1,721,057 research outputs found
Prostaglandin E2 Stimulates Fibronectin Expression through EP1 Receptor, Phospholipase C, Protein Kinase Cα, and c-Src Pathway in Primary Cultured Rat Osteoblasts
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Nerve Terminal Currents Induced by Autoreception of Acetylcholine Release
No full textThe activation of autoreceptors is known to be important in the modulation of presynaptic transmitter secretion in peripheral and central neurons. Using whole-cell recordings made from the free growth cone of myocyte-contact motoneurons of Xenopus cell cultures, we have observed spontaneous nerve terminal currents (NTCs). These spontaneous NTCs are blocked by d-tubocurarine (d-TC) and - bungarotoxin (-BuTx), indicating that endogenously released acetylcholine (ACh) can produce substantial membrane depolarization in the nerve terminals. Local application of NMDA to the growth cone increased the frequency of spontaneous NTCs. When the electrical stimulations were applied at the soma to initiate evoked- release of ACh, evoked ACh-induced potentials were recorded in the nerve terminals, which were inhibited by d-TC and hexamethonium but not by atropine. Replacement of normal Ringer's solution with high-Mg2+, low-Ca2+ solution also reversibly inhibited evoked ACh-induced potentials. The possible regulatory role of presynaptic nicotinic autoreceptors on the synaptic transmission was also examined. When the innervated myocyte was whole-cell voltage-clamped to record synaptic currents, application of hexamethonium inhibited the amplitude of evoked synaptic currents at a higher degree than that of iontophoretic ACh-induced currents. Furthermore , hexamethonium markedly reduced the frequency of spontaneous synaptic currents at high-activity synapses. Pretreatment of neurons with -BuTx also inhibited the evoked synaptic currents in manipulated synapses. These results suggest that ACh released spontaneously or by electrical stimulation may act on the presynaptic nicotinic autoreceptors of the same nerve terminals to produce membrane potential change and to regulate synaptic transmission
Regulation of Presynaptic Nmda Responses by External and Intracellular Ph Changes at Developing Neuromuscular Synapses
No full textNMDA receptors play important roles in synaptic plasticity and neuronal development. The functions of NMDA receptors are modulated by many endogenous substances, such as external pH (pHe), as well as second messenger systems. In the present study, the nerve-muscle cocultures of Xenopus embryos were used to investigate the effects of both external and intracellular pH (pHi) changes on the functional responses of presynaptic NMDA receptors. Spontaneous synaptic currents (SSCs) were recorded from innervated myocyte using whole-cell recordings. Local perfusion of NMDA at synaptic regions increased the SSC frequency via the activation of presynaptic NMDA receptors. A decrease in pHe from 7.6 to 6.6 reduced NMDA responses to 23% of the control, and an increase in pHe from 7.6 to 8.6 potentiated the NMDA responses in increasing SSC frequency. The effect of NMDA on intracellular Ca2+ concentration ([Ca2 +]i) was also affected by pHe changes: external acidification inhibited and alkalinization potentiated [Ca2+ ]i increases induced by NMDA. Intracellular pH changes of single soma were measured by ratio fluorometric method using 2,7-bis ( carboxyethyl)-5,6-carboxyfluorescein (BCECF). Cytosolic acidification was used in which NaCl in Ringer's solution was replaced with weak organic acids. Acetate and propionate but not methylsulfate substitution caused intracellular acidification and potentiated NMDA responses in increasing SSC frequency, intracellular free Ca2+ concentration, and NMDA-induced currents. On the other hand, cytosolic alkalinization with NH4Cl did not significantly affect these NMDA responses. These results suggest that the functions of NMDA receptors are modulated by both pHe and pHi changes, which may occur in some physiological or pathological conditions
Studies on Neuromuscular Blockade by Boldine in the Mouse Phrenic Nerve- Diaphragm
No full textThe effects of boldine [(S)-2, 9-dihydroxyl-1, 10-dimethoxy- aporphine], a major alkaloid in the leaves and bark of Boldo(Peumus boldus Mol.), on neuromuscular transmission were studied using a muscle phrenic-nerve diaphragm preparation. Boldine at concentrations lower than 200 μM preferentially inhibited, after an initial period of twitch augmentation, the nerve-evoked twitches of the mouse diaphragm and left the muscle- evoked twitches unaffected. The twitch inhibition could be restored by neostigmine or washout with Krebs solution. The twitches evoked indirectly and directly were both augmented initially, suggesting that the twitch augmentation induced by boldine was myogenic. Boldine inhibited the acetylcholine-induced contraction of denervated diaphragm dose-dependently with an IC50 value of 13.5 μM. At 50 μM, boldine specifically inhibited the amplitude of the miniature end plate potential. In addition, boldine was similar to d-tubocurarine in its action to reverse the neuromuscular blocking action of α-bungarotoxin . These results showed that the neuromuscular blockade by boldine on isolated mouse phrenic-nerve diaphragm might be due to its direct interaction with the postsynaptic nicotinic acetylcholine receptor
Potentiation by ATP of the postsynaptic acetylcholine response at developing neuromuscular synapese in Xenopus cell cultures
No full text 1. Extracellular application of ATP to developing Xenopus neuromuscular synapses in culture resulted in a marked increase in the amplitude and frequency of spontaneous synaptic currents, using whole-cell recorking. 2. The postsynaptic action of ATP was examined by studying the response of isolated muscle cells to iontophoretically spplied acetylcholine (ACh). ATP enhanced the responses of the muscle membrane to ACh. The order of poteney for various nucleotides (ATP=ADP》AMP, adenosine , GTP) suggests that ATP acts through P2-purinoceptors. The effect of ATP on whole-cell currents was also abolished by the protein dinase inhibitor H-7. 3. Single-channel measurements indicate that ATP increased the mean open time of low-conductance ACh channels. No change in the conductance of ACh channels was observed. 4. Local application of ATP to one region of the elongated myocyte surface resulted in potentiated ACh responses only at the ATP-treated region, suggesting that the eytosolic second messengers were effectively confined within the muscle cytoplasm. 5. The results of the present study suggest that ATP released from the nerve terminals may potentiate the ACh response of developing muscle cells during the early phase of synaptogenesis, and that the action of ATP can be restricted to the subsynaptic region exposed to the secreted ATP.#0839
Regulation of Acetylcholine Release by Extracellular Matrix Proteins at Developing Motoneurons in Xenopus Cell Cultures
No full textIntegrins mediate cell-extracellular matrix connections and are particularly important during neuronal development. We here investigated the regulatory role of extracellular matrix (ECM) proteins on the synaptic transmission at developing motoneurons. Synaptic currents were recorded from innervated myocytes of 1-day-old Xenopus cultures by whole- cell recordings. Soluble fibronectin and laminin had no significant effect on the frequency of spontaneous synaptic currents (SSCs) by themselves and markedly increased SSC frequency in the presence of low concentration of protein kinase C (PKC) activators. Pretreatment with Gly-Arg-Gly-Asp -Ser peptide inhibited the SSC increasing action of 12-o- tetradecanoyl-phorbol -13-acetate (TPA, 0.5 M) plus fibronectin, but not that of TPA plus laminin. Genistein but not cytochalasin D inhibited the SSC increasing action of TPA plus fibronectin or laminin. High concentration of TPA ( 5 M ) markedly increased the SSC frequency by itself and occluded the SSC increasing action of fibronectin. Very low concentration of TPA (0.05 M) markedly enhanced the SSC frequency when the cells were plated onto fibronectin- or laminin-coated substratum for 1 day. The SSC frequency increased markedly right after a train stimulation, which was defined as post-train potentiation (PTrP), when the cultures were plated onto fibronectin substratum and chronically treated with brain-derived neurotrophic factor ( BDNF). The PTrP phenomenon is not observed upon chronic treatment with neurotrophin-3, glial cell line-derived neurotrophic factor, or ciliary neurotrophic factor. Our results suggest that the activation of PKC and tyrosine kinase but not actin reorganization plays a role in the SSC potentiating action of fibronectin. BDNF exerts synergistic effects in increasing synaptic transmission in neurons grown on fibronectin substratum. ECMs in concert with neurotrophic factor may play a role in regulating synaptic function at developing motoneurons
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