The Journal of General Physiology, Vol 81, 547-569, Copyright © 1983 by The Rockefeller University Press
Comparison of excitatory currents activated by different transmitters on crustacean muscle. I. Acetylcholine-activated channels
C Lingle and A Auerbach
The properties of acetylcholine-activated excitatory currents on the gm1
muscle of three marine decapod crustaceans, the spiny lobsters Panulirus
argus and interruptus, and the crab Cancer borealis, were examined using
either noise analysis, analysis of synaptic current decays, or analysis of
the voltage dependence of ionophoretically activated cholinergic
conductance increases. The apparent mean channel open time (tau n) obtained
from noise analysis at -80 mV and 12 degrees C was approximately 13 ms; tau
n was prolonged e-fold for about every 100-mV hyperpolarization in membrane
potential; tau n was prolonged e- fold for every 10 degrees C decrease in
temperature. Gamma, the single- channel conductance, at 12 degrees C was
approximately 18 pS and was not affected by voltage; gamma was increased
approximately 2.5-fold for every 10 degrees C increase in temperature.
Synaptic currents decayed with a single exponential time course, and at -80
mV and 12 degrees C, the time constant of decay of synaptic currents, tau
ejc, was approximately 14-15 ms and was prolonged e-fold about every 140-mV
hyperpolarization; tau ejc was prolonged about e-fold for every 10 degrees
C decrease in temperature. The voltage dependence of the amplitude of
steady-state cholinergic currents suggests that the total conductance
increase produced by cholinergic agonists is increased with
hyperpolarization. Compared with glutamate channels found on similar
decapod muscles (see the following article), the acetylcholine channels
stay open longer, conduct ions more slowly, and are more sensitive to
changes in the membrane potential.
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