TISSUE-SPECIFICITY AND ALTERNATIVE SPLICING OF THE NA+ CA2+ EXCHANGERISOFORMS NCX1, NCX2, AND NCX3 IN RAT/

The gene coding for the Na+/Ca2+ exchanger NCX1 is characterized by a cluster of six exons (A, B, C, D, E, and F) coding for a variable regi on in the COOH terminus of the large intracellular loop of the protein . Alternative splicing of these exons generates multiple tissue-specif ic variants of NCX1. Using reverse transcriptase-polymerase chain reac tion, we analyzed eight previously described and four new splicing iso forms of NCX1 in a wide variety of tissues and cells. Exons A and B ar e mutually exclusive, as shown in earlier studies, and splicing isofor ms containing exon A are preferentially expressed in heart, brain, and skeletal muscle, whereas splicing variants with exon B are found in a ll rat tissues except heart. The second and third isoforms of the Na+/ Ca2+ exchanger, NCX2 and NCX3, show a deletion of 37 amino acids in th e intracellular loop corresponding to parts of the variable region of NCX1. We identified three splicing isoforms of NCX3 in brain and skele tal muscle by reverse transcriptase-polymerase chain reaction. These s plice variants are generated by including either of two alternative ex ons equivalent to the NCX1 exon A or B and by including or excluding a sequence equivalent to the NCX1 exon C. We did not detect any alterna tive splicing of NCX2. We examined selected tissues from neonatal and adult rats and found developmental regulation for NCX1 and NCX3 splici ng isoforms in skeletal muscle. Specific isoform patterns were also de tected for NCX1 and NCX3 in cultured cortical neurons, astrocytes, and oligodendrocytes. We suggest a new terminology to distinguish the dif ferent splice variants of individual NCX isoforms.