Modulation and block of ion channels: a new biology of polyamines.

The endogenous polyamines, spermine, spermidine, and putrescine have effects on several types of cation channels. Intracellular polyamines, in particular spermine, contribute to intrinsic gating and rectification of strong inward rectifier K+ channels. Intracellular spermine is also responsible for inward rectification of some types of Ca(2+)-permeable AMPA and kainate receptors. Spermine has a number of effects on the activity of the NMDA subtype of glutamate receptor, involving two or more extracellular polyamine binding sites on the NMDA receptor. In K+ channels and glutamate receptors, some of the amino acids in the receptor/channel structure that influence to polyamines have been identified, leading to a partial understanding of the effects of polyamines at a molecular level. Block of K+ channels by intracellular polyamines is likely to be an important receptors by intracellular spermine and modulation by extracellular spermine may affect excitability and the influx of Ca2+ in neurons and glial cells of the nervous system.