In vitro study of cultured human insulinoma cells: evidence of abnormal sensitivity to glucose.

Human insulinoma cells were isolated and cultured in vitro, and their functional and morphological characteristics were determined. The cells, isolated as single cells or small cell clusters, reaggregated to almost the size of islets by the fifth culture day and were maintained in vitro for more than 1 month. Morphologically (light and electron microscopies) they were intact throughout the culture period. Immunohistochemically more than 50% of the cells in each reaggregate contained insulin. Incubation experiments revealed that a low glucose concentration (15 mg/dL) was sufficient to produce maximal insulin release. In the absence of glucose, 1 microgram/mL glibenclamide increased insulin release. On the other hand, 5 mM theophylline and 10 mM arginine did not alter insulin release significantly. Theophylline, arginine, and glibenclamide did not have any stimulatory effect on insulin release in the presence of 50 mg/dL glucose. Perifusion experiments with 50 mg/dL glucose disclosed a biphasic pattern of insulin release, and no significant change in insulin release occurred when the glucose concentration in the perifusate was switched from 50 to 150 and then back to 50 mg/dL. These findings demonstrate that human insulinoma cells can be isolated and maintained in vitro and that the cells have abnormal sensitivity to glucose.