Desensitization of NMDA receptors depends of their association with plasma membrane sodium-calcium exchangers in lipid nanoclasters

The plasma membrane Na + /Ca 2+ -exchanger (NCX) has recently been shown to regulate Ca 2+ -dependent N -methyl- d -aspartate receptor (NMDAR) desensitization, suggesting tight interaction of NCXs and NMDARs in lipid nanoclaster or “rafts”. To evaluate possible role of this interaction we studied effects of Li + on NMDA-elicited whole-cell currents and Ca 2+ responses of rat cortical neurons in vitro before and after cholesterol extraction by methyl-β-cyclodextrin (MβCD). Substitution Li + for Na + in the external solution caused a concentration-dependent decrease of steady-state NMDAR currents from 440 ± 71 pA to 111 ± 29 pA in 140 mM Na + and 140 mM Li + , respectively. Li + inhibition of NMDAR currents disappeared in the absence of Ca 2+ in the external solution (Ca 2+ -free), suggesting that Li + enhanced Ca 2+ -dependent NMDAR desensitization. Whereas the cholesterol extraction with MβCD induced NMDAR current decrease to 136 ± 32 pA in 140 mM Na + and 46 ± 15 pA in 140 mM Li + , the IC 50 values for the Li + inhibition were similar (about 44 mM Li + ) before and after this procedure. In Ca 2+ -free Na + solution steady-state NMDAR currents after the cholesterol extraction were 47 ± 6 % of control currents. Apparently this amplitude decrease was not Ca 2+ -dependent. In 1 mM Ca 2+ Na + solution the Ca 2+ -dependent NMDAR desensitization was greater when cholesterol was extracted. Obviously, this procedure promoted its development. In agreement, Li + and KB-R7943, an inhibitor of NCX, both considerably reduced NMDAR-mediated Ca 2+ responses. The cholesterol extraction itself caused a decrease of NMDAR-mediated Ca 2+ responses and, in addition, abolished the effects of Li + and KB-R7943. Taken together our data suggest that NCXs downregulate the Ca 2+ -dependent NMDAR desensitization. Most likely, this is determined by co-localization and tight functional interaction of NCX and NMDAR molecules in membrane lipid rafts. Their destruction is accompanied by an enhancement of NMDAR desensitization and a loss of NCX-selective agent effects on NMDARs.