Single synaptic channels recorded at glutamate sensitive patches on a crayfish muscle

When a patch clamp pipette filled with 50 mumol/l glutamate was placed on a muscle fiber of the deep abdominal extensor of crayfish, in some locations current pulses were recorded which were identified as synaptic, glutamate-operated ionic channel openings. At a given site all current pulses had approximately the same amplitude. At resting potential and 19 degrees C, their mean amplitudes were 7-8 pA, corresponding to channel conductances of 70-80 pS. The distribution of open times of the channels could be described by the sum of two exponentials with time constants tau 1 of 0.3-0.5 ms for the longer, and tau 2 of 0.03-0.06 ms for the shorter component. Bursts of channel openings interrupted by gaps occurred in about 10% of the events only. The longer time constant tau 1 conforms to the channel open times estimated by noise analysis [11].