In this study, the prevalence and identity of the cells expressing functional receptors for the gastrointestinal (GI) peptide hormones: gastrin, bombesin, and neurotensin in dissociated cells from 20 freshly resected human primary colorectal carcinomas were determined.GI peptide hormone-induced increases in the concentration of free intracellular Ca(2+) ([Ca(2+)](i)) were used as an assay for the detection of functional receptors. Reverse-transcription polymerase chain reaction (RT-PCR) was performed in a subset of tumor samples. Agonist-responsive cells were identified as either of epithelial or stromal origin by immunocytochemistry with cytokeratin and vimentin antibodies, respectively.Overall, expression of GI peptide hormone receptors was more frequent in stromal cells when compared to epithelial cells. Of the three receptors, expression of bombesin receptor (95%) was most prevalent in vimentin-positive (stromal) cells; whereas, gastrin receptor expression by cytokeratin-positive (epithelial) cells was more common (39%). A single gastrin receptor splice variant differentially regulates [Ca(2+)](i) in a cell-type specific manner. The gastrin receptor-expression profile in the 11 colon cancer-derived cell lines did not reflect the prevalence of expression in primary human cancers.The Ca(2+) assay is a sensitive method for detecting functional GI peptide hormone receptor expression by colon cancer cells. Because this approach utilizes living cells, it is amenable to further functional analyses of signal transduction mechanisms at the single cell level. Importantly, our data provide a rationale for examining of the role of these GI peptide hormones and their cognate receptors in mesenchymal cell biology.