Hormone secretion by normal human parathyroid cells in vitro: characterization by the reverse hemolytic plaque assay

We have recently validated a reverse hemolytic plaque assay (RHPA) for the quantitative measurement of parathyroid hormone release from single isolated parathyroid cells. The information regarding secretory behavior of normal and abnormal parathyroid tissue has been based previously on fluorescent spectroscopy or quantification of immunoreactive parathyroid hormone by radioimmunoassay. Thus, individual differences in secretion and assessment of viability are not clearly measured in these types of experiments. The RHPA has the advantage of allowing measurements of secretory activity in individual viable parathyroid cells. In this report, we have modified the RHPA to measure the release of parathyroid hormone from human cells. This is the first instance of measurement of hormone secretion from human cells, and we present data indicating the specificity of the assay for human parathyroid hormone. The response of normal human parathyroid cells to alterations in extracellular calcium was assessed by two parameters: the ability of an individual cell to secrete parathyroid hormone in response to a stimulus and the recruitment of normal human cells to release parathyroid hormone. This assay will allow elucidation of secretory dynamics in normal and abnormal glands, which may help us to understand the mechanisms involved in parathyroid dysfunction.