On the mechanism of desensitization in quisqualate-type glutamate channels

Desensitization of crayfish glutamate channels was studied in outside-out p atches employing an improved fast drug-application technique. Low concentra tions of glutamate produced substantial desensitization without correlation with the detected number of open channels. The desensitization time consta nt (tau(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 occu rs also from channels in a partly-liganded state. A kinetic model was devel oped. The model accounts for the multifaceted behavior of desensitization a s well as for resensitization.