Chromogranin-A secretion from individual parathyroid cells: effects of 1,25-(OH)2 vitamin D3 and calcium.

Chromogranin-A (CgA) is a 50-kDa protein located in and secreted by most endocrine and neuroendocrine cells along with native hormone. In the parathyroid gland, CgA is cosecreted with parathyroid hormone (PTH). Although these peptides are secreted together, recent evidence has suggested that they are processed differently in response to stimuli, such as 1,25-(OH)2 vitamin D3 and calcium. We have validated a reverse hemolytic plaque assay for studying CgA release from parathyroid cells. This assay allows for the detection of quantitative changes in hormone secretion from individual parathyroid cells. Bovine parathyroid cells were mixed with protein-A-linked ovine erythrocytes (oRBC) and plated in a monolayer in the presence of CgA antiserum. After incubation, complement was added to the cells to induce cell lysis. Lysis of oRBC around a parathyroid cell indicated the release of CgA from a cell. Results showed that plaque formation was dependent on assay reagents and that serial dilution of the antibody reduced plaque formation. CgA secretion was inhibited by increasing concentrations of calcium and stimulated by increasing concentrations of 1,25-(OH)2vitamin D3.