Abstract
The temperature dependence of miniature endplate current (MEPC) amplitude
(A(c)), 20-80\% rise time (t(r)), and 90-33\% fall-time (t(f)) was
determined for lizard (Anolis carolinensis) intercostal muscle using
broadband extracellular (EC) and voltage clamp (VC) recordings. Voltage
clamp methods were optimized for the fast MEPC rising phase using
custom electronics. From 0-43 degrees C, A(c) increased by approximately
4.2-fold, while t(r) and t(f) decreased by approximately 3.6- and
approximately 9.5-fold, respectively. Arrhenius plots were smoothly
curved, with small apparent Q(10) (A(c)) or (Q(10))(-1) (t(r) and
t(f)) values mostly well below 2.0. Nearly identical extracellular
and voltage clamp results ruled out measurement artifacts, even for
the shortest t(r) values (<60 microseconds). Monte Carlo simulation
of MEPCs showed that a single underlying rate cannot determine the
observed temperature dependence. To quantitatively reproduce the
experimental t(f) results, a minimal model required activation energies
of 46.0 (Q(10) approximately 2.0) and 63.6 (Q(10) approximately 2.5)
kJ mol(-1) for channel opening and closing, respectively, and accounted
for most of the observed changes in A(c) and t(r) as well. Thus,
relatively large but offsetting temperature sensitivities of channel
gating mostly govern and minimize the temperature dependence of MEPCs,
preserving the safety factor for neuromuscular transmission. Additional
temperature-sensitive parameters that could fine-tune the minimal
model are discussed.
- 10423463
- acetylcholinesterase,
- al,
- animals,
- biophysics,
- carlo
- channel
- cholinergic,
- computer
- endplate,
- gating,
- gov't,
- in
- intercostal
- ion
- lizards,
- method,
- models,
- monte
- motor
- muscles,
- neurologic,
- non-p.h.s.,
- non-u.s.
- p.h.s.,
- patch-clamp
- receptors,
- research
- simulation,
- support,
- synaptic
- techniques,
- temperature,
- transmission,
- u.s.
- vitro,
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