Effects of concanavalin A on glutamate operated postsynaptic channels in crayfish muscle

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Abstract
Small crayfish muscle fibres were voltage clamped, and synaptic current noise induced by bath application of glutamate was measured. Desensitization of the glutamate receptors was blocked by preincubating the fibres with 0.3–1.0 μmol/l concanavalin A (Con A) for at least 30 min. The power density spectra of the glutamate current noise could be fitted by single component Lorentz curves. The lectin Con A did not influence significantly the conductance γ of the glutamate channels but increased their mean open time, τnoise. The respective mean values found atT=8°C andE=−60 mV were γ=23.5±7.0 pS and τnoise=1.5 ±0.2 ms. Both the conductance γ and the closing rate α = τ noise −1 increased with temperature (Q10∼1.9). This temperature dependence was characterized by the activation energies Eγ=35.2±7.1 kJ/mol andE α=46.9±2.1 kJ/mol. The potential dependence of τnoise was almost completely abolished by Con A.