Effects of polyamines on NMDA-induced currents in rat hippocampal neurons: a whole-cell and single-channel study.
Actions of the polyamines spermine and spermidine on NMDA-induced currents were examined in cultured hippocampal neurons from embryonic rat. In whole-cell patch experiments using voltage-clamp, spermine (300 microM) produced about a two-fold potentiation of responses to NMDA (at -70 mV in the presence of saturating glycine); half-maximal potentiation was elicited at 207 microM. The potentiation produced by spermine was somewhat greater at positive potentials. The onset of potentiation was fast (t1/2 < 1 s), indicative of an extracellular site of action. Spermidine was of comparable potency but less efficacious than spermine in potentiating NMDA responses. In excised outside-out patches, spermine exhibited two actions on NMDA-induced single-channel responses. In some patches, it increased the channel open probability; both frequency of channel opening and burst length were increased with no significant change in the mean open duration, which accounted for much of the potentiation seen in whole-cell experiments. In all patches, spermine decreased channel conductance at negative voltages, an effect ascribable to fast channel block (with a possible contribution by charge screening). These results are consistent with opposing actions of polyamines mediated at distinct sites on the NMDA receptor.
Araneda
R C
RC
Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461.
Zukin
R S
RS
Bennett
M V
MV
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002478:Cells, Cultured; D004357:Drug Synergism; D006624:Hippocampus / Q000187:drug effects*; D015640:Ion Channel Gating / Q000187:drug effects; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D013095:Spermidine / Q000494:pharmacology*; D013096:Spermine / Q000494:pharmacology*
D013096:Spermine; D016202:N-Methylaspartate; D013095:Spermidine