Multiple functional P2X and P2Y receptors in the luminal and basolateral membranes of pancreatic duct cells

Purinergic receptors in the basolateral and luminal membranes ofthe pancreatic duct can act by a feedback mechanism to coordinate transport activity in the two membranes during ductal secretion. Thegoal of the present work was to identify and localize the functional P2receptors (P2R) in the rat pancreatic duct. The lack of selectiveagonists and/or antagonists for any of the cloned P2R dictated the useof molecular and functional approaches to the characterization ofductal P2R. For the molecular studies, RNA was prepared frommicrodissected pancreatic intralobular ducts and was shown to be freeof mRNA for amylase and endothelial nitric oxide synthase (markers foracinar and endothelial cells, respectively). A new procedure isdescribed to obtain an enriched preparation of single duct cellssuitable for electrophysiological studies. Localization of P2R wasachieved by testing the effect of various P2R agonists on intracellularCa²⁺ concentration([Ca²⁺]_i)of microperfused intralobular ducts. RT-PCR analysis suggested theexpression of six subtypes of P2R in the pancreatic duct: three P2YRand three P2XR. Activation ofCl current by variousnucleotides and coupling of the receptors activated by thesenucleotides to G proteins confirmed the expression of multiple P2R induct cells. Measurement of[Ca²⁺]_iin microperfused intralobular ducts suggested the expression ofP2X₁R,P2X₄R, probablyP2X₇R, and as yet unidentifiedP2YR, possibly P2Y₁R, in thebasolateral membrane. Expression ofP2Y₂R, P2Y₄R, andP2X₇R was found in the luminalmembrane. The unprecedented expression of such a variety of P2R in onecell type, many capable of activatingCl channels, suggests thatthese receptors may have an important role in pancreatic duct cell function.