Ca²⁺ and pH modulate alternative splicing of exon 5 in NMDA receptor subunit 1

RT-PCR and intracellular Ca²⁺ measurements were used to identify factors that modulate alternative splicing of exon 5 in the NMDA receptor transcript encoding NR1, in cultured cerebellar granule neurons. Although cells grown in media containing 5 mM KCl demonstrate compromised survival they show the predicted developmental transition from NR1a (-exon 5) to NR1b (+exon 5) mRNA expression. This transition was blocked under culture conditions that promote survival; inclusion or exclusion of exon 5 is a reversible process that is sensitive to alterations in Ca²⁺ and pH. We conclude that alternative splicing of NR1 pre-mRNA transcripts may be regulated by developmental cues that modulate the degree of glutamate receptor activation.