Article Information

• PDF (1510 kb)

PubMed

• Articles by Y. Yuan
• Articles by D. Axelrod

Related Articles

• Localized Acetylcholine Receptor Clustering Dynamics in Resp...

  Localized Acetylcholine Receptor Clustering Dynamics in Response to Microfluidic Focal Stimulation with Agrin Biophysical Journal, Volume 95, Issue 6, 15 September 2008, Pages 3009-3016 Anna Tourovskaia, Nianzhen Li and Albert Folch Abstract Agrin is a proteoglycan secreted by the motor neuron's growing axon terminal upon contact with the muscle during embryonic development. It was long thought that agrin's role was to trigger the clustering of acetylcholine receptors (AChRs) to nascent synapse sites. However, agrin-predating, protosynaptic AChR clusters are present well before innervation in the embryo and in myotube cultures, yet no role has been conclusively ascribed to agrin. We used a microfluidic device to focally deliver agrin to protosynaptic AChR clusters in micropatterned myotube cultures. The distribution of AChRs labeled with fluorescent bungarotoxin was imaged at various time points over >24h. We find that a 4-h focal application of agrin (100 nM) preferentially reduces AChR loss at agrin-exposed clusters by 17% relative to the agrin-deprived clusters on the same myotube. In addition, the focal application increases the addition of AChRs preferentially at the clusters by 10% relative to the agrin-exposed, noncluster areas. Taken together, these findings suggest that a focal agrin stimulus can play a key stabilizing role in the aggregation of AChRs at the early stages of synapse formation. This methodology is generally applicable to various developmental processes and cell types, including neurons and stem cells. Abstract | Full Text | PDF (327 kb)

• Gating current kinetics in Myxicola giant axons. Order of th...

  Gating current kinetics in Myxicola giant axons. Order of the back transition rate constants Biophysical Journal, Volume 59, Issue 3, 1 March 1991, Pages 574-589 L. Goldman Abstract Gating current, Ig, was recorded in Myxicola axons with series resistance compensation and higher time resolution than in previous studies. Ig at ON decays as two exponentials with time constants, tau ON-F and tau ON-S, very similar to squid values. No indication of an additional very fast relaxation was detected, but could be still unresolved. Ig at OFF also displays two exponentials, neither reflecting recovery from charge immobilization. Deactivation of the two I(ON) components may proceed with well-separated exponentials at -100 mV. INa tail currents at OFF also display two exponentials plus a third very slow relaxation of 5–9% of the total tail current. The very slow component is probably deactivation of a very small subpopulation of TTX sensitive channels. A -100 mV, means for INa tail component time constants (four axons) are 76 microseconds (range: 53–89 microseconds) and 344 microseconds (range: 312–387 microseconds), and for IOFF (six axons) 62 microseconds (range: 34–87 microseconds) and 291 microseconds (range: 204–456 microseconds) in reasonable agreement. INa ON activation time constant, tau A, is clearly slower than tau ON-F at all potentials. Except for the interval -30 to -15 mV, tau A is clearly faster than tau ON-S, and has a different dependency on potential. tau ON-S is several fold smaller than tau h. Computations with a closed2----closed1----open activation model indicated Na tail currents are consistent with a closed1----open rate constant greater than the closed2----closed1. Abstract | PDF (1657 kb)

• Challenging the Neurocentric View of Neuromuscular Synapse F...

  Challenging the Neurocentric View of Neuromuscular Synapse Formation Neuron, Volume 30, Issue 2, 1 May 2001, Pages 311-314 Michael Ferns and Salvatore Carbonetto Full Text | PDF (134 kb)

• …more

Abstract

Polarized fluorescence recovery after photobleaching (PFRAP) is a technique for measuring the rate of rotational motion of biomolecules on living, nondeoxygenated cells with characteristic times previously ranging from milliseconds to many seconds. Although very broad, that time range excludes the possibility of quantitatively observing freely rotating membrane protein monomers that typically should have a characteristic decay time of only several microseconds. This report describes an extension of the PFRAP technique to a much shorter time scale. With this new system, PFRAP experiments can be conducted with sample time as short as 0.4 microseconds and detection of possible characteristic times of less than 2 microseconds. The system is tested on rhodamine-alpha-bungarotoxin-labeled acetylcholine receptors (AChRs) on myotubes grown in primary cultures of embryonic rat muscle, in both endogenously clustered and nonclustered regions of AChR distribution. It is found that approximately 40% of the AChRs in nonclustered regions undergoes rotational diffusion fast enough to possibly arise from unrestricted monomer Brownian motion. The AChRs in clusters, on the other hand, are almost immobile. The effects of rat embryonic brain extract (which contains AChR aggregating factors) on the myotube AChR were also examined by the fast PFRAP system. Brain extract is known to abolish the presence of endogenous clusters and to induce the formation of new clusters. It is found here that rotational diffusion of AChR in the extract-induced clusters is as slow as that in endogenous clusters on untreated cells but that rotational diffusion in the nonclustered regions of extract-treated myotubes remains rapid.