Summary
Excitatory postsynaptic currents (EPSCs) were measured as clamp current of muscle fibers or by focal extracellular recording. In the control bathing solution the voltage dependence of the EPSC was nearly linear in the potential range between −160 to −40 mV, in most experiments the slope of this relation decreased at potentials more negative than the resting potential. In 5×Ca++ solution at potentials more negative than −70 to −100 mV the slope of the current voltage relation of the EPSC was zero or negative. The reversal potentials for the EPSCs, extrapolated from the current voltage relation, were at +33 mV (S.D.±32 mV) both in 1×Ca++ and in 5×Ca++ solution.
The declining phase of EPSCs was slowed by depolarization and shortened by hyperpolarization, its time constant increasing by about 100% between −160 mV and −40 mV.
Excitatory postsynaptic currents also were elicited by glutamate-pulses (g-EPSCs). In 1×Ca++ and in 5×Ca++ solutions the amplitude of the g-EPSCs showed a voltage dependence like that of the EPSCs. In 10×Ca++ solution (10% normal Na+) synaptic current was reduced to about 50%. The current voltage relation was very flat and showed a negative slope for high negative potentials.
It is concluded that Na+-, Ca++- and K+-ions contribute to the EPSC. Synaptic sodium and/or calcium conductance seems to decrease at potentials more negative than the resting potential.
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This investigation was supported by a grant of the Deutsche Forschungsgemeinschaft (Du 24/14).
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Dudel, J. Nonlinear voltage dependence of excitatory synaptic current in crayfish muscle. Pflugers Arch. 352, 227–241 (1974). https://doi.org/10.1007/BF00590488
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DOI: https://doi.org/10.1007/BF00590488