On the mechanism of desensitization in quisqualate-type glutamate channels

Desensitization of crayfish glutamate channels was studied in outside- out patches employing an improved fast drug-application technique. Low concentrations of glutamate produced substantial desensitization without correlation with the detected number of open channels. The desensitization time constant (τ(D)) was found to be independent of glutamate concentration (0.3-20 mM). These results suggest that in addition to desensitization from a state of fully liganded channels, a substantial fraction of desensitization occurs also from channels in a partly-liganded state. A kinetic model was developed. The model accounts for the multifaceted behavior of desensitization as well as for resensitization.