Use-dependent pentobarbital block of kainate and quisqualate currents

Abstract

The effects of pentobarbital on whole-cell excitatory amino acid-induced currents were studies in cultured rat cortical neurons. Currents evoked by 40 μM kainate were reversibly inhibited by pentobarbital with an IC 50 value of 50 μM. The block of the kainate response by pentobarbital was use dependent, requiring kainate stimulation. In the absence of kainate activation, 10 min perfusions of 100 μM pentobarbital inhibited kainate-induced currents less than 10%. Recovery from pentobarbital block also exhibited use dependence, reversing in 5–10 s with kainate stimulation, while persisting 10 min or more in the absence of agonist. Pentobarbital inhibition of the kainate response was not voltage dependent. Responses evoked by 10 μM quisqualate consisted of a peak current desensitizing to a smaller steady-state current. The co-application of 100 μM pentobarbital reduced the steady-state current by49±5%. The peak current before desensitization, however, was inhibited less than 10%. Currents evoked by 25 μM N-methyl- d-aspartate were not significantly inhibited by co-application of 100 μM pentobarbital. The results suggest that the pentobarbital-induced inhibition of kainate responses involves open channel block and that the block of quisqualate currents primarily involve non-desensitizing receptor channels that generate steady-state currents.