Release and characterization of cholecystokinin from isolated canine jejunal cells

Abstract

We have developed an isolated intestinal cell system to study the regulation of cholecystokinin release. Enzymatically dispersed canine jejunal mucosal cells were separated by counterflow elutriation to enrich cholecystokinin content 20-fold. Release of cholecystokinin from freshly isolated cells was determined by radioimmunoassay. Elevated extracellular potassium, dibutyryl cyclic adenosine monophosphate, and the diterpene derivative forskolin each stimulated an increase in cholecystokinin release over a 60-min period compared to basal secretion. l-Tryptophan stimulated a dose-dependent and stereospecific increase in cholecystokinin. d-Tryptophan did not significantly alter basal cholecystokinin secretion. Carbachol inhibited l-tryptophan-stimulated cholecystokinin release in a dose-dependent manner. Analysis of extracts from intact jejunal mucosa by high-pressure liquid chromatography revealed three components with cholecystokinin immunoreactivity eluting in positions with cholecystokinin 8, with cholecystokinin 33/39, and after cholecystokinin 33/39. Only the two molecular forms coeluting, respectively, with cholecystokinin 8 and cholecystokinin 33/39 were present in the elutriator-enriched jejunal cells, and these two forms of cholecystokinin immunoreactivity were released from cells upon stimulation. These data suggest (a) that l-tryptophan directly regulates the release of cholecystokinin and (b) that membrane depolarization and intracellular generation of cyclic adenosine monophosphate may play a role in activating cholecystokinin cells. Stimulated cholecystokinin release is inhibited by the muscarinic agonist carbachol. The molecular profile of released cholecystokinin corresponded to the two molecular components, cholecystokinin 8 and cholecystokinin 33/39, contained in dispersed cells.