Permeability changes produced by L-glutamate at the excitatory post-synaptic membrane of the crayfish muscle.
1. Permeability changes produced by L-glutamate at the neuromuscular junction of the crayfish (Cambarus clarkii) were investigated by application of the drug iontophoretically to the voltage-clamped junction and measuring the resulting 'glutamate current'. 2. Reversal potentials were determined by measuring the glutamate current at different membrane potentials. They were +39-1 +/- 3-6 mV (mean +/- S.E. of mean) in normal solution and +16-5 +/- 2-0 mV in solutions made twice as hypertonic by the addition of sucrose. 3. Decreasing external Na+ concentration shifted the reversal potential in the negative direction; increased Na+ in the positive direction. 4. The relation between the amplitude of the glutamate current and extracellular Na+ concentration was approximately linear. 5. Alteration of the external K+ or Cl- concentration did not affect the amplitude or reversal potential of glutamate current. 6. In Na+-free solution the application of L-glutamate produced a small inward current at the resting potential and its amplitude was augmented by increasing the external Ca2+ concentration. 7. Increasing the Ca2+ concentration in the normal Na+ media produced no appreciable effect on the reversal potential but decreased the amplitude of glutamate current. 8. The results indicate that L-glutamate increases the membrane permeability mainly to Na+ and slightly to Ca2+. 9. The time course of glutamate current was shorter than that of the concentration calculated from the diffusion equation and it was simulated more closely by the square of the concentration.
D000818:Animals; D003400:Astacoidea; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects*; D002712:Chlorides / Q000494:pharmacology; D005971:Glutamates / Q000494:pharmacology*; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology / Q000502:physiology; D013570:Synaptic Membranes / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
D002712:Chlorides; D005971:Glutamates; D012964:Sodium; D011188:Potassium; D002118:Calcium