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Modulation of cellular differentiation by N‐methyl‐d‐aspartate receptors in osteoblasts

N‐Methyl‐d‐aspartate (NMDA) receptors for the central neurotransmitter l‐glutamate (Glu) have been shown to be present in both osteoblasts and osteoclasts. Sustained exposure to the NMDA channel antagonist dizocilpine (MK‐801) significantly prevented increases in both alkaline phosphatase activity and Ca2+ accumulation in a concentration‐dependent manner in osteoblasts cultured for 7–28 days in vitro (DIV), without significantly affecting cell survivability. Osteocalcin expression was markedly reduced in the presence of MK‐801 in osteoblasts cultured for 28 DIV. Both an NMDA domain antagonist and a glycine domain antagonist similarly prevented Ca2+ accumulation in osteoblasts exposed for 28 consecutive DIV. MK‐801 was effective in significantly inhibiting Ca2+ accumulation determined at 28 DIV in osteoblasts exposed before 7 DIV but was ineffective in cells exposed after 11–21 DIV. Sustained exposure to MK‐801 significantly inhibited DNA binding activity and expression of core binding factor α‐1 (CBFA1) in osteoblasts exposed after 7 DIV up to 28 DIV, but not in those exposed before 7 DIV. These results suggest that heteromeric NMDA receptor channels may be functionally expressed to regulate mechanisms underlying cellular differentiation rather than proliferation and/or maturation through modulation of expression of CBFA1 in cultured rat calvarial osteoblasts.