Glucose-induced cycles of insulin release can be resolved into distinct periods of secretory activity

The periodic behaviour of glucose-stimulated insulin release was studied using islets isolated from ob/ob-mice and rats. A single islet was perifused at a rate of 150 microliters/min and insulin measured in samples of the medium taken at intervals as short as 3 s. Exposure to 11 mM glucose resulted in intermittent insulin release, implying that previously observed 2-3 min cycles of secretion could be resolved into regularly occurring fast (< 25 s) transients. A further raise of glucose to 20 mM was associated with increase of the amplitudes of the transients leaving their frequencies unaffected. The discovery of the insulin transients raises the question whether there is a quantal release of the hormone in response to glucose-induced rapid oscillations of cytoplasmic Ca2+ in the pancreatic beta-cells.