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Biomedical subjects

S Tucek

Publications and source records attributed to S Tucek.

At least 91 records · Page 5Linked to original sources
PubMed1984

Neuromuscular system of piglets with splayleg: the synthesis of acetylcholine and the myelinization and ultrastructure of peripheral nerve fibres.

No difference has been found between the activity of choline acetyltransferase in the sciatic nerve of one-day-old piglets with the syndrome of splayleg and in the sciatic nerve of apparently healthy piglets from the same breed. The maximum rates of total synthesis of acetylcholine in the homogenates of the sartorius, tibialis ant. and peroneus tertius muscles and the bromoacetylcholine -inhibitable portions of the acetylcholine-synthesizing capacity (corresponding to the activity of choline acetyltransferase in intramuscular branches and terminals of the motor nerves) were also the same in both groups of one-day-old animals. The number of myelinated fibres in the peroneal nerve of piglets with splayleg did not differ from that in the control group; it increased by 33% between the first and the seventh day of postnatal life in both groups. The only difference revealed by electron microscopy of the peroneal nerves between the animals with splayleg (or on the 7th day after birth, the animals that had recovered from the condition of splayleg) and the unaffected animals was a higher accumulation of glycogen granules in the axons of animals with splayleg. Biochemical and morphological data obtained in the present study thus support the view that an impairment of the function of peripheral nerves is unlikely to be responsible for the development of the splayleg syndrome.

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↗
PubMed1983

Acetylcoenzyme A and the synthesis of acetylcholine in neurones: review of recent progress.

A review of recent progress in the investigation of the following two problems is given: (a) the origin of actyl groups in the acetylcoenzyme A which is used for the synthesis of actylcholine in mammalian nerve cells; (b) the role of acetylcoenzyme A in the control of acetylcholine synthesis. The data reviewed are mainly those that have been published after the reviews by Quastel (1978), Tucek (1978) and Jope (1979).

ATP Citrate (pro-S)-Lyase↗
PubMed1982

Choline acetyltransferase in the heart of adult rats.

The distribution of choline acetyltransferase (ChAT, EC 2.3.1.6.) in the heart of adult rats has been reinvestigated in view of recent discoveries that acetylcholine (ACh) can be synthesized not only by ChAT, but also by carnitine acetyltransferase (CarAT, EC 2.3.1.7) and that it is possible to distinquish between the ACh-synthesizing activity of ChAT in intramuscular nerves and the CarAT-mediated extraneural synthesis of ACh by means of bromoacetylcholine (BrACh), a specific inhibitor of ChAT. BrACh (0.002 mmol/l) has been found to inhibit the synthesis of ACh in the atria by 66-85% and in the ventricles by only 19-29%. Bromoacetylcarnitine (BrACar, 0.02 mmol/l), and inhibitor of CarAT, inhibited the synthesis of ACh in the atria by 34% and in the ventricles by 74-80%. These findings indicate that ChAT is responsible for most of the synthesis of ACh observed in the homogenates of the atria; in the ventricles, it catalyses only a minor portion of the total ACh synthesis observed. In the investigation of the regional distribution of ChAT in the heart, the BrACh-sensitive part of ACh synthesis was taken as the measure of ChAT activity. The highest activity of ChAT (nmol ACh synthesized g-l.h-l) was found in the region of the sinoatrial node (1775); it decreased in the order: interatrial septum (781) greater than rest of the right atrium (712) greater than left atrium (416) greater than basal part of the right ventricle (366) greater than apical part of the right ventricle (250) greater than inter-ventricular septum (239) greater than basal and apical part of the left ventricle (208 and 205). The results indicate that earlier investigations of the distribution of ChAT in the heart provided a basically correct picture although the contribution of CarAT to the synthesis of ACh measured had not been excluded, and confirm that ChAT is present throughout the heart, including the apical parts of the ventricles, However, the sino-atrio-ventricular gradient of ChAT distribution is steeper when the contribution of CarAT to the synthesis of ACh is excluded.

Acetylcarnitine↗
PubMed1982

Acetylcoenzyme A and acetylcholine in slices of rat caudate nuclei incubated with (-)-hydroxycitrate, citrate, and EGTA.

The effects of (-)-hydroxycitrate (OHC) and citrate on the concentration of acetylcoenzyme A (acetyl-CoA) and acetylcholine (ACh) in the tissue and on the release of ACh into the medium were investigated in experiments on slices of rat caudate nuclei incubated in media with 6.2 or 31.2 mM K+, 0 or 2.5 mM Ca2+, and 0, 1, or 10 mM EGTA. OHC diminished the concentration of acetyl-CoA in the slices under all conditions used; in experiments with 2.5 mM OHC, the concentration of acetyl-CoA was lowered by 25-38%. Citrate, in contrast, had no effect on the level of acetyl-CoA in the tissue. Although both OHC and citrate lowered the concentration of ACh in the slices during incubations with 6.2 mM K+ and 1 mM EGTA, they had different effects on the content of ACh during incubations in the presence of Ca2+. The concentration of ACh in the slices was increased by citrate during incubations with 2.5 mM Ca2+ and 31.2 or 6.2 mM K+, but it was lowered or unchanged by OHC under the same conditions. The release of ACh into the medium was lowered or unchanged by OHC and lowered, unchanged, or increased by citrate. It is concluded that most effects of OHC on the metabolism of ACh can be explained by the inhibition of ATP-citrate lyase; with glucose as the main metabolic substrate, ATP-citrate lyase appears to provide about one-third of the acetyl-CoA used for the synthesis of ACh. Experiments with citrate indicate that an increased supply of citrate may increase the synthesis of ACh. The inhibitory effect of citrate on the synthesis of ACh, observed during incubations without Ca2+, is interpreted to be a consequence of the chelation of intracellular Ca2+; this interpretation is supported by the observation of a similar effect caused by 10 mM EGTA.

Acetyl Coenzyme A↗
PubMed1982

The synthesis of acetylcholine in skeletal muscles of the rat.

1. The synthesis of acetylcholine (ACh) has been measured in homogenates of the sciatic nerve, normal and denervated extensor digitorum longus (e.d.l.) muscles, and central (innervated) and peripheral (non-innervated) parts of the diaphragm of the rat. The synthesis proceeded under conditions accepted as optimal for the activity of choline acetyltransferase (ChAT). In view of the finding that cardiac carnitine acetyltransferase (CarAT) is able to acetylate choline (White & Wu, 1973), the possible contribution of CarAT to the synthesis of ACh in the muscles was investigated by using bromoacetylcholine (BrACh) as an inhibitor of ChAT and bromoacetylcarnitine (BrACar) as an inhibitor of CarAT.2. BrACh at a concentration of 2 mum inhibited the synthesis of ACh in nerve homogenates by 98%, in the homogenates of normal e.d.l. muscles by 53%, in denervated e.d.l. muscles by less than 5%; in the central part of the diaphragm BrACh inhibited ACh synthesis by 65%, and in the peripheral part by 13%. Comparative inefficiency of BrACh in inhibiting the synthesis of ACh in muscle homogenates was not due to its inactivation; the inhibitory effect of BrACh on the neural synthesis of ACh was preserved in the presence of muscle homogenates.3. BrACar at a concentration of 20 mum inhibited the synthesis of ACh in homogenates of the nerve by 18%, in those of normal e.d.l. muscles by 67%, in denervated e.d.l. muscles by 90%; in the central part of the diaphragm it inhibited the synthesis by 29%, and in the peripheral part by 76%.4. The inhibitory effects of BrACh and BrACar on the synthesis of ACh in muscle homogenates were roughly additive.5. Within 2 days of transection of the sciatic nerve, the BrACh-sensitive synthesis of ACh in the e.d.l. muscle diminished by 28%, whereas the BrACh-insensitive synthesis of ACh did not change. At 4 days after denervation, the rate of BrACh-sensitive synthesis decreased to 3% of control values.6. The results indicate that at least two enzymes are responsible for the synthesis of ACh in muscle homogenates is probably catalysed by CarAT. associated with intramuscular nerves, and probably corresponds to ChAT. The other enzyme is comparatively insensitive to BrACh, is sensitive to BrACar, and is probably localized in the muscle fibres. The BrACh-insensitive and BrACar-sensitive synthesis of ACh in muscle homogenates is probably catalysed by CarAT.7. Under the conditions used in the present experiments, CarAT was responsible for approximately one half of the synthesis of ACh in the homogenates of innervated e.d.l. muscles and for all ACh synthesized after denervation.8. The results provide an explanation for earlier findings of residual ACh synthesis in homogenates of denervated muscles, without resort to the idea that ChAT is localized in muscle fibres. It is proposed that CarAT catalyses some synthesis of ACh also in intact muscles, and that it is responsible for the synthesis of ACh observed during incubation of whole denervated muscles. It is not clear what is the physiological function of the synthesis of ACh catalysed by CarAT.9. Measurements of the BrACh-sensitive portion of the total ACh-synthesizing capacity of muscle homogenates provide a suitable procedure for obtaining information about the activity of neural ChAT in the muscles.

Acetylcarnitine↗
PubMed1982

Postnatal changes of the tonic influence of the vagus nerves on the heart rate, and of the activity of choline acetyltransferase in the heart atria of rats.

Postnatal changes in the resting heart rate and in its parasympathetic tonic inhibition have been measured in awake rats and compared with changes in the activity of choline acetyltransferase (ChAT) in the heart atria. The heart rate at rest increased from 372.min-1 on the 1st to 456 and 442.min-1 on the 15th and 24th day of life and then again decreased to 358 and 356.min-1 in 60-day-old and adult rats. Until the 15th day of postnatal life, the administration of atropine did not bring about an increase in the heart rate; the cardio-acceleratory effect of atropine (indicating the presence of tonic vagal inhibition of the heart) appeared only on the 18th day and increased steeply up to the 40th day of postnatal life. The activity of ChAT in the heart atria was measured as the difference between the synthesis of acetylcholine in atrial homogenates incubated in the absence and in the presence of bromoacetylcholine (BrACh), a specific inhibitor of ChAT; this procedure eliminated the contribution of carnitine acetyltransferase to the synthesis of acetylcholine. The activity of ChAT was found to increase steeply from the 1st to the 25th days of postnatal life; the steepest increase in the activity of the enzyme occurred between the 4th and the 15th days. Temporal correlation between the changes in the activity of ChAT, in the content of acetylcholine in the heart atria (Kuntscherová and Vlk 1979) and in the efficiency of transmural stimulation of sinoatrial region on the heart rate (Vlk 1979) indicate that the functional maturation of intracardiac cholinergic neurones, proceeding in rats during the first three weeks of their postnatal life, plays an important role in the onset and temporal development of the tonic parasympathetic inhibition of the heart rate.

Acetylcholine↗
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↗
PubMed1981

Comparison between grafts with intact nerves and standard free grafts of the rat extensor digitorum longus muscle.

Standard grafts and nerve-intact grafts of the extensor digitorum longus muscle were compared in the rat. In standard grafts the muscle was completely removed from its bed and replaced; nerve-intact grafts were treated in an identical manner except that the muscle nerve was not severed. Nerve-intact grafts underwent the same sequence of skeletal muscle fibre degeneration and regeneration as standard grafts. In nerve-intact grafts the intramuscular portions of the nerve fibres initially degenerated, but within a week new nerve fibres had regenerated back to the original zone of motor end-plates. By 60 days the weight of nerve-intact grafts approached those of control muscles. Contractile tension in nerve-intact grafts was greater than that of standard grafts. In standard and nerve-intact grafts choline acetyltransferase activity rapidly decreased to low values and then increased along curves roughly paralleling the muscle weights. In nerve-intact grafts, neuromuscular transmission was established early in the second week whereas a considerably later return was seen in standard grafts. Either the early onset or the topographical pattern of reinnervation are potentially major factors in determining the success of free muscle grafts.

Animals↗
PubMed1980

Relation between the content of acetyl-coenzyme A and acetylcholine in brain slices.

Slices of rat caudate nuclei were incubated in vitro in media containing, among other constituents, three different concentrations of glucose (0.5, 2 and 10 mM), 0.2 mM-choline, paraoxon as an inhibitor of cholinesterase, and 5 mM- or 30 mM-K+. After 30 and 60 min of incubation, the concentrations of acetyl-CoA, acetylcholine and choline in the tissue and of acetylcholine in the incubation medium were measured. The content of acetyl-CoA in the sliced varied in direct relation to the concentration of glucose in the incubation medium. The content of acetylcholine in the slices and, in experiments with high K+, also the amount of acetylcholine released into the incubation medium varied in direct relation to the concentration of glucose in the incubation medium and to the concentration of acetyl-CoA in the slices; the relation between the concentrations of acetyl-CoA and of acetylcholine in the slices was linear. It was concluded that the availability of acetyl-CoA had a decisive influence on both the rate of synthesis of acetylcholine and its steady-state concentration. The observations accord with the view that, at the ultimate level, the synthesis of acetylcholine is controlled by the Law of Mass Action.

Acetyl Coenzyme A↗