Na⁺ current in presynaptic terminals of the crayfish opener cannot initiate action potentials

Abstract

Lin JW. Na ϩ current in presynaptic terminals of the crayfish opener cannot initiate action potentials.

Focused ultrasound transiently increases membrane conductance in isolated crayfish axon

“…To gain a better understanding of mechanisms of USmediated neuromodulation, we studied the biophysical effects of focused US on single motor axons of the crayfish opener neuromuscular junction (Lin 2008(Lin , 2012(Lin , 2013(Lin , 2016. We found two novel phenomena produced by a focused US tone burst in this preparation.…”

“…VGCs appeared to play a minimal role in US-induced depolarization, since it was still detectable after the main VGCs in this preparation were blocked. Specifically, 1 M TTX, which blocks sodium channels, 200 M 4-AP, which blocks the dominant low-threshold potassium channels, and 50 M ZD7288, which blocks hyperpolarization-activated cation channels, were used to block the main VGCs previously described in the axons (Beaumont and Zucker 2000;Lin 2008Lin , 2012Lin , 2013Lin , 2016. Calcium channels were not blocked because they had been shown to localize in terminal varicosities and to contribute minimally to AP waveform recorded in the axon (Delaney et al 1991;Wojtowicz and Atwood 1984).…”

“…The axons are large and allow for two-electrode current clamp from two locations simultaneously (Lin 2008(Lin , 2012. These technical advantages have been exploited to demonstrate that Na ϩ , Ca 2ϩ , and 4-aminopyridine (4-AP)-sensitive K ϩ channels have nonuniform densities along the proximo-distal axis (Delaney et al 1991;Lin 2012Lin , 2013Lin , 2016. The preparation is hardy and allows for stable intracellular recordings for up to 36 h (Lin 2008).…”

Effects of levetiracetam on axon excitability and synaptic transmission at the crayfish neuromuscular junction

“…Previous studies on motor axons of the opener preparation have suggested spatial inhomogeneity of Na + and K + channel densities along the proximo‐distal axis. It has been reported that tetrodotoxin at 1 nM preferentially reduces the excitability of distal branches (Lin, 2013) and that terminal varicosities cannot fire APs by local current injection (Lin, 2016). Furthermore, a 4‐AP sensitive, low voltage‐activated K + channel is concentrated in distal branches, where it is essential for shaping AP amp and duration (Lin, 2012).…”

“…If vesicular recycling is the main entry path for LEV, and if the antiepileptic effects of this drug include its actions on ion channels, then, axon excitability should be the first neuronal compartment affected. The opener motor axons of crayfish are accessible to intracellular recording from multiple locations simultaneously, and are ideal for detailed examination of the spatial and temporal factors that contribute to modulation of axonal excitability (Lin, 2012, 2013, 2016). Here, we report the effects of LEV on motor axon excitability and synaptic transmission in the opener preparation.…”