Single glutamate-gated synaptic channels at the crayfish neuromuscular junction

Abstract

Single glutamate activated ionic channels were recorded with the patch clamp technique from untreated crayfish muscle fibres with MΩ seals, and after treatment with collagenase, with GΩ seals. In regions with single channel activity spontaneous synaptic currents could also be recorded, and the channels were threrefore identified as synaptic. The single channel current amplitude was −7 to −8 pA at the resting potential of −70 mV, representing a conductance of 100 pS. The amplitudes decreased by a factor of two when the temperature was lowered by 10°C. Openings occurred in bursts, and the mean burst length varied between 0.3 ms (50 μM glutamate in the pipette) and 0.8 ms (1 mM glutamate in the pipette). After treatment with collagenase, GΩ seals could be formed. The conductance of the channel and the mean burst length was not affected by the enzyme, but after treatment active spots could be found easier and they were distributed more uniformly along the fibre. After treatment the concentrations of glutamate necessary to elicit channel openings were higher (100 μM compared to 20–50 μM) and simultaneous openings of two or more channels were observed very rarely. Synaptic currents could not be recorded from preparations cleaned by collagenase (2 mg/ml) for longer than 60 min.