INTRACELLULAR SPERMINE CONFERS RECTIFICATION ON RAT CALCIUM-PERMEABLEAMPA AND KAINATE RECEPTORS

1. Whole-cell recordings were made from cerebellar granule cells cultu red in high-K+ medium to induce expression of Ca2+-permeable AMPA rece ptors. Current-voltage (I-V) plots of agonist-evoked responses showed varying degrees of inward rectification, but became linear within 5-10 min. 2. Recombinant Ca2+-permeable kainate receptors, composed of Glu R6(Q)/KA-2 subunits, exhibited rectifying whole-cell I-V plots that be came linear in outside-out patches. 3. Loss of rectification in granul e cells was prevented by including 100 mu M spermine in the pipette; t he degree of rectification was then correlated with Ca2+ permeability. 4. Spermine also prevented loss of rectification in patches containin g GluR6(Q)/KA-2 receptors (IC50, 1.7 mu M). 5. We suggest that spermin e, or a similar cellular constituent, may act as a cytoplasmic factor conferring inward rectification on Ca2+-permeable non-NMDA receptors, and that 'washout' of this factor underlies the observed loss of recti fication.