INTRACELLULAR SPERMINE CONFERS RECTIFICATION ON RAT CALCIUM-PERMEABLE AMPA AND KAINATE RECEPTORS

1. Whole-cell recordings were made from cerebellar granule cells cultured in high-K+ medium to induce expression of Ca2+-permeable AMPA receptors. 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 GluR6(Q)/KA-2 subunits, exhibited rectifying whole-cell I-V plots that became linear in outside-out patches. 3. Loss of rectification in granule cells was prevented by including 100 mu M spermine in the pipette; the degree of rectification was then correlated with Ca2+ permeability. 4. Spermine also prevented loss of rectification in patches containing GluR6(Q)/KA-2 receptors (IC50, 1.7 mu M). 5. We suggest that spermine, 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 rectification.