A spliced variant of AE1 gene encodes a truncated form of Band 3 in heart:the predominant anion exchanger in ventricular myocytes

The anion exchangers (AE) are encoded by a multigenic family that comprises at least three genes, AE1, AE2 and AE3, and numerous splicoforms. Besides regulating intracellular pH (pH(i)) via the Cl-/HCO3- exchange, the AEs exe rt various cellular functions including generation of a senescent antigen, anchorage of the cytoskeleton to the membrane and regulation of metabolism. Most cells express several AE isoforms, Despite the key role of this famil y df proteins, little is known about the function of specific AE isoforms i n any tissue, including the heart, We therefore chose isolated cardiac cell s, in which a tight control of pHi is mandatory for the excitation-contract ion coupling process, to thoroughly investigate the expression of the AE ge nes at both the mRNA and protein levels, RT-PCR revealed the presence of AE 1, AE2 and AE3 mRNAs in both neonatal and adult rat cardiomyocytes, AE1 is expressed both as the erythroid form (Band 3 or eAE1) and a novel alternate transcript (nAE1), which was more specifically characterized using a PCR m apping strategy. Two variants of AE2 (AE2a and AE2c) were found at the mRNA level. Cardiac as well as brain AE3 mRNAs were expressed in both neonatal and adult rat cardiomyocytes. Several AE protein isoforms were found, inclu ding a truncated form of AE1 and two AE3s, but there was no evidence of AE2 protein in adult rat cardiomyocytes. In cardiomyocytes transfected with an AE3 oligodeoxynucleotide antisense, AE3 immunoreactivity was dramatically decreased but the activity of the Cl-/HCO3- exchange was unchanged. In cont rast, intracellular microinjection of blocking anti-AE1 antibodies inhibite d the AE activity. Altogether, our findings suggest that a specific and nov el AE1 splicoform (nAE1) mediates the cardiac Cl-/HCO3- exchange. The multi ple gene and protein expression within the same cell type suggest numerous functions for this protein family.