title: Casein binds to the cell membrane and induces intracellular calcium signals in the enteroendocrine cell: a brief communication.
abstract: Dietary protein but not amino acids stimulates cholecystokinin (CCK) secretion in rat mucosal cells. However, the dietary protein sensory mechanisms and the intracellular signal pathway in the enteroendocrine cells have not yet been clarified. The relationship between dietary protein binding to cell membrane and intracellular calcium responses were examined in the CCK-producing enteroendocrine cell line STC-1. The binding of solubilized STC-1 cell membrane to proteins was analyzed using a surface plasmon resonance sensor. Intracellular calcium concentrations of STC-1 cell suspensions loaded with Fura-2 AM were measured using a spectrafluorophotometer system with continuous stirring. Intracellular calcium concentrations in STC-1 cells were increased by exposure to alpha-casein or casein sodium, but not to bovine serum albumin. Solubilized STC-1 membranes bound to alpha-casein and casein sodium but did not bind to bovine serum albumin. alpha-Casein demonstrated higher membrane binding and intracellular calcium stimulating activities than casein sodium. Thus, protein binding to the STC-1 cell membrane and intracellular calcium responses were correlated. Intracellular calcium responses to alpha-casein were suppressed by an L-type calcium channel blocker. These results suggest that casein, a dietary protein, binds to a putative receptor on the CCK-producing enteroendocrine cell membrane and elicits the subsequent intracellular calcium response via an L-type calcium channel.
authors.affiliation: Division of Applied Bioscience, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan.
authors.forename: Tohru
authors.initials: T
authors.lastname: Hira
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hara
authors.forename: Fusao
authors.initials: F
authors.lastname: Tomita
authors.forename: Yoritaka
authors.initials: Y
authors.lastname: Aoyama
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002364:Caseins / Q000378:metabolism / Q000494:pharmacology*; D002417:Cattle; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004044:Dietary Proteins / Q000378:metabolism / Q000494:pharmacology*; D019858:Enteroendocrine Cells / Q000187:drug effects / Q000378:metabolism*; D016257:Fura-2 / Q000737:chemistry; D007424:Intracellular Fluid / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000378:metabolism / Q000494:pharmacology; D013050:Spectrometry, Fluorescence; D020349:Surface Plasmon Resonance
chemical_list: D002121:Calcium Channel Blockers; D002364:Caseins; D004044:Dietary Proteins; D012710:Serum Albumin, Bovine; D002118:Calcium; D016257:Fura-2