Relation between redox state and secretory response to brain-gut peptides

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Microspectrofluorimetry with fura-2 was utilized to monitor cytosolic concentration of calcium ion, [Ca^<2+>]_i, in single cells of the isolated pancreatic acini during continuous stimulation with C-terminal octapeptide of cholecystokinin (CCK-8). Prior to the microspectrofluorimtry, the same cells were examined under the Nomarski differential interference contrast optical system. Regional morphological differences could be resolved, insofar as, the apical half of an acinar cell contained a large number of zymogen granules (ZG region), whereas the basal half appeared clear with few granulation (region of endoplasmic reticulum; ER region). When acinar cells were continuously stimulated with 30pM CCK-8, which is known to cause sustained increase in amylase release from pancreatic acini, oscillation of [Ca^<2+>]_i was usually observed in the ER region, whereas a single transient increase in [Ca^<2+>]_i was usually detected in the ZG region. The oscillatory change in [Ca^<2+>]_i consisted of three components: 1) an initial transient increase flowed by 2) a gradual decline, upon which 30 pM CCK-8 during perfusion with a Ca^<2+>-free solution, the initial transient increase in [Ca^<2+>]_i remained but the secondary oscillations were abolished. A single transient increase in [Ca^<2+>]_i without any subsequent oscillation was observed when the acinar cells were continuously stimulated with 100pM CCK-8. Secretory responses of acinar cells to 30pM CCK-8 were not interfered with fura-2 AM (10mum), but these to 100 pM CCK-8 were significantly inhibited with fura-2 AM. These results show that the CCK-8-induced oscillatory changes in [Ca^<2+>]_i may play a significant role in the stimulus-secretion coupling in the pancreatic acinar cell.