Imaging of Ca2+-induced cytoplasmic Ca2+ responses in normal and pathological parathyroid cells

Ca²⁺-induced changes in the cytoplasmic Ca²⁺ concentration (Ca²⁺]_i) were studied in bovine and normal and pathological human parathyroid cells using digital image analysis of fura-2-loaded cells. When raising external Ca²⁺ from 0.5 to 3.0 mmol L^?1, about 95% of all cells reacted rapidly and simultaneously with sustained elevation of Ca²⁺]_i. In approximately two out of three bovine parathyroid cells, normal human cells and cells from most patients with hyperparathyroidism (HPT) the sustained phase was preceded by an overshooting Ca²⁺]_i transient. The proportion of cells with such a transient was decreased in cells from severe cases of uraemic parathyroid hyperplasia only. However, pathological human cells from adenomas and normal-sized glands associated with adenomas, as well as cells from primary and uraemic hyperplasias, had lower peak and sustained levels than normal human and bovine cells. The results indicate that both normal and pathological parathyroid cells exhibit heterogeneity in their Ca²⁺]_i responses to elevation of external Ca²⁺. The Ca²⁺-induced Ca²⁺]_i transients and the sustained elevations are attenuated in pathological human parathyroid cells. However, the presence of the overshooting transient represents physiological variability rather than being a consequence of the pathophysiology associated with HPT.