The Journal of General Physiology, Vol 75, 297-321, Copyright © 1980 by The Rockefeller University Press
Acetylcholine-induced current in perfused rat myoballs
R Horn and MS Brodwick
Spherical "myoballs" were grown under tissue culture conditions from
striated muscle of neonatal rat thighs. The myoballs were examined
electrophysiologically with a suction pipette which was used to pass
current and perfuse internally. A microelectrode was used to record
membrane potential. Experiments were performed with approximately
symmetrical (intracellular and extracellular) sodium aspartate solutions.
The resting potential, acetylcholine (ACh) reversal potential, and sodium
channel reversal potential were all approximately 0 mV. ACh-induced
currents were examined by use of both voltage jumps and voltage ramps in
the presence of iontophoretically applied agonist. The voltage-jump
relaxations had a single exponential time-course. The time constant, tau,
was exponentially related to membrane potential, increasing e-fold for 81
mV hyperpolarization. The equilibrium current- voltage relationship was
also approximately exponential, from -120 to +81 mV, increasing e-fold for
104 mV hyperpolarization. The data are consistent with a first-order gating
process in which the channel opening rate constant is slightly voltage
dependent. The instantaneous current-voltage relationship was sublinear in
the hyperpolarizing direction. Several models are discussed which can
account for the nonlinearity. Evidence is presented that the "selectivity
filter" for the ACh channel is located near the intracellular membrane
surface.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
