Enzymatic Studies of Glucose Phosphorylation in the Glucagon-Producing Cells of Duck Pancreas

Abstract

The glucagon-producing A₂-cells of the pancreatic islets seem to show a reversed secretory response to glucose in comparison with the insulin-producing B-cells. In this investigation, the glucose phosphorylating process has been studied in A₂-cells isolated from cryostat sections of duck pancreases. The cell samples were prepared by free-hand dissection in cold heptane during observation with a dark field stereo microscope. Measurements of the hexokinase activity at high and low glucose concentrations indicated a low phosphorylating capacity of the A₂-cells. Hexokinase activity was about 0.15 MKH (moles substrate converted per kg dry weight per hour of incubation). K_m was between 3 × 10^-5 and 4 × 10^-5M. Comparisons of nexokinase activity were made with pancreatic acini, liver and heart muscle. No high-K_m hexokinase was found in the A₂-cells, while the presence of glucokinase was easily demonstrated in the liver. These results strongly suggest that the phosphorylation of glucose in the A₂-cells is of lower regulatory importance than in the B-cells. 1 Supported by the Swedish Medical Research Council (Project No. B71-12X-525-07C), the Medical Faculty of Uppsala, The Swedish Diabetes Association and the Åhlén Foundation.