Glutamate activated postsynaptic channels in crayfish muscle investigated by noise analysis

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Abstract
Excitatory synaptic channels in crayfish muscle were investigated under various experimental conditions. Small muscle fibres of lengthl≤0.6 mm were voltage clamped, spatial control of the voltage being sufficient up to at least 500 Hz. Excitatory synaptic current was induced by superfusion of glutamate. The power density spectra of this current could be fitted by single component Lorentz curves. The analysis revealed a mean open time τnoise= 0.93 ms and a conductance γ=32.2 pS of the glutamate operated ion channels (membrane potentialE=−60mV, temperatureT=8°C). Both the conductance γ and the channel closing rate α=τ noise −1 increased significantly with temperature (Q10∼2). The temperature dependence of γ and α could be described by Arrhenius equations with the temperature independent activation energiesE γ=42.3 kJ/mol andE α=50.2 kJ/mol. α also depended on the membrane potential, increasing about e-fold when the membrane was hyperpolarized by 120 mV. The potential dependence varied considerably from fibre to fibre. The mean channel open time τnoise agreed with the time constant of decay τ(sEPSC) of spontaneous excitatory postsynaptic currents (sEPSCs).

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