Individual parathyroid cells exhibit cyclic secretion of parathyroid hormone and chromogranin-A (as measured by a novel sequential hemolytic plaque assay).

PTH and chromogranin-A (CgA) are the two major proteins secreted from the parathyroid gland. We investigated the secretory patterns of CgA and PTH using a sequential reverse hemolytic plaque assay (RHPA). The RHPA allows detection of hormone secretion from individual cells after a secretory stimulus. For the sequential RHPA, bovine parathyroid cells were mixed with protein-A-conjugated ovine erythrocytes (oRBC). Antiserum, either anti-PTH or anti-CgA, was added under optimal secretory conditions. The addition of complement caused lysis of oRBC surrounding hormone-secreting cells. In this stage (stage 1), individual cells were identified and indexed as secreting or nonsecreting cells. For stage 2, a new lawn of oRBC was established, and a second RHPA was performed on the same population of cells, allowing for the detection of secretory patterns. In the single stage RHPA, about three fourths of the cells formed CgA plaques compared to only about half that formed PTH plaques, suggesting that CgA and PTH are not always cosecreted. In the sequential RHPA, of the cells that did not secrete CgA or PTH in stage 1, up to half secreted in stage 2. Of those cells that secreted in stage 1, up to one fourth did not secrete in stage 2. These results indicate that the parathyroid cells "cycled" between secretory and nonsecretory phases. Our experimental design precluded our obtaining unequivocal data on whether CgA is an autocrine/paracrine regulator of PTH secretion.