AE ANION-EXCHANGER MESSENGER-RNA 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+ concent ration. Among the multiple transport processes that regulate VSMC pH(i ), Na+-independent Cl-/HCO3- exchange is the major process that acidif ies VSMCs in response to an alkaline load. Here, we characterize, in n ative and cultured VSMCs, the expression of the AE family of band S-re lated 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 tes ted. Cultured VSMCs and aorta both expressed a similar to 165-kDa AE(2 ) polypeptide, but a similar to 115-kDa polypeptide was the major AE2- related protein in aorta. AE3 mRNA levels in VSMCs and in arterial tis sue were significantly lower than those for AE2, but AE3 or related po lypeptides were readily detected by immunoblot and immunolocalization experiments. The similar to 125-kDa AE3 polypeptide was present in an immortalized aortic VSMC line, but the predominant AE3 epitope in aort a and most cultured cells was associated with a polypeptide of M-r sim ilar to 80 kDa. These data demonstrate the expression in native arteri es and in VSMCs of products of the AE2 and AE3 genes, which may contri bute to Na+-independent Cl-/HCO3- exchange activity in these tissues a nd cells.