Gastrin plays a crucial role in maintaining a normal cellular composition and function of the oxyntic mucosa. It has been debated for decades whether parietal cells possess cholecystokinin-2 (CCK2) receptors and interact directly with gastrin. We investigated whether parietal cells express CCK2 receptor mRNA by using new molecular biology techniques. Rat oxyntic mucosal cells were dispersed and enriched by elutriation, and single parietal and ECL cells were isolated from cell smears by means of laser microbeam microdissection and laser pressure catapulting. The mRNA from each single cell was isolated and subjected to one-step multiplex or conventional reverse transcription-polymerase chain reaction and subsequent nested PCR. Specific primers for the CCK2 receptor were used in combination with primers for H,K-ATPase and histidine decarboxylase, specific markers for parietal and ECL cells, respectively. CCK2 receptor mRNA was detected in 25% of the rat parietal cells and 40% of the ECL cells examined. (C) 2002 Published by Elsevier Science (USA).