Glutamate-operated postsynaptic channels and spontaneous excitatory postsynaptic currents in crayfish claw opener muscle.

In opener muscle fibres of the crayfish claw excitatory postsynaptic currents activated by glutamate (1 . 10(-4)-5 . 10(-4) mol/l) were investigated by means of the noise analysis technique. For the apparent mean open time of glutamate-activated channels, tau noise = 1.15 ms +/- 0.16 (S.D., n = 24) resulted at membrane potentials between E = -60 mV and E = -100 mV, T = 20-23 degrees C. No significant voltage dependence for tau noise was observed, most likely due to the pretreatment of the fibres with 1 mumol/l concanavalin A. For the conductance, gamma, of these channels, gamma = 23.6 pS +/- 5.2 (S.D., n = 24) was found. These characteristics for glutamate-operated channels differ significantly from those observed recently in opener muscle fibres of crayfish first walking leg [13]. Similarly, different characteristics were found also for the decay time constants tau (sEPSCs) of spontaneous excitatory postsynaptic currents in the respective muscles. On average, tau (sEPSCs) was 1.3 ms +/- 0.3 (S.D., n = 11) in the claw. In the first walking leg tau (sEPSCs) was shorter by a factor of about 2.4 and in the second walking leg shorter by a factor of about 2.9, than in the claw.