Monoclonal anti-parathyroid antibodies interfering with a Ca2+-sensor of human parathyroid cells

Previous findings indicate that binding of Ca2+ to an external receptor is part of the mechanism by which extracellular Ca2+ regulates cytoplasmic Ca2+ and hormone release of parathyroid cells. We now present evidence that two newly generated monoclonal anti-parathyroid antibodies react with structures involved in this sensing and/or gating of Ca2+. Microfluorimetric studies of fura 2-loaded human parathyroid cells thus revealed that the antibodies competed with Ca2+ and antagonized the rise in cytoplasmic Ca2+ normally obtained when parathyroid cells are exposed to increasing concentrations of extracellular Ca2+.