Transient expression of NMDA receptor subunit NR2B in the developing rat heart

NMDA receptors represent a subtype of the ionotropic glutamate receptor fam ily, comprising three classes of subunits (NR1, NR2A-D, NR3), which exhibit distinct patterns of regional and developmental expression in the CNS. Rec ently, some NMDA receptor subunits have also been described in adult extran euronal tissues and keratinocytes. However, their developmental expression patterns are currently unknown. With use of RT-PCR and western blot analysi s, the expression of NMDA receptor subunit NR2B was investigated in the dev eloping rat heart. NR2B mRNA and protein were detected in heart tissue of r ats from embryonic day 14 until postnatal day 21 but disappeared 10 weeks a fter birth. in contrast, no NMDA receptor subunit NR1, alpha -amino-3-hydro xy-5-methylisoxazole-4-propionic acid receptor subunit GluR2, or anchoring postsynaptic density protein-95 could be detected in rat heart at any devel opmental stage. Confocal microscopy of cultured cardiac myocytes (CMs) from neonatal rats revealed distinct NR2B staining mainly of intracellular stru ctures. However, no functional NMDA receptor could be detected on CMs by wh ole-cell recordings. In conclusion, high concentrations of NR2B protein can be detected in early rat heart development, but its function still remains elusive.