropine, which indicates that the kinetics of dissociation of the [3H]QNB receptor complex remained unchanged in their presence. Neuromuscular blockers alcuronium, gallamine and to a lesser degree tercuronium differed from the other drugs in that 1) their effect on [3H]QNB dissociation was biphasic, being higher at their low (10(-6) to 10(-5) M) than at their high concentrations (10(-4) to 10(-3) and that 2) at high concentrations they strongly inhibited the dissociation of [3H]QNB receptor complexes elicited by the excess of atropine. Their behavior may be rationalized by assuming that at low concentrations they bind to the primary binding site making rebinding of once dissociated [3H]QNB molecules improbable (competitive mechanism), whereas at high concentrations they also act on a secondary (allosteric) binding site stabilizing the [3H]QNB receptor complexes by slowing their off-kinetics.(ABSTRACT TRUNCATED AT 250 WORDS)

Allosteric Regulation↗
PubMed1985

Interaction of the neuromuscular blocking drugs alcuronium, decamethonium, gallamine, pancuronium, ritebronium, tercuronium and d-tubocurarine with muscarinic acetylcholine receptors in the heart and ileum.

Neuromuscular blocking drugs have a high affinity for muscarinic acetylcholine receptors in the heart atria and ileal smooth muscle. In experiments on homogenates, alcuronium, gallamine, pancuronium, tercuronium and ritebronium inhibited the binding of the muscarinic antagonist (3H)quinuclidinyl benzilate (QNB) to rat heart atria with IC50 values of 0.15-0.53 mumol X 1(-1) and to ileal longitudinal muscles with IC50 values of 0.12-0.45 mumol X 1(-1). d-Tubocurarine and decamethonium inhibited (3H)QNB binding to these tissues with IC50 values of 6.2-8.5 mumol X 1(-1). For each neuromuscular blocking drug, the IC50 values were virtually identical for (3H)QNB displacement in the homogenates of the atria and of the ileal muscle. Alcuronium and gallamine differed from the other blocking agents in that they produced less steep (3H)QNB displacement curves both in the atria and the ileal muscle; Hill coefficients for the binding of alcuronium and gallamine to atrial and ileal homogenates were lower than unity. On isolated atria, gallamine, pancuronium, ritebronium and tercuronium antagonized the inhibition of tension development caused by the muscarinic agonist, methylfurmethide, with Kd values which were of the same order of magnitude as the IC50 values for the displacement of (3H)QNB binding to homogenates; the Kd of alcuronium was 12.5 times higher. d-Tubocurarine and decamethonium did not antagonize the effects of methylfurmethide at concentrations up to 100 mumol X 1(-1). On isolated ileal longitudinal muscle, gallamine and pancuronium antagonized the effects of methylfurmethide with Kd values that were 53 times and 100 times higher than their respective Kd values in the atria.(ABSTRACT TRUNCATED AT 250 WORDS)

Alcuronium↗
PubMed1985

Is an acetylcholine transport system responsible for nonquantal release of acetylcholine at the rodent myoneural junction?

Experiments were performed to investigate the effects on the spontaneous, nonquantal release of acetylcholine (AcCho) from motor nerve terminals of substances known to inhibit the AcCho transport system present in cholinergic synaptic vesicles. In mouse diaphragms, the hyperpolarization normally produced by d-tubocurarine in the endplate area of muscle fibers that had been treated by an anticholinesterase was partly or completely blocked by 2-(4-phenylpiperidino)cyclohexanol (AH5183, 0.1-1 microM), quinacrine (0.1 microM), and tetraphenylborate (1 microM). Since the sensitivity of the subsynaptic area to AcCho was not changed, the block of the hyperpolarizing action of d-tubocurarine indicated in inhibition of the spontaneous, nonquantal release of AcCho. This was confirmed in experiments on rat diaphragm using direct radioenzymatic measurement of the AcCho released into the incubation medium. The release of AcCho from the innervated diaphragm was decreased by about 50% in the presence of AH5183 (0.01-1 microM) and by 42% in the presence of quinacrine (0.1-1 microM). The AcCho released was presumably neural, since the release of AcCho from 4-day denervated diaphragms was not diminished by either AH5183 or quinacrine. The results indicate that the spontaneous release of AcCho from the motor nerve terminals is highly sensitive to low concentrations of specific inhibitors and is probably mediated by a carrier. It is proposed that spontaneous release is due to the incorporation into the membrane of the nerve terminal during exocytosis of the vesicular transport system responsible for moving AcCho into the vesicle.

Acetylcholine↗
PubMed1985

Choline acetyltransferase activity and distribution in rat hearts after bilateral cervical vagotomy.

The activity of choline acetyltransferase (ChAt; E.C. 2.3.1.6) measured as the bromoacetylcholine-sensitive portion of the maximal rate of acetylcholine synthesis has been determined in homogenates of nine regions of the heart of control rats and rats sacrificed 72-74 h after bilateral cervical vagotomy. When related to the content of protein, the activity of ChAT was lowered by 30% in the atria and unchanged in the ventricles of vagotomized rats. The highest absolute decline caused by vagotomy was observed in the sinoatrial region; it was somewhat less in the rest of the right atrium and in the interatrial septum and considerably less in the left atrium. It is concluded that preganglionic parasympathetic fibres supply mainly the sinoatrial region and the right atrium, and that they do not branch to the ventricles. Preganglionic ChAT nts about 30% of total ChAT activity in the atria. The sinoatrio-ventricular gradient in the distribution of ChAT in the heart is due to uneven distribution of both the pre- and postganglionic ChAT pools (i.e., of both the pre- and postganglionic cholinergic nerve fibres and nerve cell bodies).

Animals↗
PubMed1984

Activation of muscarinic receptors stimulates the release of choline from brain slices.

The effect of several agents known to interact with muscarinic acetylcholine receptors on the release of choline from slices of rat corpus striatum into the incubation medium has been investigated. The amount of released choline was increased if choline, acetylcholine, or oxotremorine had been added to the incubation medium. Atropine blocked the effects of acetylcholine and oxotremorine; it was not tested with choline. It is proposed that the increased release of choline is due to an increased hydrolysis of phosphatidylcholine, brought about by the activation of muscarinic acetylcholine receptors.

Acetylcholine↗