Blockade of ionotropic quisqualate receptor desensitization by wheat germ agglutinin in cultured postnatal rat hippocampal neurons.
1. The effects of the lectin wheat germ agglutinin (WGA) on quisqualate-gated currents were examined in postnatal rat hippocampal neurons using recordings from whole cells and outside-out membrane patches. 2. Rapid applications of quisqualate to whole cells and outside-out patches evoked a current that desensitized to a steady-state level. WGA blocked desensitization by increasing the steady-state current amplitude without altering the current-voltage (I-V) relationship or pharmacology of the current. 3. In outside-out patches quisqualate (2.5-1,000 microM) elicited bursts of channel openings having conductances of 2.7, 6.3, and 13 pS. The mean burst length for all conductances was 8.6 +/- 0.6 ms (mean +/- SE) and exhibited little voltage (-110 to +80 mV) or concentration (2.5-1,000 microM) dependence. Treating patches with 580 nM WGA produced no change in conductance, but the mean burst length for 100 microM quisqualate increased from 9.0 +/- 1.1 to 16 +/- 3.2 ms. 4. Fluctuation analysis of whole cell currents evoked by 1 microM quisqualate at -80 mV revealed an increase in the time constant from 8.7 +/- 0.5 to 13 +/- 1.0 ms after treatment with 580 nM WGA. This treatment produced no change in the estimated single-channel conductance. 5. These findings suggest that an increase in channel burst length, rather than an increase in single-channel conductance, contributes to the WGA-induced augmentation of the steady-state quisqualate current.
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D004594:Electrophysiology; D018691:Excitatory Amino Acid Antagonists; D006624:Hippocampus / Q000166:cytology / Q000187:drug effects*; D015640:Ion Channel Gating / Q000187:drug effects; D007473:Ion Channels / Q000187:drug effects; D009474:Neurons / Q000187:drug effects*; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018091:Receptors, AMPA; D014909:Wheat Germ Agglutinins / Q000494:pharmacology*
D018691:Excitatory Amino Acid Antagonists; D007473:Ion Channels; D018091:Receptors, AMPA; D014909:Wheat Germ Agglutinins; D016318:Quisqualic Acid