Polyamines are also important modulators of a variety of ion channels , including NMDA receptors and AMPA receptors . They block inward-rectifier potassium channels so that the currents of the channels are inwardly rectified, thereby the cellular energy, . K +
ion gradient across the cell membrane, is conserved. In addition, polyamine participate in initiating the expression of SOS response of Colicin E7 operon and down-regulate proteins that are essential for colicin E7 uptake, thus conferring a survival advantage on colicin-producing E. coli under stress conditions.