AE anion exchanger mRNA and protein expression in vascular smooth muscle cells, aorta, and renal microvessels

Intracellular pH (pH(i)) is an important regulator of vascular smooth muscle cell (VSMC) tone, contractility, and intracellular Ca²⁺ concentration. Among the multiple transport processes that regulate VSMC phi, Na⁺-independent Cl^-/HCO₃/^exchange is the major process that acidities VSMCs in response to an alkaline load. Here, we characterize, in native and cultured VSMCs, the expression of the AE family of band 3-related anion exchangers, the best studied of these Cl^-/HCO₃/^- exchangers. A 4.2-kb AE2 mRNA was present in aorta and in all cultured VSMCs tested. Cultured VSMCs and aorta both expressed a ~165-kDaAE2 polypeptide, but a ~115-kDa polypeptide was the major AE2-related protein in aorta. AE3 mRNA levels in VSMCs and in arterial tissue were significantly lower than those for AE2, but AE3 or related polypeptides were readily detected by immunoblot and immunolocalization experiments. The ~125-kDa AE3 polypeptide was present in an immortalized aortic VSMC line, but the predominant AE3 epitope in aorta and most cultured cells was associated with a polypeptide of Mr ~80 kDa. These data demonstrate the expression in native arteries and in VSMCs of products of the AE2 and AE3 genes, which may contribute to Na⁺-independent Cl^-/HCO₃/^- exchange activity in these tissues and cells.