title: Depolarization-independent net uptake of calcium into clonal insulin-releasing cells exposed to glucose.
abstract: Insulin release, net fluxes of Ca2+, and glucose metabolism were studied in a clonal cell line (RINm5F) established from a transplantable rat islet tumor. The insulin content amounted to only 0.03% of that of the total protein and decreased even further with subsequent passages. The insulin secretion was as high as 10 to 20% of the total hormone content per hour. Insulin release was stimulated by K+ depolarization but not by exposure to glucose. In contrast to this secretory pattern, glucose but not K+ stimulated the net uptake of Ca2+ at micromolar concentrations of the ion. The glucose effect was not mimicked by 20 mM 3-O-methylglucose. It was as pronounced at 1 mM as at 20 mM of the sugar and corresponded to an uptake of 119 fmol cm-2 s-1. Glucose metabolism was typical for tumor cells with a high glycolytic flux and an oxidation-to-utilization ratio as low as 0.05-0.15. Maximal oxidative degradation was attained already at 1 mM. This concentration was also equivalent to the Km for glucose utilization, indicating a substantial left-hand shift of the normal dose-response curve. It is suggested that glucose induces a depolarization-independent net uptake of Ca2+ by favouring intracellular buffering of the cation.
mesh_terms: D007516:Adenoma, Islet Cell / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism*; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology*; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D010190:Pancreatic Neoplasms / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats
chemical_list: D007328:Insulin; D005947:Glucose; D011188:Potassium; D002118:Calcium