Immunolocalization of anion exchanger AE2, Na+/H+ exchangers NHE1 and NHE4, and vacuolar type H+-ATPase in rat pancreas

We have studied the expression and localization of several H+ and HCO3- tra nsporters, whose presence in the rat pancreas is still unclear. The Cl-/HCO 3- exchanger AE2, the Na+/H+ exchangers NHE1 and NHE4, and the 31-kD and 70 -kD vacuolar H+-ATPase (V-ATPase) subunits were detected by immunoblotting and immunocytochemical techniques. Immunoblotting of plasma membranes with transporter-specific antibodies revealed protein bands at approximate to 16 0 kD for AE2, at approximate to 90 kD and approximate to 103 kD for NHE1 an d NHE4, respectively, and at 31 kD and 70 kD for V-ATPase. NHE1 and NHE4 we re further identified by amplification of isoform-specific cDNA using RT-PC R. Immunohistochemistry revealed a basolateral location of AE2, NHE1, and N HE4 in acinar cells. In ducts, NHE1 and NHE4 were basolaterally located but no AE2 expression was detected. V-ATPase was detected in zymogen granules (ZGs) by immunogold labeling, and basolaterally in duct cells by immunohist ochemistry. The data indicate that NHE1 and NHE4 are co-expressed in rat pa ncreatic acini and ducts. Basolateral acinar AE2 could contribute to Cl- up take and/or pH regulation. V-ATPase may be involved in ZG fusion/exocytosis and ductal HCO3- secretion. The molecular identity of the ductal Cl /HCO3- exchanger remains unclear.