The long term goals of this research project are to describe the biochemical events involved in glucose-induced insulin secretion by the pancreatic Beta-cell. This overall approach involves assessing the insulin secretory response in vitro in both intact and digitonin permeabilized islets and applying biochemical approaches with purified subcellular fractions to describe cellular mechanisms mediated at the plasma membrane and the secretory effector system involving the Beta-cell cytoskeleton. In this project we will characterize the effects of the cytokine interleukin-1 on islet function and determine its cellular mechanism in markedly modulating glucose-induced insulin release. The role for interleukin-1 and other cytokines as possible causative factors in the pathogenesis of insulin-dependent diabetes mellitus will be evaluated. The cellular mechanism in signal transduction whereby D-glucose is recognized by the Beta-cell and results in phospholipase C hydrolysis of plasma membrane polyphosphoinositides will be determined. The potential for insulin to modulate its release from the Beta-cell by a feed-back mechanism will be assessed by determining the existence of a plasma membrane functional insulin receptor based on 125I-insulin crosslinking to the Alpha-subunit and tyrosine kinase activity associated with the Beta-subunit of the insulin receptor. The role of the effector system in translocating insulin storage granules to the plasma membrane will be investigated by characterizing further both Ca2+- and calmodulin and phospholipid-dependent protein kinase activities in the process of exocytosis. The role of components of the Beta-cell cytoskeleton in exocytosis will also be evaluated by employing a recently developed biophysical technique which quantitates the mechanical resistance of the plasma membrane during the insulin secretory process.
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