ENHANCED TYROSINE PHOSPHORYLATION OF THE 2B SUBUNIT OF THE N-METHYL-D-ASPARTATE RECEPTOR IN LONG-TERM POTENTIATION

Both serine/threonine and tyrosine phosphorylation of receptor protein s have been implicated in the process of long-term potentiation (LTP), but there has been no direct demonstration of a change in receptor ph osphorylation after LTP induction, we shelf that, after induction of L TP in the dentate gyrus of anesthetized adult rats, there is an increa se in the tyrosine phosphorylation of the 2B subunit of the N-methyl-D -aspartate (NMDA) receptor (NR2B), as well as several other unidentifi ed proteins. Tyrosine phosphorylation of NR2B was measured in two ways : binding of antiphosphotyrosine antibodies (PY20) to glycoprotein(s) of 180 kDa (GP180) purified on Con A-Sepharose and binding of anti-NR2 B antibodies to tyrosine-phosphorylated proteins purified on PY20-agar ose. Three hours after LTP induction, anti-NR2B binding to tyrosine ph osphorylated proteins, expressed as a ratio of tetanized to control de ntate (Tet/Con), was 2.21 +/- 0.50 and PY20 binding to GP180 was 1.68 +/- 0.16. This increase in the number of tyrosine phosphorylated NR2B subunits occurred without a change in the total number of NR2B subunit s. When the induction of LTP was blocked by pretreatment of the animal with the NMDA receptor antagonist MK801, the increase in PY20 binding to GP180 was also blocked (Tet/Con = 1.09 +/- 0.26). The increased PY 20 binding to GP180 was also apparent 15 min after LTP induction (Tet/ Con = 1.41 +/- 0.16) but not detectable 5 min after LTP induction (Tet /Con = 1.01 +/- 0.19). These results suggest that tyrosine phosphoryla tion of the NMDA receptor contributes to the maintenance of LTP.