O2 consumption by isolated pancreatic islets, as measured in a microincubation system with a Clark-type electrode

The role of B-cell respiration in fuel-induced insulin secretion has not been clarified. Therefore, a new method for the measurement of O2 uptake in islets of Langerhans was developed. An all-glass microincubation chamber was equipped with a Clark-type electrode, a stirring bar, and a special channel for loading the chamber with islets, media, and test compounds. The sensitivity of the system was sufficient for convenient determination of O2 consumption by less than 100 islets. Using DNA as reference value, the exactness of the method was scaled up considerably. Basal O2 uptake in mouse islets amounted to 5.6 +/- 0.2 nmol/h/micrograms DNA. alpha-Ketoisocaproic acid (2.5-20 mM) enhanced O2 consumption by 63-207%. The rate of O2 uptake as well as those of insulin secretion and oxidation of alpha-ketoisocaproic acid in incubated mouse islets were maximal at about 10 mM alpha-ketoisocaproic acid. 14CO2 production from U-14C-labeled alpha-ketoisocaproic acid was up to 36% lower than the corresponding increase in O2 uptake. However, the differences were partly caused by insufficient mixing of media in the oxidation studies. D-Glucose (20 mM) released more than twice the amount of insulin than 5 mM alpha-ketoisocaproic acid, although O2 uptake in the islets did not differ. The results are consistent with the view that an increase in the production of metabolic energy is necessary for recognizing insulin-releasing fuels by B-cells.