NA/CA EXCHANGER ISOFORMS EXPRESSED IN KIDNEY

The cardiac (versus retinal rod) Na/Ca exchanger gene has been cloned, sequenced and shown by RNA analysis to be present in diverse tissues. Analysis of published sequences shows that a single isoform is found in heart tissue from many species (NACA1 isoform). We provide evidence here by ribonuclease (RNase) protection assays and by reverse transcriptase-polymerase chain reaction (PCR) amplification with sequence analysis that a new isoform encoding the Na/Ca exchanger is present in renal tissue. This isoform (NACA3) reveals a 7-amino acid deletion in the tested region compared with the NACA2 isoform described by Reilly and Shugrue [Am. J. Physiol. 262 (Renal Fluid Electrolyte Physiol. 31): F1105-F1109, 1992] and is the dominant exchanger transcript in kidney. Analysis of the sequence of all isoforms indicates that the differences in the isoforms reside in the large intracellular loop region of the protein. Alternative splicing of a single Na/Ca exchanger message may be responsible for these tissue-specific transcripts.