Dual effects of a new hypocalcemic agent, WR-2721, on cytoplasmic Ca2+ and parathyroid hormone release of dispersed parathyroid cells from patients with hyperparathyroidism.

The effects of the new hypocalcemic agent, WR-2721, on calcium-regulated parathyroid hormone (PTH) release, cytoplasmic Ca2+ (Ca2+i) and membrane potential were measured in dispersed parathyroid cells from patients with hyperparathyrodisim (HPT). The drug had no effects in the absence of extracellular Ca2+ but acted synergistically with Ca2+ in the 0.5-1.5 mM range by depolarizing the cells, increasing Ca2+i and inhibiting PTH release. Although the depolarizing effect of 3.0 mM Ca2+ was unaffected by WR-2721 the drug antagonized the effect of Ca2+ by decreasing Ca2+i and stimulating PTH release. Whereas the inhibitory actions of WR-2721 on PTH release may result from the activation of the mechanism for Ca2+ gating in the parathyroid cell plasma membrane, the stimulatory effect probably reflects increased intracellular Ca2+ sequestration. The drug is considered potentially important for the treatment of HPT.