The Journal of General Physiology, Vol 81, 571-588, Copyright © 1983 by The Rockefeller University Press
Comparison of excitatory currents activated by different transmitters on crustacean muscle. II. Glutamate-activated currents and comparison with acetylcholine currents present on the same muscle
C Lingle and A Auerbach
The properties of glutamate-activated excitatory currents on the gm6 muscle
from the foregut of the spiny lobsters Panulirus argus and interruptus and
the crab Cancer borealis were examined using either noise analysis,
analysis of synaptic current decays, or slow iontophoretic currents. The
properties of acetylcholine currents activated in nonjunctional regions of
the gm6 muscle were also examined. At 12 degrees C and -80 mV, the
predominant time constant of power spectra from glutamate-activated current
noise was approximately 7 ms and the elementary conductance was
approximately 34 pS. At 12 degrees C and -80 mV, the predominant time
constant of acetylcholine- activated channels was approximately 11 ms with
a conductance of approximately 12 pS. Focally recorded glutamatergic
extracellular synaptic currents on the gm6 muscle decayed with time
constants of approximately 7-8 ms at 12 degrees C and -80 mV. The decay
time constant was prolonged e-fold about every 225-mV hyperpolarization in
membrane potential. The Q10 of the time constant of the synaptic current
decay was approximately 2.6. The voltage dependence of the steady-state
conductance increase activated by iontophoretic application of glutamate
has the opposite direction of the steady-state conductance activated by
cholinergic agonists when compared on the gm6 muscles. The
glutamate-activated conductance increase is diminished with
hyperpolarization. The properties of the marine crustacean glutamate
channels are discussed in relation to glutamate channels in other organisms
and to the acetylcholine channels found on the gm6 muscle and the gm1
muscle of the decapod foregut (Lingle and Auerbach, 1983).
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