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

Abstract

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°C and -80 mV, the predominant time constant of power spectra from glutamate-activated current noise was ~7 ms and the elementary conductance was ~34 pS. At 12°C and -80 mV, the predominant time constant of acetylcholine-activated channels was ~11 ms with a conductance of ~12 pS. Focally recorded glutamatergic extracellular synaptic currents on the gm6 muscle decayed with time constants of ~7-8 ms at 12°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 ~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 gml muscle of the decapod foregut (Lingle and Auerbach, 1983). © 1983, Rockefeller University Press., All rights reserved.