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Journal Article↗
Biomedical subjects
J C Liou
Publications and source records attributed to J C Liou.
Target-dependent regulation of acetylcholine secretion at developing motoneurons in Xenopus cell cultures.
1. Myocyte-dependent regulation of acetylcholine (ACh) quantal secretion from developing motoneurons was studied in day-3 Xenopus nerve-muscle co-cultures. Spontaneous synaptic currents (SSCs) were measured in manipulated synapses by using whole-cell voltage-clamped myocytes. Changes in SSC amplitude were assumed to reflect changes in the ACh content of secreted quantal packets. Compared with natural synapses, motoneurons without any contact with a myocyte (naive neurons) released ACh in smaller quantal packets. 2. Bipolar cultured motoneurons, which were in contact with a myocyte with one axon branch (contact-end) but remained free at another axon branch (free-end), were further used to examine quantal ACh secretion. The ACh quantal size recorded at free-end terminals was similar to that of naive neurons and was smaller than that at the contact-end, indicating that myocyte contact exerts differential regulation on quantal secretion in the same neuron. 3. Some of the neurons that formed a natural synapse with a myocyte continued to grow forward and ACh quantal secretion from the free growth cone was examined. The ACh quantal size recorded at free growth cones was inversely proportional to the distance to the natural synapse, implying localized regulation of quantal secretion by the myocyte. 4. Chronic treatment of day-1 cultures with veratridine and d-tubocurarine, respectively, increased and decreased the neurotrophic action of myocytes when assayed on day 3. 5. Taken together, these findings suggest that the myocyte is an important postsynaptic target in the regulation of quantal secretion and that the trophic action is spatially restricted to the neighbourhood of the neuromuscular junction.
Acetylcholine↗
Regulation of quantal secretion by neurotrophic factors at developing motoneurons in Xenopus cell cultures.
1. The ability of different neurotrophic factors to maintain and regulate synaptic function at the developing motoneuron was studied in Xenopus nerve-muscle co-cultures. Spontaneous synaptic currents (SSCs) were measured by using whole-cell voltage-clamped myocytes. 2. Compared with natural synapses, motoneurons without contact on a myocyte (naive neurons) released ACh in smaller quantal packets, the amplitude being inversely proportional to the days in culture. The mean SSC amplitudes of naive neurons, which were measured by manipulating a myoball into contact with the myocyte-free nerve terminals to form a manipulated synapse, were 99.5 +/- 6.7 and 48.2 +/- 1.9 pA for day-1 and day-3 cultures, respectively. 3. Chronic treatment of day-1 cultures with brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), neurotrophin-4 (NT-4), ciliary neurotrophic factor (CNTF) or glial cell line-derived neurotrophic factor (GDNF) for 2 days, increased the ACh quantal size of naive motoneurons in a concentration-dependent manner, whereas insulin-like growth factor-1 (IGF-1) and basic fibroblast growth factor (bFGF) had no effect, even at high concentrations. 4. The interaction of various neurotrophic factors was examined, using concentrations that gave maximal effects. Combination of CNTF plus BDNF or CNTF plus NT-3 had synergistic effects in potentiating SSC amplitude of the manipulated synapse of naive neurons, whereas NT-3 plus BDNF, NT-3 plus GDNF, BDNF plus GDNF or CNTF plus GDNF had no synergistic action. 5. Chronic treatment with d-tubocurarine for 2 days resulted in a reduction of the quantal size of natural synapses. Concomitant treatment with BDNF, NT-3, GDNF, CNTF but not bFGF or IGF-1, reconstituted the SSC amplitude. 6. Taken together, these findings suggest that BDNF, NT-3, NT-4, CNTF and GDNF may regulate and maintain the synaptic function of developing motoneurons, and different neurotrophic factors utilizing distinct signalling mechanisms may have synergistic actions.
Acetylcholine↗
Regulation of quantal secretion from developing motoneurons by postsynaptic activity-dependent release of NT-3.
Neurotrophic factors derived from postsynaptic muscle cells may play important roles in the development of presynaptic neuronal functions. In 3-d-old Xenopus nerve-muscle cultures, embryonic spinal neurons that had made natural contact with co-cultured myocytes exhibited spontaneous release of larger packets of acetylcholine (ACh) quanta than those released by the isolated neurons having no contact with any myocyte. Treatment of isolated neurons with neurotrophin-3 (NT-3) for 2 d increased the average sizes of quantal ACh packets at newly formed nerve-muscle synapses, whereas treatment with antibody against NT-3 or with K252a, a specific inhibitor of tyrosine kinase receptors, decreased the quantal size at existing synapses, which suggests that NT-3 supplied by the postsynaptic muscle cell may be responsible for the development and maintenance of the quantal packets. The muscle effect seems to depend on synaptic activities mediated by postsynaptic ACh receptor channels, because chronic treatment of the culture with D-tubocurarine (D-Tc) for 2 d resulted in a marked reduction of the quantal sizes, when assayed after extensive washing of the culture with Ringer's solution. The curare treatment did not affect the postsynaptic ACh receptor sensitivity, because iontophoretically applied ACh induced current responses similar to those of control. Finally, co-treatment of the culture with NT-3 and D-Tc reversed the effect of D-Tc on the quantal size, and this reversal effect was abolished when K252a was also applied concomitantly. Our results suggest that muscle-derived NT-3 participates in the maturation of normal transmitter packets in developing neurons, and the secretion of NT-3 depends on spontaneous synaptic activity.
Acetylcholine↗
Spontaneous and induced sister chromatid exchanges and delayed cell proliferation in peripheral lymphocytes of Bowen's disease patients and matched controls of arseniasis-hyperendemic villages in Taiwan.
A total of 15 newly-developed Bowen's disease patients and 34 age-sex-residence-matched controls were recruited from three arseniasis-hyperendemic villages in Taiwan to compare spontaneous and arsenic-induced sister chromatid exchanges (SCEs), proportion of cells with high frequencies of SCEs (HFCs), and replication index (RI) in their peripheral lymphocytes. Arsenic-induced Bowen's disease patients were found to have significantly higher spontaneous SCEs and HFCs and a lower spontaneous RI than in matched controls without or with adjustment for age, gender, cigarette smoking, alcohol drinking, tea drinking, status of major diseases, HBsAg carrier status and arsenic exposure indices through multivariate analysis. Sodium arsenite was found to increase SCEs and HFCs and to decrease RI in a dose-response pattern for both cases and controls. The arsenic-induced decrease in RI was significantly greater in arsenic-induced Bowen's disease patients than in matched controls. The arsenic-induced increases in SCEs and HFCs were also consistently, but not statistically significantly, higher in arsenic-induced Bowen's disease patients than in matched controls at all arsenite treatment levels of 0.5, 1.0 and 2.0 microM. The arsenic-induced increase in cytogenetic damages and decrease in cell proliferation among arsenic-induced Bowen's disease patients compared with matched controls may result from their long-term exposure to inorganic arsenic through consumption of high-arsenic artesian well water, elevated individual genetic and acquired susceptibility to arsenic-induced damage, or both.
Arsenic↗
Regulation of quantal transmitter secretion by ATP and protein kinases at developing neuromuscular synapses.
The effects of endogenously released ATP on the maturation of developing neuromuscular synapses were investigated in Xenopus nerve-muscle co-cultures. The potentiating action of ATP (1 mM) on spontaneous acetylcholine release was inhibited by P2-purinoceptor antagonists suramin (0.3 mM) and reactive blue 2 (RB-2, 3 microM) in day 1 cultures. Bath application of suramin (10 microM) or RB-2 in day 1 cultures and prolonged treatment for 2 days dramatically decreased the amplitude of both spontaneous synaptic currents (SSCs) and evoked synaptic currents (ESCs) in the same cultures on day 3. Chronic treatment with 8-cyclopentyltheophylline (4 microM) or 6-cyano-2,3-dihydroxy-7-nitroquinoxaline (CNQX, 10 microM), P1-purinoceptor and glutamate receptor antagonists respectively, did not exert such an inhibitory effect. Chronic treatment with suramin or RB-2 for 2 days had no significant effect on the amplitude of either iontophoretic acetylcholine-induced whole-cell currents or single acetylcholine channel measurements in 3-day-old cultured myocytes. In addition, prolonged treatment for 2 days with various kinase inhibitors such as H-8 (10 microM), KN-62 (5 microM) and H-7 (10 microM) also decreased the amplitudes of both spontaneous and evoked synaptic currents in natural synapses, but not those of iontophoretic acetylcholine-induced currents. Furthermore, suramin and these protein kinase inhibitors also decreased the amplitude of spontaneous synaptic currents in manipulated synapses of 'vacated' nerve terminals. The results suggest that endogenously released ATP, acting in concert with various protein kinases, is involved in the maintenance and/or development of the quantum size of synaptic vesicles at embryonic neuromuscular synapses.
1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
Potentiation of neurotransmitter release by activation of presynaptic glutamate receptors at developing neuromuscular synapses of Xenopus.
1. Glutamate receptors play important roles in synaptic plasticity and neural development. Here we report that, at the developing neuromuscular synapses in Xenopus cultures, the activation of presynaptic glutamate receptors at motor nerve terminals potentiates spontaneous acetylcholine (ACh) release. 2. Co-cultures of spinal neurons and myotomal muscle cells were prepared from 1-day-old Xenopus embryos. Spontaneous synaptic currents (SSCs) were recorded from innervated myocytes using whole-cell recording. Bath application of glutamate (10 microM) markedly increased the frequency of SSCs, and the action of glutamate was reversible. 3. Pretreatment with 0.3 microM tetrodotoxin, which blocks Na+ channels and the conduction of action potentials, only slightly inhibited the potentiating action of glutamate on SSCs. Furthermore, the enhancement of ACh secretion was much more prominent when glutamate was applied locally to the synaptic region. 4. Three types of glutamate receptor agonists, kainate, quisqualate, AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid) and NMDA (N-methyl-D-aspartate), were effective in inducing the potentiating effect. The ranking order was: glutamate > kainate > NMDA > AMPA > quisqualate. Glycine potentiated the effects induced by NMDA. Metabotropic receptors were not involved in the potentiating action of glutamate. 5. The potentiating effect of glutamate depended on the influx of Ca2+ through both L-type Ca2+ channels and NMDA-gated channels. 6. Since glutamate is known to be co-released with ACh at some cholinergic nerve terminals, the released glutamate may serve as a positive feedback regulation of ACh secretion at developing neuromuscular junctions via its action on presynaptic glutamate receptors.
Acetylcholine↗
Additive effect of ADP and CGRP in modulation of the acetylcholine receptor channel in Xenopus embryonic myocytes.
1. We have previously shown that the activation of either protein kinase A (PKA) or protein kinase C (PKC) enhanced the responses of muscle membrane to acetylcholine (ACh) by increasing the mean open time of embryonic-type ACh channels in Xenopus cultured myocytes. In the present study, we further investigated the interaction between these two kinases in the modulation of ACh channels by using the receptor ligands, adenosine diphosphate (ADP) and calcitonin gene-related peptide (CGRP) which selectively activate PKC and PKA, respectively. 2. ADP concentration-dependently increased the mean open time of embryonic-type ACh channels and 0.3 mM ADP is sufficient to achieve the maximal potentiating effect. alpha, beta-Methylene ATP and PMA (phorbol 12-myristate 13-acetate) but not adenosine, AMP, dibutyryl cyclic GMP have similar potentiating action. 3. Suramin (0.3 mM) pretreatment abolished the potentiating effect of ADP but left that of PMA unchanged. 4. CGRP increased the mean open time of embryonic-type ACh channels in a concentration-dependent manner and 1 microM CGRP produced the maximal effect. 5. The maximal effects of both ADP (0.3 mM) and CGRP (1 microM) in the prolongation of mean open time of ACh channels were additive. 6. These results suggest that the modulation of embryonic-type ACh channels by the endogenously released ligands via the activation of PKA and PKC is additive and possibly different sites of ACh channels may be involved in the potentiation effect of either PKC or PKA.
Adenosine Diphosphate↗