An intriguing question in the physiology of the endocrine pancreas is how a rise in ambient glucose or amino acid concentration, a seemingly simple and ubiquitous stimulus which all cells are exposed to, results in the controlled pulsatile secretion of insulin by the B cell and inhibition of glucagon secretion by the A cell. The goal of this work is to study the role of single ion channels in the coupling of metabolite stimuli to insulin and glucagon secretion. Principally, we wish to examine whether stimulation by a metabolite results in B cell depolarization (and hence voltage-dependent Ca2+ influx) by inducing closure of an ATP sensitive K+ channel. To do this we shall examine the salient characteristics of this channel including ion selectivity, gating, single channel kinetics and pharmacology of this channel. These experiments will involve standard cell attached and excised patch recording, whole cell recording, cell attached patch recording with partially permeabilized cells and a novel """"""""slow"""""""" whole cell technique. Second, we wish to examine whether intracellular release of Ca2+ in B cell, which may also be stimulated by metabolism, occurs through Ca2+ channels in endoplasmic reticulum (ER), by measuring Ca2+ channel activity of insulinoma ER fused into planar bilayer membranes. We also wish to determine whether this source of intracellular calcium contributes to a pool of Ca2+ which participates in triggering insulin exocytosis, using Ca2+-activated K+ channels in cell attached patches of partially permeabilized cells as an assay for local Ca2+ concentration. Third, we wish to begin exploring single channels underlying electrical activity in immunocytochemically identified A cells. Results of these experiments should contribute to our knowledge of stimulus-secretion coupling in the endocrine pancreas and pave the way for future investigations of membrane defects in diabetes mellitus.
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