CA2+ CALMODULIN AND CYCLIC 3,5'-ADENOSINE-MONOPHOSPHATE CONTROL MOVEMENT OF SECRETORY GRANULES THROUGH PROTEIN PHOSPHORYLATION/DEPHOSPHORYLATION IN THE PANCREATIC BETA-CELL/

We observed the movement of insulin granules in living transformed ham ster pancreatic beta-cells (HIT T15) with a light microscope, where se cretory granules are moving in the cytoplasmic space. Velocity of the typical granule movement was approximately 1.5 mu m/sec. A stimulatory concentration of glucose activated the movement of the secretory gran ules. Forskolin, an activator of adenylate cyclase, increased the move ment, resulting in changes in intracellular localization of the granul es. Acetylcholine also activated the granule movement, whereas high K and tolbutamide, which cause Ca2+ influx through the voltage-dependen t Ca2+ channel, had only little effect. The movement was abolished by BAPTA, the intracellular Ca2+ chelator. Activation of protein kinase C by 12-O-tetradecanoyl-phorbol Id-acetate failed to affect this moveme nt. The motile events were inhibited by the calmodulin antagonist, W-7 , and dramatically increased by okadaic acid, an inhibitor of protein phosphatases 1 and 2A. These results suggest protein phosphorylation b y Ca2+/calmodulin- and cAMP-dependent protein kinases play a positive role in the control of the insulin granule movements, which results in potentiation of insulin release from the pancreatic beta-cell.