Amperometric monitoring of chemical secretions from individual pancreatic beta-cells.

The goal of the work was to develop and test an amperometric method for measuring insulin secretion from individual pancreatic beta-cells. The electrode used was a carbon fiber microelectrode modified with a polynuclear ruthenium oxide/cyanoruthenate film. The chemically modified electrode allowed anodic detection of insulin in physiological buffers with a detection limit of 0.5 microM. To measure secretion, an electrode was positioned 1 micron away from a beta-cell that had been stimulated with K+ or glucose. Recordings made from the cells consisted of a series of current spikes averaging 38 ms full width at half-height. The spikes decreased in height and increased in width as the electrode was pulled away from the cell. Spikes were only observed if a modified electrode was used and its potential was sufficient to oxidize insulin. The area under the spikes correspond to approximately 600 zmol of insulin, which is within the expected range for vesicular insulin content. Spike area was independent of stimulation method. The results support the hypothesis that the electrode was anodically detecting a substance secreted from the cells by exocytosis. The results support, but do not prove, that insulin was the primary substance detected.