Synchronization of Islet Calcium Oscillations by Cholinergic Agonists
Abstract Number: 0010-OR
Authors: MIN ZHANG, BERNARD FENDLER, BRADLEY PEERCY, RICHARD BERTRAM, ARTHUR SHERMAN, LESLIE S. SATIN, Richmond, VA, Tallahassee, FL, Bethesda, MD
Results: While individual pancreatic islets exhibit oscillations in free calcium and insulin secretion in response to glucose in vitro, how these oscillations are coordinated between islets in vivo is poorly understood. This is a significant gap in our knowledge as islet-islet oscillations must be synchronized for the pancreas to produce pulses of insulin. To ascertain how synchronization might be accomplished, we simultaneously monitored free Ca levels in 4-6 islets using the Ca sensing dye fura-2. Mouse islets were isolated using collagenase digestion and maintained in culture overnight. When placed in a chamber held at 37o C and perifused with saline containing 11.1 mM glucose, islets exhibited regular Ca oscillations with a period of 3-6 minutes. Under these conditions, the Ca oscillations of neighboring islets were asynchronous even though the periods of the oscillations were similar. However, a 15 sec. application of the cholinergic agonist carbachol (25 µM) caused profound islet to islet synchronization in >50 experiments. In contrast, application of the adrenergic agonists clonidine or norepinephrine or the depolarizing agents KCl or tolbutamide failed to synchronize the islets. The action of carbachol was glucose-dependent, as carbachol applied in saline containing 5.5 or 7.5 mM glucose was much less effective in synchronizing neighboring islets. Cholinergic agonists increase both Ca influx and ER Ca release in islet beta cells. Synchronization persisted in islets treated with 1 µM thapsigargin to deplete their ER Ca stores suggesting that Ca influx is sufficient for islet to islet synchronization. Parallel computer simulations of model islets suggest a dynamic mechanism for the synchronization that we observe. These results suggest that acetylcholine release from intra-pancreatic neurons may help mediate islet to islet synchronization within the pancreas and the coordination of islet secretory oscillations. Supported by NIH DK RO146409 and NSF DMS 0613179.