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- transporters, whose presence in the rat pancreas is still unclear. The Cl-/HCO3- 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 160 kD for AE2, at approximate to 90 kD and approximate to 103 kD for NHE1 and NHE4, respectively, and at 31 kD and 70 kD for V-ATPase. NHE1 and NHE4 were further identified by amplification of isoform-specific cDNA using RT-PCR. Immunohistochemistry revealed a basolateral location of AE2, NHE1, and NHE4 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 immunohistochemistry. The data indicate that NHE1 and NHE4 are co-expressed in rat pancreatic acini and ducts. Basolateral acinar AE2 could contribute to Cl- uptake 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.