POTENTIATION BY POLYAMINES OF AN INTERACTION OF NONCOMPETITIVE ANTAGONISTS AT THE N-METHYL-D-ASPARTATE RECEPTOR IONOPHORE COMPLEX WITH PHOSPHATIDYLSERINE

The addition of phosphatidylserine induced a significant interaction w ith radioligands widely used for labeling an ion channel associated wi th an N-methyl-D-aspartate (NMDA)-sensitive subclass of brain excitato ry amino acid receptors, such as 0,11-dihydro-5H-dibenzo[a,d]cyclohept en-5,10-imine (MK-801) and [H-3]N-[1-(2-thienyl)cyclohexyl]piperidine, in the absence of brain synaptic membranes irrespective of the additi on of either L-glutamic acid or glycine when determined in the presenc e of the polyamine spermidine. The interaction with [H-3]MK-801 increa sed in proportion to increasing concentrations of phosphatidylserine a dded at concentrations from 0.01 to 0.5 mg/ml. Similar interaction wit h [H-3]MK-801 occurred for phosphatidylinositol to a lesser extent tha n for phosphatidylserine but not for either phosphatidylethanolamine o r phosphatidylcholine at the similar concentration range. The interact ion between phosphatidylserine and [H-3]MK-801 was dependent partially on incubation temperature and on incubation time with reversible and saturable profiles. Among various natural and synthetic polyamines, bo th spermine and bis-(3-aminopropyl)amine in addition to spermidine wer e effective in markedly potentiating the interaction in a concentratio n-dependent manner at concentrations from 1 muM to 10 mM. However, the potentiation by spermidine was insensitive to antagonism by the respe ctive antagonists for the NMDA and glycine domains at 0.1 mM. Moreover , the interaction between phosphatidylserine and [H-3]MK-801 was sensi tive to inhibition by several compounds with an antagonistic activity at calmodulin. The addition of phosphatidylserine completely concealed the potentiation by either glutamate alone or both glutamate and glyc ine of the binding of [H-3]MK-801 in brain synaptic membranes with con comitant enhancement of the ability of spermidine to potentiate the bi nding, while phosphatidylserine failed to affect the affinities of the respective ligands for the NMDA and glycine domains. These results su ggest that the acidic phospholipid phosphatidylserine may at least in part play crucial roles in mechanisms underlying the potentiation by p olyamines of the binding of [H-3]MK-801 to the open NMDA channel in ra t brain.