Effect of thiamine on neuromuscular transmission in smooth muscles

Effects of thiamine, thiamine monophosphate (TMP), and thiamine diphosphate (TDP) on excitatory cholinergic and inhibitory noncholinergic nonadrenergic neuromuscular transmissions were studied in the smooth muscles of the gastric fundus and in the circular layer of the distal colon of the guinea pig, respectively. It was found that, when applied in the physiological concentration range, thiamine, TMP, and TDP evoked depolarization and an increase in strain in the smooth muscle strips, as well as an increase in the amplitude of inhibitory synaptic potentials and postinhibitory depolarization. The amplitude of the excitatory synaptic potentials increases in the presence of thiamine and TMP, and decreases in the presence of TDP. The results obtained suggest that thiamine and TMP, which are normally present in the extracellular medium, may modulate synaptic transmission, as well as the electrical and contractile activity of the smooth muscles in the gastrointestinal tract.Neirofiziologiya/Neurophysiology, Vol. 26, No. 6, pp. 449–457, November–December, 1994.     

Pre- and post-synaptic actions of the cerebral ventral giant cell on buccal muscles ofPhiline

Summary The cerebral ventral giant cell ofPhiline exterts a selective presynaptic inhibitory modulatory action on the terminals of a buccal excitatory motoneuron in two buccal muscles. Other excitatory inputs to the muscles are not affected. The ventral giant cell also makes direct synaptic contacts on the fibres of the same muscles. In the retractor muscle M4, 5 the junction potentials are usually depolarising when measured in sea water, but in the fibres of M6 they may have either polarity. The mean membrane potential of the fibres of M4, 5 and M6 was –74.7±0.65 mV and –64±0.95 mV respectively. Depolarization of the muscles fibres by around 15 mV by immersion in 20 mM K saline abolished the junction potential in M4, 5 and converted the depolarizing potential in M6 to a hyperpolarizing response.It is concluded that the VGC junction potential results from an increase in membrane conductance to an ion with a reversal potential between –60 and –70 mV.     

Glutamatergic modulation of vertebrate neuromuscular transmission

The paper is devoted to the analysis of evidence pointing to presence of glutamatergic modulation of vertebrate neuromuscular transmission. The data on the glutamate's origin and release in the endplate region as well as on the presence of specific glutamate receptors are discussed. The effects of glutamate on different types of acetylcholine secretion in the synapses of amphibians and mammals are described. The question of possible physiological role of glutamatergic modulation of neuromuscular transmission is discussed.     

Biosynthesis of the thiazole moiety of thiamin pyrophosphate (vitamin B1)

While most of the proteins required for the biosynthesis of thiamin pyrophosphate have been known for more than a decade, the reconstitution of this biosynthesis in a defined biochemical system has been difficult due to the novelty of the chemistry involved. Here we demonstrate the first successful enzymatic synthesis of the thiazole moiety of thiamin from glycine, cysteine, and deoxy-D-xylulose-5-phosphate using overexpressed Bacillus subtilis ThiF, ThiS, ThiO, ThiG, and a NifS-like protein. This has facilitated the identification of the biochemical function of each of the proteins involved: ThiF catalyzes the adenylation of ThiS; NifS catalyzes the transfer of sulfur from cysteine to the acyl adenylate of ThiS; ThiO catalyzes the oxidation of glycine to the corresponding imine; and ThiG catalyzes the formation of the thiazole phosphate ring. The complex oxidative cyclization reaction involved in the biosynthesis of the thiamin thiazole has been greatly simplified by replacing ThiF, ThiS, ThiO, and NifS with defined biosynthetic intermediates in a reaction where ThiG is the only required enzyme.     

Structure-activity relationship of philanthotoxins--I. Pre- and postsynaptic inhibition of the locust neuromuscular transmission.

1. Like the natural toxin, synthetic delta-philanthotoxin, now called PTX-4.3.3 acts as a reversible postsynaptic open ion-channel blocker of the glutamatergic neuromuscular system of the locust. 2. It also inhibits the high-affinity re-uptake of glutamate in the nerve endings and glial cells. 3. To study the structure-activity relationship, three parts of the PTX-4.3.3 molecule were changed. 4. One of these PTX-analogues, trifluoromethyl-PTX-4.3.3, proved to be a more potent postsynaptic blocker. 5. Moreover, compared with PTX-4.3.3 a delayed recovery period is seen with trifluoromethyl-PTX-4.3.3. 6. A number of PTX-analogues were equipotent to PTX-4.3.3 regarding the inhibition of iontophoretically evoked, postsynaptic glutamate potentials. 7. However, complete inactivation was achieved by reducing the length of the polyamine chain, moreover dideaza-PTX-12 was nearly completely inactive and a reduced activity was seen with dephenol-PTX-4.3.3. 8. A decrease of the decay time constant of glutamate potentials, normally seen by open ion-channel blockers in Con A pretreated preparations, was unaffected during application of the latter two analogues. 9. Possibly these two toxins act as weak receptor antagonists. 10. The presynaptic inhibition of the glutamate re-uptake, seemed to be a very specific property of PTX-4.3.3. Only one of the tested analogues (dehydroxy-PTX-4.3.3) exhibited this capacity.     

Synaptic inhibition of smooth muscles of the human colon: Effects of vitamin B6 and its derivatives

Spontaneous activity, which is manifested as slow depolarization waves and action potentials, is observed in most (81%) smooth muscles (SMs) of the circular layer of the human colon. Independently of the type of pathology, inhibitory junction potentials (IJPs) in SMs of various parts of the human colon are evoked by intramural stimulation; ranges of parameters of these potentials were comparable with those observed in muscle intestinal fragments isolated at a distance of several tens of centimeters from the zone of injury. In muscle strips (MSs) of such fragments, pyridoxal-5′-phosphate (PPh) applied in different concentrations caused suppression of IJPs: in the concentration of 1·10⁻⁸ to 1·10⁻⁴ M it decreased the amplitude, and in the concentrations of 1·10⁻⁵ to 1·10⁻⁴ M and 1·10⁻⁴ M, respectively, it decreased rates of the half-amplitude rise and decay of these potentials. Pyridoxal (1·10⁻⁴ M) and 4-pyridoxolic acid (1·10⁻⁴ M) also caused a drop in the amplitude of IJPs; however, these agents influenced this parameter to a lesser extent, as compared with the effect of 1·10⁻⁴ M PPh. Pyridoxine (1·10⁻⁴ M) and pyridoxamine (1·10⁻⁴ M) evoked no significant changes in the parameters of IJPs in MSs of the human colon. Our data allow us to hypothesize that the suppressing effect of PPh on IJPs is determined by the presence of a purinergic component present in non-adrenergic inhibition of SMs of the human colon. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 269–279, July–August, 2006.     

Synthesis and antileishmanial evaluation of thiazole orange analogs

Cyanine compounds have previously shown excellent in vitro and promising in vivo antileishmanial efficacy, but the potential toxicity of these agents is a concern. A series of 22 analogs of thiazole orange ((Z)-1-methyl-4-((3-methylbenzo[d]thiazol-2(3H)-ylidene)methyl)quinolin-1-ium salt), a commercial cyanine dye with antileishmanial activity, were synthesized in an effort to increase the selectivity of such compounds while maintaining efficacy. Cyanines possessing substitutions on the quinolinium ring system displayed potency against Leishmania donovani axenic amastigotes that differed little from the parent compound (IC₅₀ 12–42 nM), while ring disjunction analogs were both less potent and less toxic. Changes in DNA melting temperature were modest when synthetic oligonucleotides were incubated with selected analogs (ΔTm ≤ 5 °C), with ring disjunction analogs showing the least effect on this parameter. Despite the high antileishmanial potency of the target compounds, their toxicity and relatively flat SAR suggests that further information regarding the target(s) of these molecules is needed to aid their development as antileishmanials.     

Nutritional modulation of gene expression and homocysteine utilization by vitamin B12

Vitamins B12, B6, and folic acid converge at the homocysteine metabolic junction where they support the activities of two key enzymes involved in intracellular homocysteine management, methionine synthase (MS) and cystathionine beta-synthase. The molecular mechanism for the regulation of homocysteine metabolism by B12 supplementation has been investigated in this study. B12 supplementation does not alter mRNA or protein turnover rates but induces translational up-regulation of MS by shifting the mRNA from the ribonucleoprotein to the polysome pool. The B12-responsive element has been localized by deletion analysis using a reporter gene assay to a 70-bp region located at the 3' end of the 5'-untranslated region of the MS mRNA. The cellular consequence of the B12 response is a 2- and 3.5-fold increase in the flux of homocysteine through the MS-dependent transmethylation pathway in HepG2 and 293 cells, respectively. It is speculated that B12-induced up-regulation of MS may have evolved as an adaptive strategy for rapidly sequestering an essential and rare nutrient whose availability may have been limited in the evolutionary history of mammals, a problem that is exacerbated by the absence of this vitamin from the plant kingdom.     

Seasonal variations in neuromuscular transmission in experiments on sectioned or curarized frog muscles

Evoked currents and endplate potentials in frog cutaneopectoral muscle subjected to section or curarization to prevent contraction were investigated in summer and winter conditions using different indirect stimulation rates (of 1 and 100 Hz), with animals maintained at different temperatures prior to trials (of between 5 and 20–25°C). Seasonal changes in amplitude, facilitation, and depression of postsynaptic response discovered in experiments involving curarized and uncurarized dissected muscles differed both quantitatively and qualitatively. These differences may be explained by assuming that sensitivity of the neuromuscular synapse to curare (presumably presynaptic) is liable to seasonal variation.A. A. Ukhtomskii Institute of Physiology, State University, Leningrad. Translated from Neirofiziologiya, Vol. 22, No. 6, pp. 745–751, November–December, 1990.     

Effect of B1 hypovitaminosis on the efficacy of neuromuscular transmission in the murine diaphragm

In mice kept on a diet with no vitamin B₁, the total content of thiamine in the brain decreased, and muscle contractions evoked by stimulation of the nerve in phrenico-diaphragmatic preparations obtained from such animals became weaker. The measurements were performed in Krebs solution with a decreased content of Ca²⁺ and increased concentration of Mg²⁺; values of the developed force were normalized with respect to those in normal Krebs solution. Thus, B₁ hypovitaminosis results in a decrease in the efficacy of neuromuscular synaptic transmission. Some neurological symptoms typical of a deficiency of vitamin B₁ in the organism can be related to this effect. Neirofiziologiya/Neurophysiology, Vol. 39, Nos. 4/5, pp. 416–418, July–October, 2007.     

Properties of sympathetic neuromuscular transmission and smooth muscle cell membranes in vascular beds.

In vascular smooth muscle tissues, the cycle of contraction-relaxation is mainly regulated by the cytosolic Ca, and many other factors, such as substances released from endothelial cells and perivascular nerve terminals (mainly sympathetic nerves). In this article, we introduce regional differences in specific features of ionic channels in vascular smooth muscle membranes (mainly on features of Ca, Na and K channels) in relation to mobilization of the cytosolic Ca. In many vascular tissues, neurotransmitters released from sympathetic nerve terminals activate post-junctional receptors, and subsequently modify ion channels (receptor-activated cation channel and voltage-dependent Ca channel), whereas in some tissues, ionic channels are not modified by receptor activations (pharmaco-mechanical coupling). However, activation of receptors, with or without modulation of ionic channels, regulates the cytosolic Ca through synthesis of second messengers. In addition, receptors distributed on prejunctional nerve terminals positively or negatively regulate the release of transmitters. Roles of neurotransmitters (mainly ATP and noradrenaline) are also discussed in relation to the generation of excitatory junction potentials.     

神经营养因子对神经肌肉接头传递的调制作用

运动单位由运动神经元及其支配的肌纤维组成。神经肌肉接头(neuromuscular junction,NMJ)传递受到严密的调节,因而能和运动单位的活动协调一致。在NMJ,神经调制物质的释放与运动单位的活动有关,并能决定突触传递的效能。脑源性神经营养因子(brain—derived neurotrophic factor,BDNF)和神经营养因子4(neurotrophin-4,NT-4)由运动神经末梢和肌纤维产生。肌肉释放营养因子受肌肉活动调节。在NMJ,BDNF和NT-4通过激活酪氨酸激酶B受体(tyrosine kinase receptor B,TrkB),能加强自发性和诱导性的突触活动。突触前Ca^2 量的迅速增加或突触胞吐过程的易化,都能增加突触囊泡的释放,从而改善NMJ的突触传递。事实上,BDNF能促进突触前细胞内Ca^2 的释放,TrkB的激活也能通过有丝分裂活化蛋白激酶,引起突触素I(synapsinI)的磷酸化,进而增加可释放的突触囊泡的数量。在NMJ,神经营养因子还能通过影响神经调节素(neuregulin)或其他神经源性调制物质的局部释放,对接头传递进行调节。本文对近年来在NMJ突触传递的调节,运动单位的NMJ特性以及神经营养因子对突触传递效能的影响等方面的研究进展做一综述。     

Pre- and post-synaptic actions of memantine at cholinergic central synapse of Achatina fulica

The effects of memantine, an anticonvulsant, on (1) postsynaptic currents (PSC), (2) the responses to microperfused acetylcholine (ACh) and (3) Ca-currents were studied at voltage-clamped identified Lp10 neuron of Achatina fulica. Memantine (5.58 μM) evoked PSCs; however, it did not affect responses of Lp 10 neuron to microperfused ACh. PSCs evoked by memantine were blocked by d-tubocurarine (d-Tc) and removed in low Ca²⁺-high Mg²⁺ solutions. Memantine did not evoke PSCs if the same neurone was physically isolated. The PSCs evoked by memantine and microperfusion of ACh opened the same Cl-currents and both currents were blocked by d-Tc. Memantine increased the amplitude of the voltage-activated Ca-current at the neurones neighborhood to Lp10 neuron by 43±7%. Flunarizine (10 μM), a Ca channel antagonist, decreased 66±5% of the amplitude of Ca current and it also prevented memantine-induced PSCs. The amplitude of responses to microperfused ACh was not affected by flunarizine. These results suggest that memantine triggers the release of ACh at this synapse and this effect of memantine seems to be secondary to memantine-induced increase of Ca²⁺ entry through voltage activated Ca channels.     

Pre- and post-synaptic activity of glutamate on preparations of the frog semicircular canal

Glutamate (Glu) has at least two sites of action in the frog semicircular canal: the hair cell (presynaptic) and the primary afferent nerve fibres (postsynaptic). Glu's action on the hair cell results in an increased release of the natural transmitter which is responsible for a substantial increase in the frequency of firing in primary afferents. Glu produces a long-lasting depolarization in the afferent nerve fibres which does not by itself elicit any afferent discharge of impulses when the release of the natural transmitter is prevented. The difficulty of reconciling some of the observations made of the effects of Glu in semicircular canals with its presumed role as an afferent transmitter in this organ is discussed.