The influence of the plant lectin Concanavalin A (ConA) on the properties of membrane channels opened by 25-200 microM-L-glutamate in voltage-clamped locust muscle fibres has been studied. Power spectral density plots of membrane current fluctuations were used to estimate the mean lifetime and conductance of glutamate-induced channels. 2. Exposure to ConA (10 micrograms/ml.) increased the amplitude of the mean current evoked by 200 microM-glutamate from 7.7 +/- 4.7 nA (mean +/- S.D.) to 81 +/- 57 nA (membrane potential -60 mV, temperature 16 degrees C). The mean conductance of glutamate-induced channels (65 +/- 16.8 pS at 16 degrees C) was negligibly affected by the lectin. 3. In normal saline the mean lifetime of glutamate-induced channels tau noise decreased on membrane hyperpolarization. After treatment with ConA (70 micrograms/ml.), tau noise become totally independent of membrane voltage when studied at potentials in the range -60 to -120 mV. The value of tau noise at the resting potential was little altered by the lectin.
