Figure 1. Possible multiple protein interactions controlling HCO3 - secretion in pancreatic ducts. Several membrane receptors and transporters participating in HCO3 - homeostasis in pancreatic duct cells have a PDZbinding motif (-X-T/S-X-hydrophobic amino acid) on their C-terminus. The C-terminal sequences are based on the human clones. Except for several purinergic receptors, most of the proteins are associated with cAMP-dependent processes. The abbreviations used are: DRA, down-regulated in adenoma; NBC, Na+-HCO3 - co-transporter; P2, purinergic receptor; RII, regulatory subunit of protein kinase A type II.