Calcium regulation of gene expression is critical for the long-lasting activity-dependent changes in cellular electrical properties that underlie important physiological functions such as learning and memory. Cellular electrical properties are diversified through the extensive alternative splicing of ion channel pre-messenger RNAs; however, the regulation of splicing by cell signalling pathways has not been well explored. Here we show that depolarization of GH3 pituitary cells represses splicing of the STREX exon in BK potassium channel transcripts through the action of Ca2+/calmodulin-dependent protein kinases (CaMKs). Overexpressing constitutively active CaMK IV, but not CaMK I or II, specifically decreases STREX inclusion in the mRNA. This decrease is prevented by mutations in particular RNA repressor sequences. Transferring 54 nucleotides from the 3' splice site upstream of STREX to a heterologous gene is sufficient to confer CaMK IV repression on an otherwise constitutive exon. These experiments define a CaMK IV-responsive RNA element (CaRRE), which mediates the alternative splicing of ion channel pre-mRNAs. The CaRRE presents a unique molecular target for inducing long-term adaptive changes in cellular electrical properties. It also provides a model system for dissecting the effect of signal transduction pathways on alternative splicing.