title: R-type Ca(2+)-channel activity is associated with chromogranin A secretion in human neuroendocrine tumor BON cells.
abstract: This electrophysiological study was undertaken to investigate the role of voltage-operated Ca(2+) channels (VOCCs) in cultivated human neuroendocrine tumor (NET) cells. Patch-clamp techniques, measurements of intracellular Ca(2+) ([Ca(2+)](i)), and secretion analysis were performed using cultured human NET BON cells. Ba(2+) inward currents through R-type channels (Ca(V)2.3) were measured and identified by SNX-482 (10 n M), a novel voltage-sensitive R-type Ca(2+) channel antagonist. In the presence of nifedipine (5 micro M), omega-Conotoxin GVIA (100 n M) and omega-Agatoxin IVA (20 n M), R-type channel currents were also detectable. Release of Ca(2+) from intracellular Ca(2+) stores by intracellular application of inositol-1,4,5-trisphosphate (InsP(3); 10 micro M) via the patch pipette during whole-cell configuration as well as induction of capacitative Ca(2+) entry (CCE), a passive maneuver to release Ca(2+) from intracellular Ca(2+) stores, led to an increase in [Ca(2+)](i). This effect could be reduced by SNX-482 (20 n M). In addition, SNX-482 (25 n M) also decreased chromogranin A (CgA) secretion, whereas omega-Conotoxin GVIA (500 n M) and nifedipine (5 micro M) failed to reduce CgA secretion. We conclude that these data reveal neuronal R-type channel activity (Ca(V)2.3), for the first time associated with CgA secretion in BON cells. Influx of Ca(2+) by activation of R-type channels may lead to an increase of intracellular Ca(2+), which stimulates CgA secretion. Thus, R-type channels could play an important role in certain clinical characteristics of NETs, such as the hypersecretion syndrome.
mesh_terms: D001464:Barium / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020908:Calcium Channels, R-Type / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D053379:Chromogranin A; D002864:Chromogranins / Q000378:metabolism*; D006801:Humans; D007424:Intracellular Fluid / Q000378:metabolism; D017136:Ion Transport; D009363:Neoplasm Proteins / Q000378:metabolism; D018358:Neuroendocrine Tumors / Q000378:metabolism / Q000473:pathology*; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D018408:Patch-Clamp Techniques; D013111:Spider Venoms / Q000494:pharmacology; D014407:Tumor Cells, Cultured / Q000378:metabolism
chemical_list: C506150:CHGA protein, human; D002121:Calcium Channel Blockers; D020908:Calcium Channels, R-Type; D053379:Chromogranin A; D002864:Chromogranins; D009363:Neoplasm Proteins; C115521:SNX 482; D013111:Spider Venoms; D001464:Barium; D002118:Calcium