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V Dolezal

Publications and source records attributed to V Dolezal.

At least 55 records · Page 3Linked to original sources
PubMed1988

Acetylcholine and choline in rat adrenals and brain cortex prisms incubated at elevated concentrations of choline in the medium.

Experiments were performed with rat adrenals and brain cortex prisms incubated in vitro in order to clarify whether it is possible to increase their acetylcholine (ACh) content by adding a high concentration of choline to the medium and whether the additional ACh formed can be released by subsequent depolarization. After 60 min incubation with 0.5 mmol/l choline, the concentration of ACh in the adrenals was increased by 116% (compared to the incubation without added choline), while in cortical prisms the observed increase (by 37%) was statistically non-significant. The content of ACh in both tissues was raised by paraoxon during incubations without added choline, but paraoxon did not augment the increased concentration of ACh in tissues incubated with added 0.5 mmol/l choline. The ACh that accumulated in the adrenals during 60 min preincubations with added choline could be released during subsequent depolarizing incubations; the release was Ca2+ independent. In contrast to brain cortex prisms and to the adrenals preincubated without choline, no resynthesis of ACh occurred during the period of depolarization in the adrenals preincubated with 0.5 mmol/l choline. Large amounts of choline accumulated in both tissues during incubations with 0.5 mmol/l choline and the accumulated choline could be released by depolarization; the release of choline from the adrenals was Ca2+ independent. Free choline was produced in the adrenals (presumably from choline esters) during the periods of depolarization. The reason for differences between the effects of increased concentrations of choline on ACh in the adrenals and in brain cortex is not known.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗
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↗
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↗
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↗
PubMed1983

Decrease of the spontaneous non-quantal release of acetylcholine from the phrenic nerve in botulinum-poisoned rat diaphragm.

Botulinum type A toxin (BoTx) has been found to diminish by 40% the spontaneous release of acetylcholine (ACh) from normal (acutely denervated) rat diaphragms incubated in the presence of 5 mM K+, while the release of ACh from chronically (4 days) denervated diaphragms was not affected during 2 h incubations. The toxin has been found to rapidly remove (within 10 min) the local depolarization of about 8 mV which developed in the end-plate zones of the diaphragms after the inhibition of cholinesterases; after the administration of BoTx, tubocurarine lost its ability to increase the resting membrane potential (H-response, Katz and Miledi 1977) in the end-plate area of anticholinesterase-treated muscles. It is concluded that BoTx inhibits the non-quantal release of ACh from the motor nerve fibres and that it probably acts directly on the nerve terminal surface membrane (without internalization). The H-response in the rat diaphragm reflects the non-quantal release of ACh from the nerve terminals and not from the muscle fibres.

Acetylcholine↗
PubMed1983

The synthesis and release of acetylcholine in normal and denervated rat diaphragms during incubation in vitro.

1. Normal and denervated rat diaphragms and neural (central) and aneural (peripheral) parts of normal diaphragms were incubated under several different conditions likely to affect the metabolism of acetylcholine (ACh), with the aim of discovering specific features of the control of neural and aneural ACh in the muscle. The concentrations of ACh in the tissue and the medium were measured at the end of the incubations using a radioenzymatic assay, and the amount of ACh synthesized during the incubations was calculated by subtracting the initial amount of ACh present in the tissue from that found in the tissue plus the medium at the end of the incubations.2. Confirming earlier results obtained with bioassays, it was found that, in a medium with 5 mM-K(+) and 2.5 mM-Ca(2+), denervated diaphragms released ACh into the medium at a rate equal to 47% of that observed in normal diaphragms; the amount of ACh released from aneural parts of normal diaphragms was 51% of that released from their neural parts. The release from normal diaphragms was increased (83%) in a Ca(2+)-dependent manner by raising the concentration of K(+) to 30 mM. In the denervated diaphragms, 30 mM-K(+) brought about a Ca(2+)-independent increase (67%) in the rate of ACh release. The elevation of K(+) was without effect on the release of ACh from aneural parts of normal diaphragms.3. The results indicate that a Ca(2+)-dependent mechanism of ACh release, known to function in the nerve terminals, is not likely to participate in the efflux of ACh from the muscle fibres. The K(+)-induced but Ca(2+)-independent enhancement of ACh release from the denervated diaphragms probably occurs by diffusion of ACh along the altered electrochemical gradient. It is suggested that the surface membranes of the muscle fibres become more permeable to ACh after denervation.4. During incubations with 30 mM-K(+) and 10 muM-hemicholinium-3 (HC-3), an inhibitor of the carrier-mediated transport of choline, the rates of ACh release and synthesis in normal diaphragms were diminished to the levels found in the denervated diaphragms, in which the concentration, release and synthesis of ACh were not affected by HC-3. The synthesis of aneural ACh thus appears to be independent of the carrier-mediated supply of choline across cell membranes.5. The release of ACh from normal diaphragms incubated with 5 mM-K(+) was increased in the presence of 100 muM-ouabain, whereas the release from denervated diaphragms was not affected. This finding suggests that the mechanism of ACh release that is activated by ouabain in the nerve cells involves, in addition to the inhibition of Na(+)-K(+)-ATPase, some other steps which are not operative in the muscle fibres.6. The results corroborate earlier evidence indicating that aneural ACh is produced, stored and released in the diaphragms. They fit the view that the aneural ACh is located in the cytoplasm of the muscle fibres and that it leaves the muscle fibres by molecular ;leakage' rather than by a specialized release mechanism. The efflux of ACh from the muscle fibres is likely to constitute about 50% of the total resting efflux (release) of ACh from normal diaphragms.

Acetylcholine↗
PubMed1982

[Oxygen toxicity].

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Adaptation, Physiological↗
PubMed1981

Utilization of citrate, acetylcarnitine, acetate, pyruvate and glucose for the synthesis of acetylcholine in rat brain slices.

Slices of rat caudate nuclei were incubated in saline media containing choline, paraoxon, unlabelled glucose, and [1,5-14C] citrate, [1-14C-acetyl]carnitine, [1-14C]acetate, [2-14C]pyruvate, or [U-14C]glucose. The synthesis of acetyl-labelled acetylcholine (ACh) was compared with the total synthesis of ACh. When related to the utilization of unlabelled glucose (responsible for the formation of unlabelled ACh), the utilization of labelled substrates for the synthesis of the acetyl moiety of ACh was found to decrease in the following order: [2-14C]pyruvate greater than [U-14C]glucose greater than [1-14C-acetyl]carnitine greater than [1,5-14C]citrate greater than [1-14C]acetate. The utilization of [1,5-14C]citrate and [1-14C]acetate for the synthesis of [14C]ACh was low, although it was apparent from the formation of 14CO2 and 14C-labelled lipid that the substrates entered the cells and were metabolized. The utilization of [1,5-14C]citrate for the synthesis of [14C]ACh was higher when the incubation was performed in a medium without calcium (with EGTA); that of glucose did not change, whereas the utilization of other substrates for the synthesis of ACh decreased. The results indicate that earlier (indirect) evidence led to an underestimation of acetylcarnitine as a potential source of acetyl groups for the synthesis of ACh in mammalian brian; they do not support (but do not disprove) the view that citrate is the main carrier of acetyl groups from the intramitochondrial acetyl-CoA to the extramitochondrial space in cerebral cholinergic neurons.

Acetates↗