title: Chromogranin A synthesis and secretion in chromaffin cells.
abstract: A sensitive and selective radioimmunoassay for chromogranin A (Chrg A) has been developed to quantitate content, release, and biosynthesis of this secretory protein in neuroendocrine tissues. An antiserum raised against Chrg A from bovine adrenal medulla was found to detect predominantly only the Mr 70-75 kilodalton Chrg A in its native form, allowing the use of this antiserum as a quantitatively specific probe for Chrg A in cell-free extracts of the adrenal medulla and chromaffin cells. Chrg A comprises about 10% of the total protein of the chromaffin cell. It is released in parallel with Met-enkephalin and catecholamines from the bovine chromaffin cell in primary culture in response to nicotine and nicotinic cholinergic agonists. From 14 to 22% of total Chrg A is released from the cell during a 15-min exposure to a maximally stimulatory dose of nicotine (10-100 microM). Chrg A release on nicotinic stimulation is blocked by D-600 and hexamethonium to the same extent as Met-enkephalin and catecholamine release. The parallel time course and percent release of Chrg A and Met-enkephalin indicate that these secretory polypeptides are contained in, and released from, functionally identical cellular compartments. Chrg A and Met-enkephalin pentapeptide sequences are present in the chromaffin cell at a ratio of about 2:1, although Chrg A is far more abundant on a mass basis. Chrg A and Met-enkephalin biosynthesis appear to be differentially regulated within the chromaffin cell, since chronic treatment of cells with nicotine and forskolin causes an elevation of Met-enkephalin pentapeptide without a concomitant elevation of intracellular levels of Chrg A.
mesh_terms: D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D002417:Cattle; D002837:Chromaffin Granules / Q000378:metabolism*; D002838:Chromaffin System / Q000378:metabolism*; D053379:Chromogranin A; D002864:Chromogranins / Q000096:biosynthesis* / Q000378:metabolism; D005576:Colforsin / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D004744:Enkephalin, Methionine / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000096:biosynthesis*; D009538:Nicotine / Q000494:pharmacology; D011863:Radioimmunoassay
chemical_list: D053379:Chromogranin A; D002864:Chromogranins; D009419:Nerve Tissue Proteins; D005576:Colforsin; D004744:Enkephalin, Methionine; D009538:Nicotine; D004837:Epinephrine