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Frog Neuromuscular Junction (frog + neuromuscular_junction)
Selected AbstractsThe Effect of Carbachol and ,-Bungarotoxin on the Frequency of Miniature Endplate Potentials at the Frog Neuromuscular JunctionEXPERIMENTAL PHYSIOLOGY, Issue 2 2000Ela Bukharaeva The effects of an acetylcholine analogue, carbachol (CCh), and a purified irreversible nicotinic antagonist, ,-bungarotoxin (BTX), on the frequency of the miniature endplate potentials (mEPPs) at the neuromuscular junction of the frog were tested at 20 and 10°C. CCh (5 ± 10-6 m) reduced the frequency of mEPPs to about 60%; this reduction was not affected by 1 ± 10-7 g ml-1 BTX. BTX also reversibly decreased the mEPP frequency by 40%, but not in the presence of CCh or in Ringer solution with 0 or 8 mM Ca2+. The present data show that BTX, which inhibits a class of nicotinic ACh receptors, does not block the decrease of mEPP frequency evoked by CCh and can itself suppress the frequency of spontaneous quantal release. [source] Negative cross-talk between presynaptic adenosine and acetylcholine receptorsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 1 2006A. V. Shakirzyanova Abstract Functional interactions between presynaptic adenosine and acetylcholine (ACh) autoreceptors were studied at the frog neuromuscular junction by recording miniature end-plate potentials (MEPPs) during bath or local application of agonists. The frequency of MEPPs was reduced by adenosine acting on presynaptic adenosine A1 receptors (EC50 = 1.1 µm) or by carbachol acting on muscarinic M2 receptors (EC50 = 1.8 µm). However, carbachol did not produce the depressant effect when it was applied after the action of adenosine had reached its maximum. This phenomenon implied that the negative cross-talk (occlusion) had occurred between A1 and M2 receptors. Moreover, the occlusion was receptor-specific as ATP applied in the presence of adenosine continued to depress MEPP frequency. Muscarinic antagonists [atropine or 1-[[2-[(diethylamino)methyl)-1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido [2,3-b][1,4]benzodiazepine-6-one) (AFDX-116)] had no effect on the inhibitory action of adenosine and adenosine antagonists [8-(p -sulfophenyl)theophylline (8-SPT) or 1,3-dipropyl-8-cyclopentylxanthine (DPCPX)] had no effect on the action of carbachol. These data suggested that membrane,delimited interactions did not occur between A1 and M2 receptors. Both carbachol and adenosine similarly inhibited quantal release triggered by high potassium, ionomycin or sucrose. These results indicated a convergence of intracellular pathways activated by M2 and A1 receptors to a common presynaptic effector located downstream of Ca2+ influx. We propose that the negative cross-talk between two major autoreceptors could take place during intense synaptic activity and thereby attenuate the presynaptic inhibitory effects of ACh and adenosine. [source] Mechanisms of ATP action on motor nerve terminals at the frog neuromuscular junctionEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2005S. Grishin Abstract We have shown previously that ATP inhibits transmitter release at the neuromuscular junction through the action on metabotropic P2Y receptors coupled to specific second messenger cascades. In the present study we recorded K+ or Ca2+ currents in motor nerve endings or blocked K+ or Ca2+ channels in order to explore the nature of downstream presynaptic effectors. Endplate currents were presynaptically depressed by ATP. Blockers of Ca2+ -activated K+ -channels, such as iberiotoxin, apamin or tetraethylammonium, did not change the depressant action of ATP. By contrast, K+ channel blocker 4-aminopyridine (4-AP) and raised extracellular Ca2+ attenuated the effect of ATP. However, these effects of 4-AP and high Ca2+ were reversed by Mg2+, suggesting Ca2+ -dependence of the ATP action. Ba2+ promoted the depressant action of ATP as did glibenclamide, a blocker of ATP-sensitive K+ channels, or mild depolarization produced by 7.5 mm K+. None of the K+ channel blockers affected the depressant action of adenosine. Focal recording revealed that neither ATP nor adenosine affected the fast K+ currents of the motor nerve endings. However, unlike adenosine, ATP or UTP, an agonist of P2Y receptors, reversibly reduced the presynaptic Ca2+ -current. This effect was abolished by suramin, an antagonist of P2 receptors. Depressant effect of ATP on the endplate and Ca2+ -currents was mimicked by arachidonate, which precluded the action of ATP. ATP reduced acetylcholine release triggered by ionomycin or sucrose, suggesting inhibition of release machinery. Thus, the presynaptic depressant action of ATP is mediated by inhibition of Ca2+ channels and by mechanism acting downstream of Ca2+ entry. [source] Effects of wortmannin and latrunculin A on slow endocytosis at the frog neuromuscular junctionTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004D. A. Richards Phosphoinositides are key regulators of synaptic vesicle cycling and endocytic traffic; the actin cytoskeleton also seems to be involved in modulating these processes. We investigated the effects of perturbing phosphoinositide signalling and actin dynamics on vesicle cycling in frog motor nerve terminals, using fluorescence and electron microscopy, and electrophysiology. Antibody staining for ,-actin revealed that actin surrounds but does not overlap with synaptic vesicle clusters. Latrunculin A, which disrupts actin filaments by binding actin monomers, and wortmannin, an inhibitor of phosphatidyl inositol-3-kinase (PI3-kinase), each disrupted the pattern of presynaptic actin staining, but not vesicle clusters in resting terminals. Latrunculin A, but not wortmannin, also reduced vesicle mobilization and exocytosis. Both drugs inhibited the stimulation-induced uptake of the styryl dye FM1-43 and blocked vesicle reformation from internalized membrane objects after tetanic stimulation. These results are consistent with a role of PI3-kinase and the actin cytoskeleton in the slow pathway of vesicle endocytosis, used primarily by reserve pool vesicles. [source] | ||||||||||